In Press
In Press articles are edited and published online ahead of issue. When the final article is assigned to volumes/issues, the Article in Press version will be removed and the final version will appear in the associated published volumes/issues.
+ show detail
Surface plasmon assisted high-performance photodetectors based on hybrid TiO2@GaOxNy-Ag heterostructure
Jiajia Tao, Guang Zeng, Xiaoxi Li, Yang Gu, Wenjun Liu, David Wei Zhang, Hongliang Lu
, Available online  

In this work, we reported a high-performance-based ultraviolet-visible (UV-VIS) photodetector based on a TiO2@GaOxNy-Ag heterostructure. Ag particles were introduced into TiO2@GaOxNy to enhance the visible light detection performance of the heterojunction device. At 380 nm, the responsivity and detectivity of TiO2@GaOxNy-Ag were 0.94 A/W and 4.79 × 109 Jones, respectively, and they increased to 2.86 A/W and 7.96 × 1010 Jones at 580 nm. The rise and fall times of the response were 0.19/0.23 and 0.50/0.57 s, respectively. Uniquely, at 580 nm, the responsivity of fabricated devices is one to four orders of magnitude higher than that of the photodetectors based on TiO2, Ga2O3, and other heterojunctions. The excellent optoelectronic characteristics of the TiO2@GaOxNy-Ag heterojunction device could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag, which not only effectively promotes the separation of photogenerated carriers but also reduces the recombination rate. It is further illuminated by finite difference time domain method (FDTD) simulation and photoelectric measurements. The TiO2@GaOxNy-Ag arrays with high-efficiency detection are suitable candidates for applications in energy-saving communication, imaging, and sensing networks.

In this work, we reported a high-performance-based ultraviolet-visible (UV-VIS) photodetector based on a TiO2@GaOxNy-Ag heterostructure. Ag particles were introduced into TiO2@GaOxNy to enhance the visible light detection performance of the heterojunction device. At 380 nm, the responsivity and detectivity of TiO2@GaOxNy-Ag were 0.94 A/W and 4.79 × 109 Jones, respectively, and they increased to 2.86 A/W and 7.96 × 1010 Jones at 580 nm. The rise and fall times of the response were 0.19/0.23 and 0.50/0.57 s, respectively. Uniquely, at 580 nm, the responsivity of fabricated devices is one to four orders of magnitude higher than that of the photodetectors based on TiO2, Ga2O3, and other heterojunctions. The excellent optoelectronic characteristics of the TiO2@GaOxNy-Ag heterojunction device could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag, which not only effectively promotes the separation of photogenerated carriers but also reduces the recombination rate. It is further illuminated by finite difference time domain method (FDTD) simulation and photoelectric measurements. The TiO2@GaOxNy-Ag arrays with high-efficiency detection are suitable candidates for applications in energy-saving communication, imaging, and sensing networks.
Homoepitaxial growth of (100) Si-doped β-Ga2O3 films via MOCVD
Wenbo Tang, Xueli Han, Xiaodong Zhang, Botong Li, Yongjian Ma, Li Zhang, Tiwei Chen, Xin Zhou, Chunxu Bian, Yu Hu, Duanyang Chen, Hongji Qi, Zhongming Zeng, Baoshun Zhang
, Available online  
doi: 10.1088/1674-4926/44/6/062801

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.
Preparation of Sn-doped Ga2O3 thin films and their solar-blind photoelectric detection performance
Lijun Li, Chengkun Li, Shaoqing Wang, Qin Lu, Yifan Jia, Haifeng Chen
, Available online  
doi: 10.1088/1674-4926/44/6/062805

Sn doping is an effective way to improve the response rate of Ga2O3 film based solar-blind detectors. In this paper, Sn-doped Ga2O3 films were prepared on a sapphire substrate by radio frequency magnetron sputtering. The films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet visible spectroscopy, and the effect of annealing atmosphere on the properties of films was studied. The Ga2O3 films changed from amorphous to β-Ga2O3 after annealing at 900 °C. The films were composed of micro crystalline particles with a diameter of about 5–20 nm. The β-Ga2O3 had high transmittance for wavelengths above 300 nm, and obvious absorption for solar-blind signals at 200–280 nm. The metal semiconductor metal type solar-blind detectors were prepared. The detector based on Sn-doped β-Ga2O3 thin film annealed in N2 has the best response performance to 254 nm light. The photo-current is 10 μA at 20 V, the dark-current is 5.76 pA, the photo dark current ratio is 1.7 × 106, the response rate is 12.47 A/W, the external quantum efficiency is 6.09 × 103%, the specific detection rate is 2.61 × 1012 Jones, the response time and recovery time are 378 and 90 ms, respectively.

Sn doping is an effective way to improve the response rate of Ga2O3 film based solar-blind detectors. In this paper, Sn-doped Ga2O3 films were prepared on a sapphire substrate by radio frequency magnetron sputtering. The films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet visible spectroscopy, and the effect of annealing atmosphere on the properties of films was studied. The Ga2O3 films changed from amorphous to β-Ga2O3 after annealing at 900 °C. The films were composed of micro crystalline particles with a diameter of about 5–20 nm. The β-Ga2O3 had high transmittance for wavelengths above 300 nm, and obvious absorption for solar-blind signals at 200–280 nm. The metal semiconductor metal type solar-blind detectors were prepared. The detector based on Sn-doped β-Ga2O3 thin film annealed in N2 has the best response performance to 254 nm light. The photo-current is 10 μA at 20 V, the dark-current is 5.76 pA, the photo dark current ratio is 1.7 × 106, the response rate is 12.47 A/W, the external quantum efficiency is 6.09 × 103%, the specific detection rate is 2.61 × 1012 Jones, the response time and recovery time are 378 and 90 ms, respectively.
Heterogeneous integration technology for the thermal management of Ga2O3 power devices
Genquan Han, Tiangui You, Yibo Wang, Zheng-Dong Luo, Xin Ou, Yue Hao
, Available online  
doi: 10.1088/1674-4926/44/6/060301

