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
Hybrid C8-BTBT/InGaAs nanowire heterojunction for artificial photosynaptic transistors
Yiling Nie, Pengshan Xie, Xu Chen, Chenxing Jin, Wanrong Liu, Xiaofang Shi, Yunchao Xu, Yongyi Peng, Johnny C. Ho, Jia Sun, Junliang Yang
, Available online  

The emergence of light-tunable synaptic transistors provides opportunities to break through the Von Neumann bottleneck and enable neuromorphic computing. Herein, a multifunctional synaptic transistor is constructed by using 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and indium gallium arsenide (InGaAs) nanowires (NWs) hybrid heterojunction thin film as the active layer. Under illumination, the Type-I C8-BTBT/InGaAs NWs heterojunction would make the dissociated photogenerated excitons more difficult to recombine. The continuous photoconductivity caused by charge trapping can then be used to mimic photosynaptic behaviors, including excitatory postsynaptic current, long/short-term memory and Pavlovian learning. Furthermore, a high classification accuracy of 89.72% can be achieved through the single-layer-perceptron hardware-based neural network built from C8-BTBT/InGaAs NWs synaptic transistors. Thus, this work could provide new insights into the fabrication of high-performance optoelectronic synaptic devices.

The emergence of light-tunable synaptic transistors provides opportunities to break through the Von Neumann bottleneck and enable neuromorphic computing. Herein, a multifunctional synaptic transistor is constructed by using 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and indium gallium arsenide (InGaAs) nanowires (NWs) hybrid heterojunction thin film as the active layer. Under illumination, the Type-I C8-BTBT/InGaAs NWs heterojunction would make the dissociated photogenerated excitons more difficult to recombine. The continuous photoconductivity caused by charge trapping can then be used to mimic photosynaptic behaviors, including excitatory postsynaptic current, long/short-term memory and Pavlovian learning. Furthermore, a high classification accuracy of 89.72% can be achieved through the single-layer-perceptron hardware-based neural network built from C8-BTBT/InGaAs NWs synaptic transistors. Thus, this work could provide new insights into the fabrication of high-performance optoelectronic synaptic devices.
Synthesis and electromagnetic transport of large-area 2D WTe2 thin film
Yumeng Zhang, Zhejia Wang, Jiaheng Feng, Shuaiqiang Ming, Furong Qu, Yang Xia, Meng He, Zhimin Hu, Jing Wang
, Available online  
doi: 10.1088/1674-4926/43/10/102002

Tungsten telluride thin films were successfully prepared on monocrystal sapphire substrates by using atomic layer deposition and chemical vapor deposition technology, and the effects of different tellurization temperatures on the properties of tungsten telluride films were investigated. The growth rate, crystal structure and composition of the film samples were characterized and analyzed by using scanning electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that tungsten telluride thin films with good crystal orientation in (001) were obtained at telluride temperature of 550 °C. When the telluride temperature reached 570 °C, the tungsten telluride began to decompose and unsaturated magnetoresistance was found.

Tungsten telluride thin films were successfully prepared on monocrystal sapphire substrates by using atomic layer deposition and chemical vapor deposition technology, and the effects of different tellurization temperatures on the properties of tungsten telluride films were investigated. The growth rate, crystal structure and composition of the film samples were characterized and analyzed by using scanning electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that tungsten telluride thin films with good crystal orientation in (001) were obtained at telluride temperature of 550 °C. When the telluride temperature reached 570 °C, the tungsten telluride began to decompose and unsaturated magnetoresistance was found.
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.
Organic photodetectors with non-fullerene acceptors
Songxue Bai, Lixiu Zhang, Qianqian Lin, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/11/110201

Four-channel CWDM transmitter chip based on thin-film lithium niobate platform
Kaixuan Chen, Gengxin Chen, Ziliang Ruan, Xuancong Fan, Junwei Zhang, Ranfeng Gan, Jie Liu, Daoxin Dai, Changjian Guo, Liu Liu
, Available online  

Multi-lane integrated transmitter chips are key components in future compact optical modules to realize high-speed optical interconnects. Thin-film lithium niobate (TFLN) photonics have emerged as a promising platform for achieving high-performance chip-scale optical systems. Combining a coarse wavelength-division multiplexing (CWDM) devices using fabrication-tolerant angled multimode interferometer structure and high-performance electro-optical modulators, we demonstrate monolithic on-chip four-channel CWDM transmitter on the TFLN platform for the first time. The four-channel CWDM transmitter enables high-speed transmissions of 100 Gb/s data rate per wavelength channel (i.e., an aggregated date rate of 400 Gb/s).

