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Organic bulk heterojunction enabled with nano capsules of hydrate vanadium pentaoxide layer for high responsivity self powered photodetector
Hemraj Dahiya, Anupam Agrawal, Ganesh D. Sharma, Abhishek Kumar Singh
, Available online  
doi: 10.1088/1674-4926/43/9/092302

This article demonstrates the fabrication of organic-based devices using a low-cost solution-processable technique. A blended heterojunction of chlorine substituted 2D-conjugated polymer PBDB-T-2Cl, and PC71BM supported nanocapsules hydrate vanadium penta oxides (HVO) as hole transport layer (HTL) based photodetector fabricated on an ITO coated glass substrate under ambient condition. The device forms an excellent organic junction diode with a good rectification ratio of ~200. The device has also shown excellent photodetection properties under photoconductive mode (at reverse bias) and zero bias for green light wavelength. A very high responsivity of ~6500 mA/W and high external quantum efficiency (EQE) of 1400% have been reported in the article. The proposed organic photodetector exhibits an excellent response and recovery time of ~30 and ~40 ms, respectively.

This article demonstrates the fabrication of organic-based devices using a low-cost solution-processable technique. A blended heterojunction of chlorine substituted 2D-conjugated polymer PBDB-T-2Cl, and PC71BM supported nanocapsules hydrate vanadium penta oxides (HVO) as hole transport layer (HTL) based photodetector fabricated on an ITO coated glass substrate under ambient condition. The device forms an excellent organic junction diode with a good rectification ratio of ~200. The device has also shown excellent photodetection properties under photoconductive mode (at reverse bias) and zero bias for green light wavelength. A very high responsivity of ~6500 mA/W and high external quantum efficiency (EQE) of 1400% have been reported in the article. The proposed organic photodetector exhibits an excellent response and recovery time of ~30 and ~40 ms, respectively.
Large unsaturated magnetoresistance of 2D magnetic semiconductor Fe-SnS2 homojunction
Jingzhi Fang, Huading Song, Bo Li, Ziqi Zhou, Juehan Yang, Benchuan Lin, Zhimin Liao, Zhongming Wei
, Available online  
doi: 10.1088/1674-4926/43/9/092501

A magnetic semiconductor whose electronic charge and spin can be regulated together will be an important component of future spintronic devices. Here, we construct a two-dimensional (2D) Fe doped SnS2 (Fe-SnS2) homogeneous junction and investigate its electromagnetic transport feature. The Fe-SnS2 homojunction device showed large positive and unsaturated magnetoresistance (MR) of 1800% in the parallel magnetic field and 600% in the vertical magnetic field, indicating an obvious anisotropic MR feature. In contrast, The MR of Fe-SnS2 homojunction is much larger than the pure diamagnetic SnS2 and most 2D materials. The application of a gate voltage can regulate the MR effect of Fe-SnS2 homojunction devices. Moreover, the stability of Fe-SnS2 in air has great application potential. Our Fe-SnS2 homojunction has a significant potential in future magnetic memory applications.

A magnetic semiconductor whose electronic charge and spin can be regulated together will be an important component of future spintronic devices. Here, we construct a two-dimensional (2D) Fe doped SnS2 (Fe-SnS2) homogeneous junction and investigate its electromagnetic transport feature. The Fe-SnS2 homojunction device showed large positive and unsaturated magnetoresistance (MR) of 1800% in the parallel magnetic field and 600% in the vertical magnetic field, indicating an obvious anisotropic MR feature. In contrast, The MR of Fe-SnS2 homojunction is much larger than the pure diamagnetic SnS2 and most 2D materials. The application of a gate voltage can regulate the MR effect of Fe-SnS2 homojunction devices. Moreover, the stability of Fe-SnS2 in air has great application potential. Our Fe-SnS2 homojunction has a significant potential in future magnetic memory applications.
Superfluorescence from halide perovskite nanocrystal superlattices
Liang Chu, Lixiu Zhang, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/10/100202

Polarization sensitive photodetector based on quasi-1D ZrSe3
Xingang Wang, Tao Xiong, Kaiyao Xin, Juehan Yang, Yueyang Liu, Zeping Zhao, Jianguo Liu, Zhongming Wei
, Available online  
doi: 10.1088/1674-4926/43/10/102001

The in-plane anisotropy of transition metal trichalcogenides (MX3) has a significant impact on the molding of materials and MX3 is a perfect choice for polarized photodetectors. In this study, the crystal structure, optical and optoelectronic anisotropy of one kind of quasi-one-dimensional (1D) semiconductors, ZrSe3, are systematically investigated through experiments and theoretical studies. The ZrSe3-based photodetector shows impressive wide spectral response from ultraviolet (UV) to near infrared (NIR) and exhibits great optoelectrical properties with photoresponsivity of 11.9 mA/W and detectivity of ~106 at 532 nm. Moreover, the dichroic ratio of ZrSe3-based polarized photodetector is around 1.1 at 808 nm. This study suggests that ZrSe3 has potential in optoelectronic applications and polarization detectors.