Rapid epitaxy of 2-inch and high-quality α-Ga2O3 films by mist-CVD method
Xiaojie Wang, Wenxiang Mu, Jiahui Xie, Jinteng Zhang, Yang Li, Zhitai Jia, Xutang Tao
, Available online  
doi: 10.1088/1674-4926/44/6/062803

High thickness uniformity and large-scale films of α-Ga2O3 are crucial factors for the development of power devices. In this work, a high-quality 2-inch α-Ga2O3 epitaxial film on c-plane sapphire substrates was prepared by the mist-CVD method. The growth rate and phase control mechanisms were systematically investigated. The growth rate of the α-Ga2O3 films was limited by the evaporation of the microdroplets containing gallium acetylacetonate. By adjusting the substrate position (z) from 80 to 50 mm, the growth rate was increased from 307 nm/h to 1.45 μm/h when the growth temperature was fixed at 520 °C. When the growth temperature exceeded 560 °C, ε-Ga2O3 was observed to form at the edges of 2-inch sapphire substrate. Phase control was achieved by adjusting the growth temperature. When the growth temperature was 540 °C and the substrate position was 50 mm, the full-width at half maximum (FWHM) of the rocking curves for the (0006) and (10-14) planes were 0.023° and 1.17°. The screw and edge dislocations were 2.3 × 106 and 3.9 × 1010 cm-2, respectively. Furthermore, the bandgaps and optical transmittance of α-Ga2O3 films grown under different conditions were characterized utilizing UV-visible and near-IR scanning spectra.

High thickness uniformity and large-scale films of α-Ga2O3 are crucial factors for the development of power devices. In this work, a high-quality 2-inch α-Ga2O3 epitaxial film on c-plane sapphire substrates was prepared by the mist-CVD method. The growth rate and phase control mechanisms were systematically investigated. The growth rate of the α-Ga2O3 films was limited by the evaporation of the microdroplets containing gallium acetylacetonate. By adjusting the substrate position (z) from 80 to 50 mm, the growth rate was increased from 307 nm/h to 1.45 μm/h when the growth temperature was fixed at 520 °C. When the growth temperature exceeded 560 °C, ε-Ga2O3 was observed to form at the edges of 2-inch sapphire substrate. Phase control was achieved by adjusting the growth temperature. When the growth temperature was 540 °C and the substrate position was 50 mm, the full-width at half maximum (FWHM) of the rocking curves for the (0006) and (10-14) planes were 0.023° and 1.17°. The screw and edge dislocations were 2.3 × 106 and 3.9 × 1010 cm-2, respectively. Furthermore, the bandgaps and optical transmittance of α-Ga2O3 films grown under different conditions were characterized utilizing UV-visible and near-IR scanning spectra.
Investigation of β-Ga2O3 thick films grown on c-plane sapphire via carbothermal reduction
Liyuan Cheng, Hezhi Zhang, Wenhui Zhang, Hongwei Liang
, Available online  
doi: 10.1088/1674-4926/44/6/062804

We investigated the influence of the growth temperature, O2 flow, molar ratio between Ga2O3 powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire (0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga2O3 illustrate that β-Ga2O3 growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga2O3 films was produced when the O2 flow was 20 sccm. To guarantee that β-Ga2O3 films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga2O3 powder should be set at 10 : 1.

We investigated the influence of the growth temperature, O2 flow, molar ratio between Ga2O3 powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire (0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga2O3 illustrate that β-Ga2O3 growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga2O3 films was produced when the O2 flow was 20 sccm. To guarantee that β-Ga2O3 films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga2O3 powder should be set at 10 : 1.
Recent advances in NiO/Ga2O3 heterojunctions for power electronics
Xing Lu, Yuxin Deng, Yanli Pei, Zimin Chen, Gang Wang
, Available online  
doi: 10.1088/1674-4926/44/6/061802

Beta gallium oxide (β-Ga2O3) has attracted significant attention for applications in power electronics due to its ultra-wide bandgap of ~ 4.8 eV and the large critical electric field of 8 MV/cm. These properties yield a high Baliga’s figures of merit (BFOM) of more than 3000. Though β-Ga2O3 possesses superior material properties, the lack of p-type doping is the main obstacle that hinders the development of β-Ga2O3-based power devices for commercial use. Constructing heterojunctions by employing other p-type materials has been proven to be a feasible solution to this issue. Nickel oxide (NiO) is the most promising candidate due to its wide band gap of 3.6–4.0 eV. So far, remarkable progress has been made in NiO/β-Ga2O3 heterojunction power devices. This review aims to summarize recent advances in the construction, characterization, and device performance of the NiO/β-Ga2O3 heterojunction power devices. The crystallinity, band structure, and carrier transport property of the sputtered NiO/β-Ga2O3 heterojunctions are discussed. Various device architectures, including the NiO/β-Ga2O3 heterojunction pn diodes (HJDs), junction barrier Schottky (JBS) diodes, and junction field effect transistors (JFET), as well as the edge terminations and super-junctions based on the NiO/β-Ga2O3 heterojunction, are described.