Multi-lane integrated transmitter chips are key components in future compact optical modules to realize high-speed optical interconnects. Thin-film lithium niobate (TFLN) photonics have emerged as a promising platform for achieving high-performance chip-scale optical systems. Combining a coarse wavelength-division multiplexing (CWDM) devices using fabrication-tolerant angled multimode interferometer structure and high-performance electro-optical modulators, we demonstrate monolithic on-chip four-channel CWDM transmitter on the TFLN platform for the first time. The four-channel CWDM transmitter enables high-speed transmissions of 100 Gb/s data rate per wavelength channel (i.e., an aggregated date rate of 400 Gb/s).
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.
High photon detection efficiency InGaAs/InP single photon avalanche diode at 250 K
Tingting He, Xiaohong Yang, Yongsheng Tang, Rui Wang, Yijun Liu
, Available online  
doi: 10.1088/1674-4926/43/10/102301

Planar semiconductor InGaAs/InP single photon avalanche diodes with high responsivity and low dark count rate are preferred single photon detectors in near-infrared communication. However, even with well-designed structures and well-controlled operational conditions, the performance of InGaAs/InP SPADs is limited by the inherent characteristics of avalanche process and the growth quality of InGaAs/InP materials. It is difficult to ensure high detection efficiency while the dark count rate is controlled within a certain range at present. In this paper, we fabricated the device with a thick InGaAs absorption region and an anti-reflection layer. The quantum efficiency of device reaches 83.2%. We characterized the single-photon performance of the device by a quenching circuit consisting of parallel-balanced InGaAs/InP single photon detectors and single-period sinusoidal pulse gating. The spike pulse caused by the capacitance effect of the device is eliminated by using the characteristics of parallel balanced common mode signal elimination, and the detection of small avalanche pulse amplitude signal is realized. The maximum detection efficiency is 55.4% with a dark count rate of 43.8 kHz and an equivalent noise equivalent power of 6.96 × 10−19 W/Hz1/2 at 247 K. Compared with other reported detectors, this SPAD exhibits higher SPDE and lower noise-equivalent power at a higher cooling temperature.

Planar semiconductor InGaAs/InP single photon avalanche diodes with high responsivity and low dark count rate are preferred single photon detectors in near-infrared communication. However, even with well-designed structures and well-controlled operational conditions, the performance of InGaAs/InP SPADs is limited by the inherent characteristics of avalanche process and the growth quality of InGaAs/InP materials. It is difficult to ensure high detection efficiency while the dark count rate is controlled within a certain range at present. In this paper, we fabricated the device with a thick InGaAs absorption region and an anti-reflection layer. The quantum efficiency of device reaches 83.2%. We characterized the single-photon performance of the device by a quenching circuit consisting of parallel-balanced InGaAs/InP single photon detectors and single-period sinusoidal pulse gating. The spike pulse caused by the capacitance effect of the device is eliminated by using the characteristics of parallel balanced common mode signal elimination, and the detection of small avalanche pulse amplitude signal is realized. The maximum detection efficiency is 55.4% with a dark count rate of 43.8 kHz and an equivalent noise equivalent power of 6.96 × 10−19 W/Hz1/2 at 247 K. Compared with other reported detectors, this SPAD exhibits higher SPDE and lower noise-equivalent power at a higher cooling temperature.
Plasma atomic layer etching of GaN/AlGaN materials and application: An overview
Lulu Guan, Xingyu Li, Dongchen Che, Kaidong Xu, Shiwei Zhuang
, Available online  

With the development of the third generation of semiconductor devices, it is essential to achieve precise etching of gallium nitride (GaN) materials that is close to the atomic level. Compared with the traditional wet etching and continuous plasma etching, plasma atomic layer etching (ALE) of GaN has the advantages of self-limiting etching, high selectivity to other materials, and smooth etched surface. In this paper the basic properties and applications of GaN are presented. It also presents the various etching methods of GaN. GaN plasma ALE systems are reviewed, and their similarities and differences are compared. In addition, the industrial application of GaN plasma ALE is outlined.