The in-plane anisotropy of transition metal trichalcogenides (MX3) has a significant impact on the molding of materials and MX3 is a perfect choice for polarized photodetectors. In this study, the crystal structure, optical and optoelectronic anisotropy of one kind of quasi-one-dimensional (1D) semiconductors, ZrSe3, are systematically investigated through experiments and theoretical studies. The ZrSe3-based photodetector shows impressive wide spectral response from ultraviolet (UV) to near infrared (NIR) and exhibits great optoelectrical properties with photoresponsivity of 11.9 mA/W and detectivity of ~106 at 532 nm. Moreover, the dichroic ratio of ZrSe3-based polarized photodetector is around 1.1 at 808 nm. This study suggests that ZrSe3 has potential in optoelectronic applications and polarization detectors.
A low-power high-quality CMOS image sensor using 1.5 V 4T pinned photodiode and dual-CDS column-parallel single-slope ADC
Wenjing Xu, Jie Chen, Zhangqu Kuang, Li Zhou, Ming Chen, Chengbin Zhang
, Available online  
doi: 10.1088/1674-4926/43/8/082401

This paper presents a low-power high-quality CMOS image sensor (CIS) using 1.5 V 4T pinned photodiode (4T-PPD) and dual correlated double sampling (dual-CDS) column-parallel single-slope ADC. A five-finger shaped pixel layer is proposed to solve image lag caused by low-voltage 4T-PPD. Dual-CDS is used to reduce random noise and the nonuniformity between columns. Dual-mode counting method is proposed to improve circuit robustness. A prototype sensor was fabricated using a 0.11 µm CMOS process. Measurement results show that the lag of the five-finger shaped pixel is reduced by 80% compared with the conventional rectangular pixel, the chip power consumption is only 36 mW, the dynamic range is 67.3 dB, the random noise is only 1.55 erms, and the figure-of-merit is only 1.98 e·nJ, thus realizing low-power and high-quality imaging.

This paper presents a low-power high-quality CMOS image sensor (CIS) using 1.5 V 4T pinned photodiode (4T-PPD) and dual correlated double sampling (dual-CDS) column-parallel single-slope ADC. A five-finger shaped pixel layer is proposed to solve image lag caused by low-voltage 4T-PPD. Dual-CDS is used to reduce random noise and the nonuniformity between columns. Dual-mode counting method is proposed to improve circuit robustness. A prototype sensor was fabricated using a 0.11 µm CMOS process. Measurement results show that the lag of the five-finger shaped pixel is reduced by 80% compared with the conventional rectangular pixel, the chip power consumption is only 36 mW, the dynamic range is 67.3 dB, the random noise is only 1.55 erms, and the figure-of-merit is only 1.98 e·nJ, thus realizing low-power and high-quality imaging.
Valley dynamics of different excitonic states in monolayer WSe2 grown by molecular beam epitaxy
Shengmin Hu, Jialiang Ye, Ruiqi Liu, Xinhui Zhang
, Available online  
doi: 10.1088/1674-4926/43/8/082001

Monolayer transition-metal dichalcogenides possess rich excitonic physics and unique valley-contrasting optical selection rule, and offer a great platform for long spin/valley lifetime engineering and the associated spin/valleytronics exploration. Using two-color time-resolved Kerr rotation and time-resolved reflectivity spectroscopy, we investigate the spin/valley dynamics of different excitonic states in monolayer WSe2 grown by molecular beam epitaxy. With fine tuning of the photon energy of both pump and probe beams, the valley relaxation process for the neutral excitons and trions is found to be remarkably different—their characteristic spin/valley lifetimes vary from picoseconds to nanoseconds, respectively. The observed long trion spin lifetime of > 2.0 ns is discussed to be associated with the dark trion states, which is evidenced by the photon-energy dependent valley polarization relaxation. Our results also reveal that valley depolarization for these different excitonic states is intimately connected with the strong Coulomb interaction when the optical excitation energy is above the exciton resonance.

Monolayer transition-metal dichalcogenides possess rich excitonic physics and unique valley-contrasting optical selection rule, and offer a great platform for long spin/valley lifetime engineering and the associated spin/valleytronics exploration. Using two-color time-resolved Kerr rotation and time-resolved reflectivity spectroscopy, we investigate the spin/valley dynamics of different excitonic states in monolayer WSe2 grown by molecular beam epitaxy. With fine tuning of the photon energy of both pump and probe beams, the valley relaxation process for the neutral excitons and trions is found to be remarkably different—their characteristic spin/valley lifetimes vary from picoseconds to nanoseconds, respectively. The observed long trion spin lifetime of > 2.0 ns is discussed to be associated with the dark trion states, which is evidenced by the photon-energy dependent valley polarization relaxation. Our results also reveal that valley depolarization for these different excitonic states is intimately connected with the strong Coulomb interaction when the optical excitation energy is above the exciton resonance.
Interlocked MXene/rGO aerogel with excellent mechanical stability for a health-monitoring device
Shufang Zhao, Wenhao Ran, Lili Wang, Guozhen Shen
, Available online  
doi: 10.1088/1674-4926/43/8/082601