Beta gallium oxide (β-Ga2O3) has attracted significant attention for applications in power electronics due to its ultra-wide bandgap of ~ 4.8 eV and the large critical electric field of 8 MV/cm. These properties yield a high Baliga’s figures of merit (BFOM) of more than 3000. Though β-Ga2O3 possesses superior material properties, the lack of p-type doping is the main obstacle that hinders the development of β-Ga2O3-based power devices for commercial use. Constructing heterojunctions by employing other p-type materials has been proven to be a feasible solution to this issue. Nickel oxide (NiO) is the most promising candidate due to its wide band gap of 3.6–4.0 eV. So far, remarkable progress has been made in NiO/β-Ga2O3 heterojunction power devices. This review aims to summarize recent advances in the construction, characterization, and device performance of the NiO/β-Ga2O3 heterojunction power devices. The crystallinity, band structure, and carrier transport property of the sputtered NiO/β-Ga2O3 heterojunctions are discussed. Various device architectures, including the NiO/β-Ga2O3 heterojunction pn diodes (HJDs), junction barrier Schottky (JBS) diodes, and junction field effect transistors (JFET), as well as the edge terminations and super-junctions based on the NiO/β-Ga2O3 heterojunction, are described.
Preface to Special Issue on Towards High Performance Ga2O3 Electronics: Epitaxial Growth and Power Devices (Ⅰ)
Genquan Han, Shibing Long, Yuhao Zhang, Yibo Wang, Zhongming Wei
, Available online  
doi: 10.1088/1674-4926/44/6/060101

Solution-processed CuIn(S,Se)2 solar cells on transparent electrode offering 9.4% efficiency
Xinge Liu, Chengfeng Ma, Hao Xin, Liming Ding
, Available online  
doi: 10.1088/1674-4926/44/8/080501

A comprehensive review of recent progress on enhancement-mode β-Ga2O3 FETs: Growth, devices and properties
Botong Li, Xiaodong Zhang, Li Zhang, Yongjian Ma, Wenbo Tang, Tiwei Chen, Yu Hu, Xin Zhou, Chunxu Bian, Chunhong Zeng, Tao Ju, Zhongming Zeng, Baoshun Zhang
, Available online  
doi: 10.1088/1674-4926/44/6/061801

Power electronic devices are of great importance in modern society. After decades of development, Si power devices have approached their material limits with only incremental improvements and large conversion losses. As the demand for electronic components with high efficiency dramatically increasing, new materials are needed for power device fabrication. Beta-phase gallium oxide, an ultra-wide bandgap semiconductor, has been considered as a promising candidate, and various β-Ga2O3 power devices with high breakdown voltages have been demonstrated. However, the realization of enhancement-mode (E-mode) β-Ga2O3 field-effect transistors (FETs) is still challenging, which is a critical problem for a myriad of power electronic applications. Recently, researchers have made some progress on E-mode β-Ga2O3 FETs via various methods, and several novel structures have been fabricated. This article gives a review of the material growth, devices and properties of these E-mode β-Ga2O3 FETs. The key challenges and future directions in E-mode β-Ga2O3 FETs are also discussed.

Power electronic devices are of great importance in modern society. After decades of development, Si power devices have approached their material limits with only incremental improvements and large conversion losses. As the demand for electronic components with high efficiency dramatically increasing, new materials are needed for power device fabrication. Beta-phase gallium oxide, an ultra-wide bandgap semiconductor, has been considered as a promising candidate, and various β-Ga2O3 power devices with high breakdown voltages have been demonstrated. However, the realization of enhancement-mode (E-mode) β-Ga2O3 field-effect transistors (FETs) is still challenging, which is a critical problem for a myriad of power electronic applications. Recently, researchers have made some progress on E-mode β-Ga2O3 FETs via various methods, and several novel structures have been fabricated. This article gives a review of the material growth, devices and properties of these E-mode β-Ga2O3 FETs. The key challenges and future directions in E-mode β-Ga2O3 FETs are also discussed.
Exploring heteroepitaxial growth and electrical properties of α-Ga2O3 films on differently oriented sapphire substrates
Wei Wang, Shudong Hu, Zilong Wang, Kaisen Liu, Jinfu Zhang, Simiao Wu, Yuxia Yang, Ning Xia, Wenrui Zhang, Jichun Ye
, Available online  
doi: 10.1088/1674-4926/44/6/062802

This study explores the epitaxial relationship and electrical properties of α-Ga2O3 thin films deposited on a-plane, m-plane, and r-plane sapphire substrates. We characterize the thin films by X-ray diffraction and Raman spectroscopy, and elucidate thin film epitaxial relationships with the underlying sapphire substrates. The oxygen vacancy concentration of α-Ga2O3 thin films on m-plane and r-plane sapphire substrates are higher than α-Ga2O3 thin film on a-plane sapphire substrates. All three thin films have a high transmission of over 80% in the visible and near-ultraviolet regions, and their optical bandgaps stay around 5.02–5.16 eV. Hall measurements show that the α-Ga2O3 thin film grown on r-plane sapphire has the highest conductivity of 2.71 S/cm, which is at least 90 times higher than the film on a-plane sapphire. A similar orientation-dependence is seen in their activation energy as revealed by temperature-dependent conductivity measurements, with 0.266, 0.079, and 0.075 eV for the film on a-, m-, r-plane, respectively. The origin of the distinct transport behavior of films on differently oriented substrates is suggested to relate with the distinct evolution of oxygen vacancies at differently oriented substrates. This study provides insights for the substrate selection when growing α-Ga2O3 films with tunable transport properties.

This study explores the epitaxial relationship and electrical properties of α-Ga2O3 thin films deposited on a-plane, m-plane, and r-plane sapphire substrates. We characterize the thin films by X-ray diffraction and Raman spectroscopy, and elucidate thin film epitaxial relationships with the underlying sapphire substrates. The oxygen vacancy concentration of α-Ga2O3 thin films on m-plane and r-plane sapphire substrates are higher than α-Ga2O3 thin film on a-plane sapphire substrates. All three thin films have a high transmission of over 80% in the visible and near-ultraviolet regions, and their optical bandgaps stay around 5.02–5.16 eV. Hall measurements show that the α-Ga2O3 thin film grown on r-plane sapphire has the highest conductivity of 2.71 S/cm, which is at least 90 times higher than the film on a-plane sapphire. A similar orientation-dependence is seen in their activation energy as revealed by temperature-dependent conductivity measurements, with 0.266, 0.079, and 0.075 eV for the film on a-, m-, r-plane, respectively. The origin of the distinct transport behavior of films on differently oriented substrates is suggested to relate with the distinct evolution of oxygen vacancies at differently oriented substrates. This study provides insights for the substrate selection when growing α-Ga2O3 films with tunable transport properties.
Study of quantum well mixing induced by impurity-free vacancy in the primary epitaxial wafers of a 915 nm semiconductor laser
Tianjiang He, Suping Liu, Wei Li, Li Zhong, Xiaoyu Ma, Cong Xiong, Nan Lin, Zhennuo Wang
, Available online  

Output power and reliability are the most important characteristic parameters of semiconductor lasers. However, catastrophic optical damage (COD), which usually occurs on the cavity surface, will seriously damage the further improvement of the output power and affect the reliability. To improve the anti-optical disaster ability of the cavity surface, a non-absorption window (NAW) is adopted for the 915 nm InGaAsP/GaAsP single-quantum well semiconductor laser using quantum well mixing (QWI) induced by impurity-free vacancy. Both the principle and the process of point defect diffusion are described in detail in this paper. We also studied the effects of annealing temperature, annealing time, and the thickness of SiO2 film on the quantum well mixing in a semiconductor laser with a primary epitaxial structure, which is distinct from the previous structures. We found that when compared with the complete epitaxial structure, the blue shift of the semiconductor laser with the primary epitaxial structure is larger under the same conditions. To obtain the appropriate blue shift window, the primary epitaxial structure can use a lower annealing temperature and shorter annealing time. In addition, the process is less expensive. We also provide references for upcoming device fabrication.

Output power and reliability are the most important characteristic parameters of semiconductor lasers. However, catastrophic optical damage (COD), which usually occurs on the cavity surface, will seriously damage the further improvement of the output power and affect the reliability. To improve the anti-optical disaster ability of the cavity surface, a non-absorption window (NAW) is adopted for the 915 nm InGaAsP/GaAsP single-quantum well semiconductor laser using quantum well mixing (QWI) induced by impurity-free vacancy. Both the principle and the process of point defect diffusion are described in detail in this paper. We also studied the effects of annealing temperature, annealing time, and the thickness of SiO2 film on the quantum well mixing in a semiconductor laser with a primary epitaxial structure, which is distinct from the previous structures. We found that when compared with the complete epitaxial structure, the blue shift of the semiconductor laser with the primary epitaxial structure is larger under the same conditions. To obtain the appropriate blue shift window, the primary epitaxial structure can use a lower annealing temperature and shorter annealing time. In addition, the process is less expensive. We also provide references for upcoming device fabrication.
Preparation and photodetection performance of high crystalline quality and large size β-Ga2O3 microwires
Yuefei Wang, Yurui Han, Chong Gao, Bingsheng Li, Jiangang Ma, Haiyang Xu, Aidong Shen, Yichun Liu
, Available online  
doi: 10.1088/1674-4926/44/6/062806

Ultrawide band gap semiconductors are promising solar-blind ultraviolet (UV) photodetector materials due to their suitable bandgap, strong absorption and high sensitivity. Here, β-Ga2O3 microwires with high crystal quality and large size were grown by the chemical vapor deposition (CVD) method. The microwires reach up to 1 cm in length and were single crystalline with low defect density. Owing to its high crystal quality, a metal–semiconductor–metal photodetector fabricated from a Ga2O3 microwire showed a responsivity of 1.2 A/W at 240 nm with an ultrahigh UV/visible rejection ratio (Rpeak/R400 nm) of 5.8 × 105, indicating that the device has excellent spectral selectivity. In addition, no obvious persistent photoconductivity was observed in the test. The rise and decay time constants of the device were 0.13 and 0.14 s, respectively. This work not only provides a growth method for high-quality Ga2O3 microwires, but also demonstrates the excellent performance of Ga2O3 microwires in solar-blind ultraviolet detection.

Ultrawide band gap semiconductors are promising solar-blind ultraviolet (UV) photodetector materials due to their suitable bandgap, strong absorption and high sensitivity. Here, β-Ga2O3 microwires with high crystal quality and large size were grown by the chemical vapor deposition (CVD) method. The microwires reach up to 1 cm in length and were single crystalline with low defect density. Owing to its high crystal quality, a metal–semiconductor–metal photodetector fabricated from a Ga2O3 microwire showed a responsivity of 1.2 A/W at 240 nm with an ultrahigh UV/visible rejection ratio (Rpeak/R400 nm) of 5.8 × 105, indicating that the device has excellent spectral selectivity. In addition, no obvious persistent photoconductivity was observed in the test. The rise and decay time constants of the device were 0.13 and 0.14 s, respectively. This work not only provides a growth method for high-quality Ga2O3 microwires, but also demonstrates the excellent performance of Ga2O3 microwires in solar-blind ultraviolet detection.
Anisotropic optical and electric properties of β-gallium oxide
Yonghui Zhang, Fei Xing
, Available online  

The anisotropic properties and applications of β-gallium oxide (β-Ga2O3) are comprehensively reviewed. All the anisotropic properties are essentially resulted from the anisotropic crystal structure. The process flow of how to exfoliate nanoflakes from bulk material is introduced. Anisotropic optical properties, including optical bandgap, Raman and photoluminescence characters are comprehensively reviewed. Three measurement configurations of angle-resolved polarized Raman spectra (ARPRS) are reviewed, with Raman intensity formulas calculated with Raman tensor elements. The method to obtain the Raman tensor elements of phonon modes through experimental fitting is also introduced. In addition, the anisotropy in electron mobility and affinity are discussed. The applications, especially polarization photodetectors, based on β-Ga2O3 were summarized comprehensively. Three kinds of polarization detection mechanisms based on material dichroism, 1D morphology and metal-grids are discussed in-depth. This review paper provides a framework for anisotropic optical and electric properties of β-Ga2O3, as well as the applications based on these characters, and is expected to lead to a wider discussion on this topic.