Two-dimensional (2D) materials have attracted considerable interest thanks to their unique electronic/physical–chemical characteristics and their potential for use in a large variety of sensing applications. However, few-layered nanosheets tend to agglomerate owing to van der Waals forces, which obstruct internal nanoscale transport channels, resulting in low electrochemical activity and restricting their use for sensing purposes. Here, a hybrid MXene/rGO aerogel with a three-dimensional (3D) interlocked network was fabricated via a freeze-drying method. The porous MXene/rGO aerogel has a lightweight and hierarchical porous architecture, which can be compressed and expanded several times without breaking. Additionally, a flexible pressure sensor that uses the aerogel as the sensitive layer has a wide response range of approximately 0–40 kPa and a considerable response within this range, averaging approximately 61.49 kPa–1. The excellent sensing performance endows it with a broad range of applications, including human-computer interfaces and human health monitoring.

Two-dimensional (2D) materials have attracted considerable interest thanks to their unique electronic/physical–chemical characteristics and their potential for use in a large variety of sensing applications. However, few-layered nanosheets tend to agglomerate owing to van der Waals forces, which obstruct internal nanoscale transport channels, resulting in low electrochemical activity and restricting their use for sensing purposes. Here, a hybrid MXene/rGO aerogel with a three-dimensional (3D) interlocked network was fabricated via a freeze-drying method. The porous MXene/rGO aerogel has a lightweight and hierarchical porous architecture, which can be compressed and expanded several times without breaking. Additionally, a flexible pressure sensor that uses the aerogel as the sensitive layer has a wide response range of approximately 0–40 kPa and a considerable response within this range, averaging approximately 61.49 kPa–1. The excellent sensing performance endows it with a broad range of applications, including human-computer interfaces and human health monitoring.
Simulation of MoS2 stacked nanosheet field effect transistor
Yang Shen, He Tian, Tianling Ren
, Available online  
doi: 10.1088/1674-4926/43/8/082002

Transition metal dichalcogenides are nowadays appealing to researchers for their excellent electronic properties. Vertical stacked nanosheet FET (NSFET) based on MoS2 are proposed and studied by Poisson equation solver coupled with semi-classical quantum correction model implemented in Sentaurus workbench. It is found that, the 2D stacked NSFET can largely suppress short channel effects with improved subthreshold swing and drain induced barrier lowering, due to the excellent electrostatics of 2D MoS2. In addition, small-signal capacitance is extracted and analyzed. The MoS2 based NSFET shows great potential to enable next generation electronics.

Transition metal dichalcogenides are nowadays appealing to researchers for their excellent electronic properties. Vertical stacked nanosheet FET (NSFET) based on MoS2 are proposed and studied by Poisson equation solver coupled with semi-classical quantum correction model implemented in Sentaurus workbench. It is found that, the 2D stacked NSFET can largely suppress short channel effects with improved subthreshold swing and drain induced barrier lowering, due to the excellent electrostatics of 2D MoS2. In addition, small-signal capacitance is extracted and analyzed. The MoS2 based NSFET shows great potential to enable next generation electronics.
Ni/Pd-based ohmic contacts to p-GaN through p-InGaN/p+-GaN contacting layers
Minglong Zhang, Masao Ikeda, Siyi Huang, Jianping Liu, Jianjun Zhu, Shuming Zhang, Hui Yang
, Available online  
doi: 10.1088/1674-4926/43/9/092803

Specific contact resistance $ {\rho }_{\mathrm{c}} $ to p-GaN was measured for various structures of Ni/Pd-based metals and thin (20–30 nm thick) p-InGaN/p+-GaN contacting layers. The effects of surface chemical treatment and annealing temperature were examined. The optimal annealing temperature was determined to be 550 °C, above which the sheet resistance of the samples degraded considerably, suggesting that undesirable alloying had occurred. Pd-containing metal showed ~35% lower $ {\rho }_{\mathrm{c}} $ compared to that of single Ni. Very thin (2–3.5 nm thick) p-InGaN contacting layers grown on 20–25 nm thick p+-GaN layers exhibited one to two orders of magnitude smaller values of $ {\rho }_{\mathrm{c}} $ compared to that of p+-GaN without p-InGaN. The current density dependence of $ {\rho }_{\mathrm{c}} $, which is indicative of nonlinearity in current-voltage relation, was also examined. The lowest $ {\rho }_{\mathrm{c}} $ achieved through this study was 4.9 × 10–5 Ω·cm2 @ J = 3.4 kA/cm2.

Specific contact resistance $ {\rho }_{\mathrm{c}} $ to p-GaN was measured for various structures of Ni/Pd-based metals and thin (20–30 nm thick) p-InGaN/p+-GaN contacting layers. The effects of surface chemical treatment and annealing temperature were examined. The optimal annealing temperature was determined to be 550 °C, above which the sheet resistance of the samples degraded considerably, suggesting that undesirable alloying had occurred. Pd-containing metal showed ~35% lower $ {\rho }_{\mathrm{c}} $ compared to that of single Ni. Very thin (2–3.5 nm thick) p-InGaN contacting layers grown on 20–25 nm thick p+-GaN layers exhibited one to two orders of magnitude smaller values of $ {\rho }_{\mathrm{c}} $ compared to that of p+-GaN without p-InGaN. The current density dependence of $ {\rho }_{\mathrm{c}} $, which is indicative of nonlinearity in current-voltage relation, was also examined. The lowest $ {\rho }_{\mathrm{c}} $ achieved through this study was 4.9 × 10–5 Ω·cm2 @ J = 3.4 kA/cm2.
Defect passivation with potassium trifluoroborate for efficient spray-coated perovskite solar cells in air
Chen Gao, Hui Wang, Pang Wang, Jinlong Cai, Yuandong Sun, Cong Yu, Teng Li, Xiaoshuai Zhang, Dan Liu, Tao Wang
, Available online  
doi: 10.1088/1674-4926/43/9/092201

Defects as non-radiative recombination centers hinder the further efficiency improvements of perovskite solar cells (PSCs). Additive engineering has been demonstrated to be an effective method for defect passivation in perovskite films. Here, we employed (4-methoxyphenyl) potassium trifluoroborate (C7H7BF3KO) with ${{\rm{BF}}_3^-}$ and K+ functional groups to passivate spray-coated (FAPbI3)x(MAPbBr3)1–x perovskite and eliminate hysteresis. It is shown that the F of ${{\rm{BF}}_3^-}$ can form hydrogen bonds with the H atom in the amino group of MA+/FA+ ions of perovskite, thus reducing the generation of MA+/FA+ vacancies and improving device efficiency. Meanwhile, K+ and reduced MA+/FA+ vacancies can inhibit ion migration, thereby eliminating hysteresis. With the aid of C7H7BF3KO, we obtained hysteresis-free PSCs with the maximum efficiency of 19.5% by spray-coating in air. Our work demonstrates that additive engineering is promising to improve the performance of spray-coated PSCs.

Defects as non-radiative recombination centers hinder the further efficiency improvements of perovskite solar cells (PSCs). Additive engineering has been demonstrated to be an effective method for defect passivation in perovskite films. Here, we employed (4-methoxyphenyl) potassium trifluoroborate (C7H7BF3KO) with ${{\rm{BF}}_3^-}$ and K+ functional groups to passivate spray-coated (FAPbI3)x(MAPbBr3)1–x perovskite and eliminate hysteresis. It is shown that the F of ${{\rm{BF}}_3^-}$ can form hydrogen bonds with the H atom in the amino group of MA+/FA+ ions of perovskite, thus reducing the generation of MA+/FA+ vacancies and improving device efficiency. Meanwhile, K+ and reduced MA+/FA+ vacancies can inhibit ion migration, thereby eliminating hysteresis. With the aid of C7H7BF3KO, we obtained hysteresis-free PSCs with the maximum efficiency of 19.5% by spray-coating in air. Our work demonstrates that additive engineering is promising to improve the performance of spray-coated PSCs.
Technologies and applications of silicon-based micro-optical electromechanical systems: A brief review
Shanshan Chen, Yongyue Zhang, Xiaorong Hong, Jiafang Li
, Available online  
doi: 10.1088/1674-4926/43/8/081301

Micro-optical electromechanical systems (MOEMS) combine the merits of micro-electromechanical systems (MEMS) and micro-optics to enable unique optical functions for a wide range of advanced applications. Using simple external electromechanical control methods, such as electrostatic, magnetic or thermal effects, Si-based MOEMS can achieve precise dynamic optical modulation. In this paper, we will briefly review the technologies and applications of Si-based MOEMS. Their basic working principles, advantages, general materials and micromachining fabrication technologies are introduced concisely, followed by research progress of advanced Si-based MOEMS devices, including micromirrors/micromirror arrays, micro-spectrometers, and optical/photonic switches. Owing to the unique advantages of Si-based MOEMS in spatial light modulation and high-speed signal processing, they have several promising applications in optical communications, digital light processing, and optical sensing. Finally, future research and development prospects of Si-based MOEMS are discussed.

Micro-optical electromechanical systems (MOEMS) combine the merits of micro-electromechanical systems (MEMS) and micro-optics to enable unique optical functions for a wide range of advanced applications. Using simple external electromechanical control methods, such as electrostatic, magnetic or thermal effects, Si-based MOEMS can achieve precise dynamic optical modulation. In this paper, we will briefly review the technologies and applications of Si-based MOEMS. Their basic working principles, advantages, general materials and micromachining fabrication technologies are introduced concisely, followed by research progress of advanced Si-based MOEMS devices, including micromirrors/micromirror arrays, micro-spectrometers, and optical/photonic switches. Owing to the unique advantages of Si-based MOEMS in spatial light modulation and high-speed signal processing, they have several promising applications in optical communications, digital light processing, and optical sensing. Finally, future research and development prospects of Si-based MOEMS are discussed.
Failure pathways of perovskite solar cells in space
Baoze Liu, Lixiu Zhang, Yan Jiang, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/10/100201