The anisotropic properties and applications of β-gallium oxide (β-Ga2O3) are comprehensively reviewed. All the anisotropic properties are essentially resulted from the anisotropic crystal structure. The process flow of how to exfoliate nanoflakes from bulk material is introduced. Anisotropic optical properties, including optical bandgap, Raman and photoluminescence characters are comprehensively reviewed. Three measurement configurations of angle-resolved polarized Raman spectra (ARPRS) are reviewed, with Raman intensity formulas calculated with Raman tensor elements. The method to obtain the Raman tensor elements of phonon modes through experimental fitting is also introduced. In addition, the anisotropy in electron mobility and affinity are discussed. The applications, especially polarization photodetectors, based on β-Ga2O3 were summarized comprehensively. Three kinds of polarization detection mechanisms based on material dichroism, 1D morphology and metal-grids are discussed in-depth. This review paper provides a framework for anisotropic optical and electric properties of β-Ga2O3, as well as the applications based on these characters, and is expected to lead to a wider discussion on this topic.
Amorphous gallium oxide homojunction-based optoelectronic synapse for multi-functional signal processing
Rongliang Li, Yonghui Lin, Yang Li, Song Gao, Wenjing Yue, Hao Kan, Chunwei Zhang, Guozhen Shen
, Available online  

In the era of accelerated development in artificial intelligence as well as explosive growth of information and data throughput, underlying hardware devices that can integrate perception and memory while simultaneously offering the benefits of low power consumption and high transmission rates are particularly valuable. Neuromorphic devices inspired by the human brain are considered to be one of the most promising successors to the efficient in-sensory process. In this paper, a homojunction-based multi-functional optoelectronic synapse (MFOS) is proposed and testified. It enables a series of basic electrical synaptic plasticity, including paired-pulse facilitation/depression (PPF/PPD) and long-term promotion/depression (LTP/LTD). In addition, the synaptic behaviors induced by electrical signals could be instead achieved through optical signals, where its sensitivity to optical frequency allows the MFOS to simulate high-pass filtering applications in situ and the perception capability integrated into memory endows it with the information acquisition and processing functions as a visual system. Meanwhile, the MFOS exhibits its performances of associative learning and logic gates following the illumination with two different wavelengths. As a result, the proposed MFOS offers a solution for the realization of intelligent visual system and bionic electronic eye, and will provide more diverse application scenarios for future neuromorphic computing.

In the era of accelerated development in artificial intelligence as well as explosive growth of information and data throughput, underlying hardware devices that can integrate perception and memory while simultaneously offering the benefits of low power consumption and high transmission rates are particularly valuable. Neuromorphic devices inspired by the human brain are considered to be one of the most promising successors to the efficient in-sensory process. In this paper, a homojunction-based multi-functional optoelectronic synapse (MFOS) is proposed and testified. It enables a series of basic electrical synaptic plasticity, including paired-pulse facilitation/depression (PPF/PPD) and long-term promotion/depression (LTP/LTD). In addition, the synaptic behaviors induced by electrical signals could be instead achieved through optical signals, where its sensitivity to optical frequency allows the MFOS to simulate high-pass filtering applications in situ and the perception capability integrated into memory endows it with the information acquisition and processing functions as a visual system. Meanwhile, the MFOS exhibits its performances of associative learning and logic gates following the illumination with two different wavelengths. As a result, the proposed MFOS offers a solution for the realization of intelligent visual system and bionic electronic eye, and will provide more diverse application scenarios for future neuromorphic computing.
Terahertz phononic crystal in plasmonic nanocavity
Zhenyao Li, Haonan Chang, Jia-Min Lai, Feilong Song, Qifeng Yao, Hanqing Liu, Haiqiao Ni, Zhichuan Niu, Jun Zhang
, Available online  
doi: 10.1088/1674-4926/44/8/082901

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies. A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency (~THz). However, the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light. Here, we design a system that combines Ag nanocavity with GaAs/AlAs phononic superlattices, where phonons with the frequency of 4.2 THz can be confined in a pillar with ~4 nm diameter. The Q c/V reaches 0.22 nm-3, which is ~80 times that of the photonic crystal (PhC) nanobeam and ~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity, where Q­c is optical quality factor and V is mode volume. The optomechanical single-photon coupling strength can reach 12 MHz, which is an order of magnitude larger than that of the PhC nanobeam. In addition, the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg, which is much smaller than the PhC nanobeam. The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics, quantum information, and terahertz-light transducer.

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies. A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency (~THz). However, the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light. Here, we design a system that combines Ag nanocavity with GaAs/AlAs phononic superlattices, where phonons with the frequency of 4.2 THz can be confined in a pillar with ~4 nm diameter. The Q c/V reaches 0.22 nm-3, which is ~80 times that of the photonic crystal (PhC) nanobeam and ~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity, where Q­c is optical quality factor and V is mode volume. The optomechanical single-photon coupling strength can reach 12 MHz, which is an order of magnitude larger than that of the PhC nanobeam. In addition, the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg, which is much smaller than the PhC nanobeam. The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics, quantum information, and terahertz-light transducer.
Photodetector based on Ruddlesden-Popper perovskite microwires with broader band detection
Yongxu Yan, Zhexin Li, Zheng Lou
, Available online  
doi: 10.1088/1674-4926/44/8/082201

Recently, the two-dimensional (2D) form of Ruddlesden-Popper perovskite (RPP) has been widely studied. However, the synthesis of one-dimensional (1D) RPP is rarely reported. Here, we fabricated a photodetector based on RPP microwires (RPP-MWs) and compared it with a 2D-RPP photodetector. The results show that the RPP-MWs photodetector possesses a wider photoresponse range and higher responsivities of 233 A/W in the visible band and 30 A/W in the near-infrared (NIR) band. The analyses show that the synthesized RPP-MWs have a multi-layer, heterogeneous core-shell structure. This structure gives RPP-MWs a unique band structure, as well as abundant trap states and defect levels, which enable them to acquire better photoresponse performance. This configuration of RPP-MWs provides a new idea for the design and application of novel heterostructures.

Recently, the two-dimensional (2D) form of Ruddlesden-Popper perovskite (RPP) has been widely studied. However, the synthesis of one-dimensional (1D) RPP is rarely reported. Here, we fabricated a photodetector based on RPP microwires (RPP-MWs) and compared it with a 2D-RPP photodetector. The results show that the RPP-MWs photodetector possesses a wider photoresponse range and higher responsivities of 233 A/W in the visible band and 30 A/W in the near-infrared (NIR) band. The analyses show that the synthesized RPP-MWs have a multi-layer, heterogeneous core-shell structure. This structure gives RPP-MWs a unique band structure, as well as abundant trap states and defect levels, which enable them to acquire better photoresponse performance. This configuration of RPP-MWs provides a new idea for the design and application of novel heterostructures.
Spin injection into heavily-doped n-GaN via Schottky barrier
Zhenhao Sun, Ning Tang, Shuaiyu Chen, Fan Zhang, Haoran Fan, Shixiong Zhang, Rongxin Wang, Xi Lin, Jianping Liu, Weikun Ge, Bo Shen
, Available online  
doi: 10.1088/1674-4926/44/8/082501

Spin injection and detection in bulk GaN were investigated by performing magnetotransport measurements at low temperatures. A non-local four-terminal lateral spin valve device was fabricated with Co/GaN Schottky contacts. The spin injection efficiency of 21% was achieved at 1.7 K. It was confirmed that the thin Schottky barrier formed between the heavily n-doped GaN and Co was conducive to the direct spin tunneling, by reducing the spin scattering relaxation through the interface states.

Spin injection and detection in bulk GaN were investigated by performing magnetotransport measurements at low temperatures. A non-local four-terminal lateral spin valve device was fabricated with Co/GaN Schottky contacts. The spin injection efficiency of 21% was achieved at 1.7 K. It was confirmed that the thin Schottky barrier formed between the heavily n-doped GaN and Co was conducive to the direct spin tunneling, by reducing the spin scattering relaxation through the interface states.
State-of-the-art advances in vacancy defect engineering of graphitic carbon nitride for solar water splitting
Jie Li, Kaige Huang, Yanbin Huang, Yumin Ye, Marcin Ziółek, Zhijie Wang, Shizhong Yue, Mengmeng Ma, Jun Liu, Kong Liu, Shengchun Qu, Zhi Zhao, Yanjun Zhang, Zhanguo Wang
, Available online  
doi: 10.1088/1674-4926/44/8/081701

Developing low-cost, efficient, and stable photocatalysts is one of the most promising methods for large-scale solar water splitting. As a metal-free semiconductor material with suitable band gap, graphitic carbon nitride (g-C3N4) has attracted attention in the field of photocatalysis, which is mainly attributed to its fascinating physicochemical and photoelectronic properties. However, several inherent limitations and shortcomings—involving high recombination rate of photocarriers, insufficient reaction kinetics, and optical absorption—impede the practical applicability of g-C3N4. As an effective strategy, vacancy defect engineering has been widely used for breaking through the current limitations, considering its ability to optimize the electronic structure and surface morphology of g-C3N4 to obtain the desired photocatalytic activity. This review summarizes the recent progress of vacancy defect engineered g-C3N4 for solar water splitting. The fundamentals of solar water splitting with g-C3N4 are discussed first. We then focus on the fabrication strategies and effect of vacancy generated in g-C3N4. The advances of vacancy-modified g-C3N4 photocatalysts toward solar water splitting are then discussed. Finally, the current challenges and future opportunities of vacancy-modified g-C3N4 are summarized. This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C3N4.

Developing low-cost, efficient, and stable photocatalysts is one of the most promising methods for large-scale solar water splitting. As a metal-free semiconductor material with suitable band gap, graphitic carbon nitride (g-C3N4) has attracted attention in the field of photocatalysis, which is mainly attributed to its fascinating physicochemical and photoelectronic properties. However, several inherent limitations and shortcomings—involving high recombination rate of photocarriers, insufficient reaction kinetics, and optical absorption—impede the practical applicability of g-C3N4. As an effective strategy, vacancy defect engineering has been widely used for breaking through the current limitations, considering its ability to optimize the electronic structure and surface morphology of g-C3N4 to obtain the desired photocatalytic activity. This review summarizes the recent progress of vacancy defect engineered g-C3N4 for solar water splitting. The fundamentals of solar water splitting with g-C3N4 are discussed first. We then focus on the fabrication strategies and effect of vacancy generated in g-C3N4. The advances of vacancy-modified g-C3N4 photocatalysts toward solar water splitting are then discussed. Finally, the current challenges and future opportunities of vacancy-modified g-C3N4 are summarized. This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C3N4.
Enhanced efficiency of the Sb2Se3 thin-film solar cell by the anode passivation using an organic small molecular of TCTA
Yujie Hu, Zhixiang Chen, Yi Xiang, Chuanhui Cheng, Weifeng Liu, Weishen Zhan
, Available online  
doi: 10.1088/1674-4926/44/8/082701

Antimony selenide (Sb2Se3) is an emerging solar cell material. Here, we demonstrate that an organic small molecule of 4, 4', 4''-tris(carbazol-9-yl)-triphenylamine (TCTA) can efficiently passivate the anode interface of the Sb2Se3 solar cell. We fabricated the device by the vacuum thermal evaporation, and took ITO/TCTA (3.0 nm)/Sb2Se3 (50 nm)/C60 (5.0 nm)/Alq3 (3.0 nm)/Al as the device architecture, where Alq3 is the tris(8-hydroxyquinolinato) aluminum. By introducing a TCTA layer, the open-circuit voltage is raised from 0.36 to 0.42 V, and the power conversion efficiency is significantly improved from 3.2% to 4.3%. The TCTA layer not only inhibits the chemical reaction between the ITO and Sb2Se3 during the annealing process but it also blocks the electron diffusion from Sb2Se3 to ITO anode. The enhanced performance is mainly attributed to the suppression of the charge recombination at the anode interface.