RF characterization of InP double heterojunction bipolar transistors on a flexible substrate under bending conditions
Lishu Wu, Jiayun Dai, Yuechan Kong, Tangsheng Chen, Tong Zhang
, Available online  
doi: 10.1088/1674-4926/43/9/092601

This letter presents the fabrication of InP double heterojunction bipolar transistors (DHBTs) on a 3-inch flexible substrate with various thickness values of the benzocyclobutene (BCB) adhesive bonding layer, the corresponding thermal resistance of the InP DHBT on flexible substrate is also measured and calculated. InP DHBT on a flexible substrate with 100 nm BCB obtains cut-off frequency fT = 358 GHz and maximum oscillation frequency fMAX = 530 GHz. Moreover, the frequency performance of the InP DHBT on flexible substrates at different bending radii are compared. It is shown that the bending strain has little effect on the frequency characteristics (less than 8.5%), and these bending tests prove that InP DHBT has feasible flexibility.

This letter presents the fabrication of InP double heterojunction bipolar transistors (DHBTs) on a 3-inch flexible substrate with various thickness values of the benzocyclobutene (BCB) adhesive bonding layer, the corresponding thermal resistance of the InP DHBT on flexible substrate is also measured and calculated. InP DHBT on a flexible substrate with 100 nm BCB obtains cut-off frequency fT = 358 GHz and maximum oscillation frequency fMAX = 530 GHz. Moreover, the frequency performance of the InP DHBT on flexible substrates at different bending radii are compared. It is shown that the bending strain has little effect on the frequency characteristics (less than 8.5%), and these bending tests prove that InP DHBT has feasible flexibility.
Identification of subsurface damage of 4H-SiC wafers by combining photo-chemical etching and molten-alkali etching
Wenhao Geng, Guang Yang, Xuqing Zhang, Xi Zhang, Yazhe Wang, Lihui Song, Penglei Chen, Yiqiang Zhang, Xiaodong Pi, Deren Yang, Rong Wang
, Available online  

In this work, we propose to reveal subsurface damage (SSD) in 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching. Under UV illumination, SSD acts as a photoluminescence-black defect. The selective photo-chemical etching reveals SSD as ridge-like defects. It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion. The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines, which are typical features of underlying scratches. This means that the underlying scratches under mechanical stress gives rise to the formation of SSD in 4H-SiC wafers. SSD is incorporated into 4H-SiC wafers during the lapping, rather than the chemical mechanical polishing (CMP).

In this work, we propose to reveal subsurface damage (SSD) in 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching. Under UV illumination, SSD acts as a photoluminescence-black defect. The selective photo-chemical etching reveals SSD as ridge-like defects. It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion. The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines, which are typical features of underlying scratches. This means that the underlying scratches under mechanical stress gives rise to the formation of SSD in 4H-SiC wafers. SSD is incorporated into 4H-SiC wafers during the lapping, rather than the chemical mechanical polishing (CMP).
COF-based electrochromic materials and devices
Yunye Wang, Zuo Xiao, Shanxin Xiong, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/9/090202

An E-band CMOS frequency quadrupler with 1.7-dBm output power and 45-dB fundamental suppression
Xiaofei Liao, Dixian Zhao, Xiaohu You
, Available online  
doi: 10.1088/1674-4926/43/9/092401

This paper presents an E-band frequency quadrupler in 40-nm CMOS technology. The circuit employs two push–push frequency doublers and two single-stage neutralized amplifiers. The pseudo-differential class-B biased cascode topology is adopted for the frequency doubler, which improves the reverse isolation and the conversion gain. Neutralization technique is applied to increase the stability and the power gain of the amplifiers simultaneously. The stacked transformers are used for single-ended-to-differential transformation as well as output bandpass filtering. The output bandpass filter enhances the 4th-harmonic output power, while rejecting the undesired harmonics, especially the 2th harmonic. The core chip is 0.23 mm2 in size and consumes 34 mW. The measured 4th harmonic achieves a maximum output power of 1.7 dBm with a peak conversion gain of 3.4 dB at 76 GHz. The fundamental and 2nd-harmonic suppressions of over 45 and 20 dB are achieved for the spectrum from 74 to 82 GHz, respectively.

This paper presents an E-band frequency quadrupler in 40-nm CMOS technology. The circuit employs two push–push frequency doublers and two single-stage neutralized amplifiers. The pseudo-differential class-B biased cascode topology is adopted for the frequency doubler, which improves the reverse isolation and the conversion gain. Neutralization technique is applied to increase the stability and the power gain of the amplifiers simultaneously. The stacked transformers are used for single-ended-to-differential transformation as well as output bandpass filtering. The output bandpass filter enhances the 4th-harmonic output power, while rejecting the undesired harmonics, especially the 2th harmonic. The core chip is 0.23 mm2 in size and consumes 34 mW. The measured 4th harmonic achieves a maximum output power of 1.7 dBm with a peak conversion gain of 3.4 dB at 76 GHz. The fundamental and 2nd-harmonic suppressions of over 45 and 20 dB are achieved for the spectrum from 74 to 82 GHz, respectively.
Perovskite nanocrystals for light-emitting diodes
Xinyi Mei, Lixiu Zhang, Xiaoliang Zhang, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/9/090201

Influence of epitaxial layer structure and cell structure on electrical performance of 6.5 kV SiC MOSFET
Lixin Tian, Zechen Du, Rui Liu, Xiping Niu, Wenting Zhang, Yunlai An, Zhanwei Shen, Fei Yang, Xiaoguang Wei
, Available online  
doi: 10.1088/1674-4926/43/8/082802

Silicon carbide (SiC) material features a wide bandgap and high critical breakdown field intensity. It also plays an important role in the high efficiency and miniaturization of power electronic equipment. It is an ideal choice for new power electronic devices, especially in smart grids and high-speed trains. In the medium and high voltage fields, SiC devices with a blocking voltage of more than 6.5 kV will have a wide range of applications. In this paper, we study the influence of epitaxial material properties on the static characteristics of 6.5 kV SiC MOSFET. 6.5 kV SiC MOSFETs with different channel lengths and JFET region widths are manufactured on three wafers and analyzed. The FN tunneling of gate oxide, HTGB and HTRB tests are performed and provide data support for the industrialization process for medium/high voltage SiC MOSFETs.

Silicon carbide (SiC) material features a wide bandgap and high critical breakdown field intensity. It also plays an important role in the high efficiency and miniaturization of power electronic equipment. It is an ideal choice for new power electronic devices, especially in smart grids and high-speed trains. In the medium and high voltage fields, SiC devices with a blocking voltage of more than 6.5 kV will have a wide range of applications. In this paper, we study the influence of epitaxial material properties on the static characteristics of 6.5 kV SiC MOSFET. 6.5 kV SiC MOSFETs with different channel lengths and JFET region widths are manufactured on three wafers and analyzed. The FN tunneling of gate oxide, HTGB and HTRB tests are performed and provide data support for the industrialization process for medium/high voltage SiC MOSFETs.
Compositional engineering for lead halide perovskite solar cells
Haoxin Wang, Lixiu Zhang, Ming Cheng, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/8/080202

Growth and characterization of β-Ga2O3 thin films grown on off-angled Al2O3 substrates by metal-organic chemical vapor deposition
Yabao Zhang, Jun Zheng, Peipei Ma, Xueyi Zheng, Zhi Liu, Yuhua Zuo, Chuanbo Li, Buwen Cheng
, Available online  
doi: 10.1088/1674-4926/43/9/092801

Beta-gallium oxide (β-Ga2O3) thin films were deposited on c-plane (0001) sapphire substrates with different mis-cut angles along <$11\bar{2}0$> by metal-organic chemical vapor deposition (MOCVD). The structural properties and surface morphology of as-grown β-Ga2O3 thin films were investigated in detail. It was found that by using thin buffer layer and mis-cut substrate technology, the full width at half maximum (FWHM) of the ($ \bar{2}01$) diffraction peak of the β-Ga2O3 film is decreased from 2° on c-plane (0001) Al2O3 substrate to 0.64° on an 8° off-angled c-plane (0001) Al2O3 substrate. The surface root-mean-square (RMS) roughness can also be improved greatly and the value is 1.27 nm for 8° off-angled c-plane (0001) Al2O3 substrate. Room temperature photoluminescence (PL) was observed, which was attributed to the self-trapped excitons formed by oxygen and gallium vacancies in the film. The ultraviolet–blue PL intensity related with oxygen and gallium vacancies is decreased with the increasing mis-cut angle, which is in agreement with the improved crystal quality measured by high resolution X-ray diffraction (HR-XRD). The present results provide a route for growing high quality β-Ga2O3 film on Al2O3 substrate.

Beta-gallium oxide (β-Ga2O3) thin films were deposited on c-plane (0001) sapphire substrates with different mis-cut angles along <$11\bar{2}0$> by metal-organic chemical vapor deposition (MOCVD). The structural properties and surface morphology of as-grown β-Ga2O3 thin films were investigated in detail. It was found that by using thin buffer layer and mis-cut substrate technology, the full width at half maximum (FWHM) of the ($ \bar{2}01$) diffraction peak of the β-Ga2O3 film is decreased from 2° on c-plane (0001) Al2O3 substrate to 0.64° on an 8° off-angled c-plane (0001) Al2O3 substrate. The surface root-mean-square (RMS) roughness can also be improved greatly and the value is 1.27 nm for 8° off-angled c-plane (0001) Al2O3 substrate. Room temperature photoluminescence (PL) was observed, which was attributed to the self-trapped excitons formed by oxygen and gallium vacancies in the film. The ultraviolet–blue PL intensity related with oxygen and gallium vacancies is decreased with the increasing mis-cut angle, which is in agreement with the improved crystal quality measured by high resolution X-ray diffraction (HR-XRD). The present results provide a route for growing high quality β-Ga2O3 film on Al2O3 substrate.
Electrical and optical properties of hydrogen plasma treated β-Ga2O3 thin films
Qian Jiang, Junhua Meng, Yiming Shi, Zhigang Yin, Jingren Chen, Jing Zhang, Jinliang Wu, Xingwang Zhang
, Available online  
doi: 10.1088/1674-4926/43/9/092802