Antimony selenide (Sb2Se3) is an emerging solar cell material. Here, we demonstrate that an organic small molecule of 4, 4', 4''-tris(carbazol-9-yl)-triphenylamine (TCTA) can efficiently passivate the anode interface of the Sb2Se3 solar cell. We fabricated the device by the vacuum thermal evaporation, and took ITO/TCTA (3.0 nm)/Sb2Se3 (50 nm)/C60 (5.0 nm)/Alq3 (3.0 nm)/Al as the device architecture, where Alq3 is the tris(8-hydroxyquinolinato) aluminum. By introducing a TCTA layer, the open-circuit voltage is raised from 0.36 to 0.42 V, and the power conversion efficiency is significantly improved from 3.2% to 4.3%. The TCTA layer not only inhibits the chemical reaction between the ITO and Sb2Se3 during the annealing process but it also blocks the electron diffusion from Sb2Se3 to ITO anode. The enhanced performance is mainly attributed to the suppression of the charge recombination at the anode interface.
Analytical model of non-uniform charge distribution within the gated region of GaN HEMTs
Amgad A. Al-Saman, Eugeny A. Ryndin, Xinchuan Zhang, Yi Pei, Fujiang Lin
, Available online  
doi: 10.1088/1674-4926/44/8/082802

A physics-based analytical expression has been developed that predicts the charge, electrical field and potential distributions along the gated region of the GaN HEMT channel. Unlike the gradual channel approximation (GCA), the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied voltage. In addition, the model can capture the influence of mobility and channel temperature on the charge distribution trend. The comparison with the hydrodynamic (HD) numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration. The analytical nature of the model allows us to reduce the computational and time cost of the simulation. Also, it can be used as a core expression to develop a complete physics-based transistor IV model without GCA limitation.

A physics-based analytical expression has been developed that predicts the charge, electrical field and potential distributions along the gated region of the GaN HEMT channel. Unlike the gradual channel approximation (GCA), the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied voltage. In addition, the model can capture the influence of mobility and channel temperature on the charge distribution trend. The comparison with the hydrodynamic (HD) numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration. The analytical nature of the model allows us to reduce the computational and time cost of the simulation. Also, it can be used as a core expression to develop a complete physics-based transistor IV model without GCA limitation.
High threshold voltage enhancement-mode GaN p-FET with Si-rich LPCVD SiNx gate insulator for high hole mobility
Liyang Zhu, Kuangli Chen, Yin Ma, Yong Cai, Chunhua Zhou, Zhaoji Li, Bo Zhang, Qi Zhou
, Available online  
doi: 10.1088/1674-4926/44/8/082801

In this work, the GaN p-MISFET with LPCVD-SiNx is studied as a gate dielectric to improve device performance. By changing the Si/N stoichiometry of SiNx, it is found that the channel hole mobility can be effectively enhanced with Si-rich SiNx gate dielectric, which leads to a respectably improved drive current of GaN p-FET. The record high channel mobility of 19.4 cm2/(V∙s) was achieved in the device featuring an Enhancement-mode channel. Benefiting from the significantly improved channel mobility, the fabricated E-mode GaN p-MISFET is capable of delivering a decent-high current of 1.6 mA/mm, while simultaneously featuring a negative threshold-voltage (VTH) of –2.3 V (defining at a stringent criteria of 10 μA/mm). The device also exhibits a well pinch-off at 0 V with low leakage current of 1 nA/mm. This suggests that a decent E-mode operation of the fabricated p-FET is obtained. In addition, the VTH shows excellent stability, while the threshold-voltage hysteresis ΔVTH is as small as 0.1 V for a gate voltage swing up to –10 V, which is among the best results reported in the literature. The results indicate that optimizing the Si/N stoichiometry of LPCVD-SiNx is a promising approach to improve the device performance of GaN p-MISFET.

In this work, the GaN p-MISFET with LPCVD-SiNx is studied as a gate dielectric to improve device performance. By changing the Si/N stoichiometry of SiNx, it is found that the channel hole mobility can be effectively enhanced with Si-rich SiNx gate dielectric, which leads to a respectably improved drive current of GaN p-FET. The record high channel mobility of 19.4 cm2/(V∙s) was achieved in the device featuring an Enhancement-mode channel. Benefiting from the significantly improved channel mobility, the fabricated E-mode GaN p-MISFET is capable of delivering a decent-high current of 1.6 mA/mm, while simultaneously featuring a negative threshold-voltage (VTH) of –2.3 V (defining at a stringent criteria of 10 μA/mm). The device also exhibits a well pinch-off at 0 V with low leakage current of 1 nA/mm. This suggests that a decent E-mode operation of the fabricated p-FET is obtained. In addition, the VTH shows excellent stability, while the threshold-voltage hysteresis ΔVTH is as small as 0.1 V for a gate voltage swing up to –10 V, which is among the best results reported in the literature. The results indicate that optimizing the Si/N stoichiometry of LPCVD-SiNx is a promising approach to improve the device performance of GaN p-MISFET.
A large-area multi-finger β-Ga2O3 MOSFET and its self-heating effect
Xuanze Zhou, Guangwei Xu, Shibing Long
, Available online  

The self-heating effect severely limits device performance and reliability. Although some studies have revealed the heat distribution of β-Ga2O3 MOSFETs under biases, those devices are all have small areas and have difficulty reflecting practical conditions. This work demonstrated a multi-finger β-Ga2O3 MOSFET with a maximum drain current of 0.5 A, electrical characteristics were measured, and the heat dissipation of the device was investigated through infrared images. The relationship between device temperature and time/bias is analyzed.