The behavior of H in β-Ga2O3 is of substantial interest because it is a common residual impurity that is present in β-Ga2O3, regardless of the synthesis methods. Herein, we report the influences of H-plasma exposure on the electric and optical properties of the heteroepitaxial β-Ga2O3 thin films grown on sapphire substrates by chemical vapor deposition. The results indicate that the H incorporation leads to a significantly increased electrical conductivity, a greatly reduced defect-related photoluminescence emission, and a slightly enhanced transmittance, while it has little effect on the crystalline quality of the β-Ga2O3 films. The significant changes in the electrical and optical properties of β-Ga2O3 may originate from the formation of shallow donor states and the passivation the defects by the incorporated H. Temperature dependent electrical properties of the H-incorporated β-Ga2O3 films are also investigated, and the dominant scattering mechanisms at various temperatures are discussed.

The behavior of H in β-Ga2O3 is of substantial interest because it is a common residual impurity that is present in β-Ga2O3, regardless of the synthesis methods. Herein, we report the influences of H-plasma exposure on the electric and optical properties of the heteroepitaxial β-Ga2O3 thin films grown on sapphire substrates by chemical vapor deposition. The results indicate that the H incorporation leads to a significantly increased electrical conductivity, a greatly reduced defect-related photoluminescence emission, and a slightly enhanced transmittance, while it has little effect on the crystalline quality of the β-Ga2O3 films. The significant changes in the electrical and optical properties of β-Ga2O3 may originate from the formation of shallow donor states and the passivation the defects by the incorporated H. Temperature dependent electrical properties of the H-incorporated β-Ga2O3 films are also investigated, and the dominant scattering mechanisms at various temperatures are discussed.
Strict non-blocking four-port optical router for mesh photonic network-on-chip
Yuhao Xia, Shanglin Yang, Jiaqi Niu, Xin Fu, Lin Yang
, Available online  
doi: 10.1088/1674-4926/43/9/092301

We report a strict non-blocking four-port optical router that is used for a mesh photonic network-on-chip on a silicon-on-insulator platform. The router consists of eight silicon microring switches that are tuned by the thermo-optic effect. For each tested rousting state, the signal-to-noise ratio of the optical router is larger than 13.8 dB at the working wavelength. The routing functionality of the device is verified. We perform 40 Gbps nonreturn to zero code data transmission on its 12 optical links. Meanwhile, data transmission using wavelength division multiplexing on eight channels in the C band (from 1525 to 1565 nm) has been adopted to increase the communication capacity. The optical router’s average energy efficiency is 25.52 fJ/bit. The rising times (10% to 90%) of the eight optical switch elements are less than 10 µs and the falling times (90%–10%) are less than 20 µs.

We report a strict non-blocking four-port optical router that is used for a mesh photonic network-on-chip on a silicon-on-insulator platform. The router consists of eight silicon microring switches that are tuned by the thermo-optic effect. For each tested rousting state, the signal-to-noise ratio of the optical router is larger than 13.8 dB at the working wavelength. The routing functionality of the device is verified. We perform 40 Gbps nonreturn to zero code data transmission on its 12 optical links. Meanwhile, data transmission using wavelength division multiplexing on eight channels in the C band (from 1525 to 1565 nm) has been adopted to increase the communication capacity. The optical router’s average energy efficiency is 25.52 fJ/bit. The rising times (10% to 90%) of the eight optical switch elements are less than 10 µs and the falling times (90%–10%) are less than 20 µs.
Demonstration of 4H-SiC CMOS digital IC gates based on the mainstream 6-inch wafer processing technique
Tongtong Yang, Yan Wang, Ruifeng Yue
, Available online  
doi: 10.1088/1674-4926/43/8/082801

In this article, the design, fabrication and characterization of silicon carbide (SiC) complementary-metal-oxide-semiconductor (CMOS)-based integrated circuits (ICs) are presented. A metal interconnect strategy is proposed to fabricate the fundamental N-channel MOS (NMOS) and P-channel MOS (PMOS) devices that are required for the CMOS circuit configuration. Based on the mainstream 6-inch SiC wafer processing technology, the simultaneous fabrication of SiC CMOS ICs and power MOSFET is realized. Fundamental gates, such as inverter and NAND gates, are fabricated and tested. The measurement results show that the inverter and NAND gates function well. The calculated low-to-high delay (low-to-high output transition) and high-to-low delay (high-to-low output transition) are 49.9 and 90 ns, respectively.