The self-heating effect severely limits device performance and reliability. Although some studies have revealed the heat distribution of β-Ga2O3 MOSFETs under biases, those devices are all have small areas and have difficulty reflecting practical conditions. This work demonstrated a multi-finger β-Ga2O3 MOSFET with a maximum drain current of 0.5 A, electrical characteristics were measured, and the heat dissipation of the device was investigated through infrared images. The relationship between device temperature and time/bias is analyzed.
2.83-kV double-layered NiO/β-Ga2O3 vertical p–n heterojunction diode with a power figure-of-merit of 5.98 GW/cm2
Tingting Han, Yuangang Wang, Yuanjie Lü, Shaobo Dun, Hongyu Liu, Aimin Bu, Zhihong Feng
, Available online  

This work demonstrates high-performance NiO/β-Ga2O3 vertical heterojunction diodes (HJDs) with double-layer junction termination extension (DL-JTE) consisting of two p-typed NiO layers with varied lengths. The bottom 60-nm p-NiO layer fully covers the β-Ga2O3 wafer, while the geometry of the upper 60-nm p-NiO layer is 10 μm larger than the square anode electrode. Compared with a single-layer JTE, the electric field concentration is inhibited by double-layer JTE structure effectively, resulting in the breakdown voltage being improved from 2020 to 2830 V. Moreover, double p-typed NiO layers allow more holes into the Ga2O3 drift layer to reduce drift resistance. The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm2. The device with DL-JTE shows a power figure-of-merit (PFOM) of 5.98 GW/cm2, which is 2.8 times larger than that of the conventional single-layer JTE structure. These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga2O3 HJDs.

This work demonstrates high-performance NiO/β-Ga2O3 vertical heterojunction diodes (HJDs) with double-layer junction termination extension (DL-JTE) consisting of two p-typed NiO layers with varied lengths. The bottom 60-nm p-NiO layer fully covers the β-Ga2O3 wafer, while the geometry of the upper 60-nm p-NiO layer is 10 μm larger than the square anode electrode. Compared with a single-layer JTE, the electric field concentration is inhibited by double-layer JTE structure effectively, resulting in the breakdown voltage being improved from 2020 to 2830 V. Moreover, double p-typed NiO layers allow more holes into the Ga2O3 drift layer to reduce drift resistance. The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm2. The device with DL-JTE shows a power figure-of-merit (PFOM) of 5.98 GW/cm2, which is 2.8 times larger than that of the conventional single-layer JTE structure. These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga2O3 HJDs.
Tunneling via surface dislocation in W/β-Ga2O3 Schottky barrier diodes
Madani Labed, Ji Young Min, Amina Ben Slim, Nouredine Sengouga, Chowdam Venkata Prasad, Sinsu Kyoung, You Seung Rim
, Available online  

In this work, W/β-Ga2O3 Schottky barrier diodes, prepared using a confined magnetic field-based sputtering method, were analyzed at different operation temperatures. Firstly, Schottky barrier height increased with increasing temperature from 100 to 300 K and reached 1.03 eV at room temperature. The ideality factor decreased with increasing temperature and it was higher than 2 at 100 K. This apparent high value was related to the tunneling effect. Secondly, the series and on-resistances decreased with increasing operation temperature. Finally, the interfacial dislocation was extracted from the tunneling current. A high dislocation density was found, which indicates the domination of tunneling through dislocation in the transport mechanism. These findings are evidently helpful in designing better performance devices.

In this work, W/β-Ga2O3 Schottky barrier diodes, prepared using a confined magnetic field-based sputtering method, were analyzed at different operation temperatures. Firstly, Schottky barrier height increased with increasing temperature from 100 to 300 K and reached 1.03 eV at room temperature. The ideality factor decreased with increasing temperature and it was higher than 2 at 100 K. This apparent high value was related to the tunneling effect. Secondly, the series and on-resistances decreased with increasing operation temperature. Finally, the interfacial dislocation was extracted from the tunneling current. A high dislocation density was found, which indicates the domination of tunneling through dislocation in the transport mechanism. These findings are evidently helpful in designing better performance devices.
Tunable luminescence of Sm3+/Tb3+ co-doped CaMoO4 phosphors synthesized by microwave-assisted heating
Wente Wu, Kwongkau Tiong, Yuwei Lee, Shengyao Hu, Yuehchien Lee, Wei Huang
, Available online  
doi: 10.1088/1674-4926/43/7/072102

We present a series of Sm3+/Tb3+ co-doped CaMoO4 phosphors synthesized by an efficient method of microwave-assisted heating. The prepared CaMoO4 samples were characterized by X-ray diffraction, photoluminescence, and Commission Internationale de l’Elcairage (CIE) chromaticity diagram. The X-ray diffraction results confirmed that all of the synthesized CaMoO4 samples are crystallized in a pure tetragonal phase. The photoluminescence spectra significantly show both red- and green emission in the synthesized Sm3+/Tb3+ co-doped CaMoO4 phosphors. It is obvious that the variations in the intensity ratio of red/green emission depend on the molar ratio of Sm3+/Tb3+ co-doping and dominate the CIE color coordinates on the chromaticity diagram. The investigations evidence that the light-emitting region of Sm3+/Tb3+ co-doped CaMoO4 phosphors can be controlled by adjusting the molar ratio of Sm3+/Tb3+ ions, acting as advanced color-tunable phosphors for white-LEDs.

We present a series of Sm3+/Tb3+ co-doped CaMoO4 phosphors synthesized by an efficient method of microwave-assisted heating. The prepared CaMoO4 samples were characterized by X-ray diffraction, photoluminescence, and Commission Internationale de l’Elcairage (CIE) chromaticity diagram. The X-ray diffraction results confirmed that all of the synthesized CaMoO4 samples are crystallized in a pure tetragonal phase. The photoluminescence spectra significantly show both red- and green emission in the synthesized Sm3+/Tb3+ co-doped CaMoO4 phosphors. It is obvious that the variations in the intensity ratio of red/green emission depend on the molar ratio of Sm3+/Tb3+ co-doping and dominate the CIE color coordinates on the chromaticity diagram. The investigations evidence that the light-emitting region of Sm3+/Tb3+ co-doped CaMoO4 phosphors can be controlled by adjusting the molar ratio of Sm3+/Tb3+ ions, acting as advanced color-tunable phosphors for white-LEDs.