In this article, the design, fabrication and characterization of silicon carbide (SiC) complementary-metal-oxide-semiconductor (CMOS)-based integrated circuits (ICs) are presented. A metal interconnect strategy is proposed to fabricate the fundamental N-channel MOS (NMOS) and P-channel MOS (PMOS) devices that are required for the CMOS circuit configuration. Based on the mainstream 6-inch SiC wafer processing technology, the simultaneous fabrication of SiC CMOS ICs and power MOSFET is realized. Fundamental gates, such as inverter and NAND gates, are fabricated and tested. The measurement results show that the inverter and NAND gates function well. The calculated low-to-high delay (low-to-high output transition) and high-to-low delay (high-to-low output transition) are 49.9 and 90 ns, respectively.
Review in situ transmission electron microscope with machine learning
Zhiheng Cheng, Chaolun Wang, Xing Wu, Junhao Chu
, Available online  
doi: 10.1088/1674-4926/43/8/081001

Advanced electronic materials are the fundamental building blocks of integrated circuits (ICs). The microscale properties of electronic materials (e.g., crystal structures, defects, and chemical properties) can have a considerable impact on the performance of ICs. Comprehensive characterization and analysis of the material in real time with high-spatial resolution are indispensable. In situ transmission electron microscope (TEM) with atomic resolution and external field can be applied as a physical simulation platform to study the evolution of electronic material in working conditions. The high-speed camera of the in situ TEM generates a high frame rate video, resulting in a large dataset that is beyond the data processing ability of researchers using the traditional method. To overcome this challenge, many works on automated TEM analysis by using machine-learning algorithm have been proposed. In this review, we introduce the technical evolution of TEM data acquisition, including analysis, and we summarize the application of machine learning to TEM data analysis in the aspects of morphology, defect, structure, and spectra. Some of the challenges of automated TEM analysis are given in the conclusion.

Advanced electronic materials are the fundamental building blocks of integrated circuits (ICs). The microscale properties of electronic materials (e.g., crystal structures, defects, and chemical properties) can have a considerable impact on the performance of ICs. Comprehensive characterization and analysis of the material in real time with high-spatial resolution are indispensable. In situ transmission electron microscope (TEM) with atomic resolution and external field can be applied as a physical simulation platform to study the evolution of electronic material in working conditions. The high-speed camera of the in situ TEM generates a high frame rate video, resulting in a large dataset that is beyond the data processing ability of researchers using the traditional method. To overcome this challenge, many works on automated TEM analysis by using machine-learning algorithm have been proposed. In this review, we introduce the technical evolution of TEM data acquisition, including analysis, and we summarize the application of machine learning to TEM data analysis in the aspects of morphology, defect, structure, and spectra. Some of the challenges of automated TEM analysis are given in the conclusion.
Research on quantum well intermixing of 680 nm AlGaInP/GaInP semiconductor lasers induced by composited Si–Si3N4 dielectric layer
Tianjiang He, Suping Liu, Wei Li, Cong Xiong, Nan Lin, Li Zhong, Xiaoyu Ma
, Available online  
doi: 10.1088/1674-4926/43/8/082301

The optical catastrophic damage that usually occurs at the cavity surface of semiconductor lasers has become the main bottleneck affecting the improvement of laser output power and long-term reliability. To improve the output power of 680 nm AlGaInP/GaInP quantum well red semiconductor lasers, Si–Si3N4 composited dielectric layers are used to induce its quantum wells to be intermixed at the cavity surface to make a non-absorption window. Si with a thickness of 100 nm and Si3N4 with a thickness of 100 nm were grown on the surface of the epitaxial wafer by magnetron sputtering and PECVD as diffusion source and driving source, respectively. Compared with traditional Si impurity induced quantum well intermixing, this paper realizes the blue shift of 54.8 nm in the nonabsorbent window region at a lower annealing temperature of 600 °C and annealing time of 10 min. Under this annealing condition, the wavelength of the gain luminescence region basically does not shift to short wavelength, and the surface morphology of the whole epitaxial wafer remains fine after annealing. The application of this process condition can reduce the difficulty of production and save cost, which provides an effective method for upcoming fabrication.

The optical catastrophic damage that usually occurs at the cavity surface of semiconductor lasers has become the main bottleneck affecting the improvement of laser output power and long-term reliability. To improve the output power of 680 nm AlGaInP/GaInP quantum well red semiconductor lasers, Si–Si3N4 composited dielectric layers are used to induce its quantum wells to be intermixed at the cavity surface to make a non-absorption window. Si with a thickness of 100 nm and Si3N4 with a thickness of 100 nm were grown on the surface of the epitaxial wafer by magnetron sputtering and PECVD as diffusion source and driving source, respectively. Compared with traditional Si impurity induced quantum well intermixing, this paper realizes the blue shift of 54.8 nm in the nonabsorbent window region at a lower annealing temperature of 600 °C and annealing time of 10 min. Under this annealing condition, the wavelength of the gain luminescence region basically does not shift to short wavelength, and the surface morphology of the whole epitaxial wafer remains fine after annealing. The application of this process condition can reduce the difficulty of production and save cost, which provides an effective method for upcoming fabrication.
Singlet fission and its application in organic solar cells
Yamin Zhang, Zuo Xiao, Liming Ding, Hao-Li Zhang
, Available online  
doi: 10.1088/1674-4926/43/8/080201

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.