With the development of the third generation of semiconductor devices, it is essential to achieve precise etching of gallium nitride (GaN) materials that is close to the atomic level. Compared with the traditional wet etching and continuous plasma etching, plasma atomic layer etching (ALE) of GaN has the advantages of self-limiting etching, high selectivity to other materials, and smooth etched surface. In this paper the basic properties and applications of GaN are presented. It also presents the various etching methods of GaN. GaN plasma ALE systems are reviewed, and their similarities and differences are compared. In addition, the industrial application of GaN plasma ALE is outlined.
Clarifying the atomic origin of electron killers in β-Ga2O3 from the first-principles study of electron capture rates
Zhaojun Suo, Linwang Wang, Shushen Li, Junwei Luo
, Available online  

The emerging wide bandgap semiconductor $ \beta $-Ga2O3 has attained great interest due to its promising applications for high-power electronic devices and solar-blind ultraviolet photodetectors. Deep-level defects in $ \beta $-Ga2O3 have been intensively studied towards improving device performance. Deep-level signatures E1, E2, and E3 with energy positions of 0.55–0.63, 0.74–0.81, and 1.01–1.10 eV below the conduction band minimum have been frequently observed and extensively investigated, but their atomic origins are still under debate. In this work, we attempt to clarify these deep-level signatures from the comparison of theoretically predicted electron capture cross-sections of suggested candidates, Ti and Fe substituting Ga on a tetrahedral site (TiGaI and FeGaI) and an octahedral site (TiGaII and FeGaII), to experimentally measured results. The first-principles approach predicted electron capture cross-sections of TiGaI and TiGaII defects are 8.56 × 10–14 and 2.97 × 10–13 cm2, in good agreement with the experimental values of E1 and E3, respectively. We, therefore, confirmed that E1 and E3 are indeed associated with TiGaI and TiGaII, respectively. Whereas the predicted electron capture cross-sections of FeGa defect are two orders of magnitude larger than the experimental value of the E2, which indicates E2 may have other origins like CGa, Gai, rather than FeGa.

The emerging wide bandgap semiconductor $ \beta $-Ga2O3 has attained great interest due to its promising applications for high-power electronic devices and solar-blind ultraviolet photodetectors. Deep-level defects in $ \beta $-Ga2O3 have been intensively studied towards improving device performance. Deep-level signatures E1, E2, and E3 with energy positions of 0.55–0.63, 0.74–0.81, and 1.01–1.10 eV below the conduction band minimum have been frequently observed and extensively investigated, but their atomic origins are still under debate. In this work, we attempt to clarify these deep-level signatures from the comparison of theoretically predicted electron capture cross-sections of suggested candidates, Ti and Fe substituting Ga on a tetrahedral site (TiGaI and FeGaI) and an octahedral site (TiGaII and FeGaII), to experimentally measured results. The first-principles approach predicted electron capture cross-sections of TiGaI and TiGaII defects are 8.56 × 10–14 and 2.97 × 10–13 cm2, in good agreement with the experimental values of E1 and E3, respectively. We, therefore, confirmed that E1 and E3 are indeed associated with TiGaI and TiGaII, respectively. Whereas the predicted electron capture cross-sections of FeGa defect are two orders of magnitude larger than the experimental value of the E2, which indicates E2 may have other origins like CGa, Gai, rather than FeGa.
Bulk GaN-based SAW resonators with high quality factors for wireless temperature sensor
Hongrui Lv, Xianglong Shi, Yujie Ai, Zhe Liu, Defeng Lin, Lifang Jia, Zhe Cheng, Jie Yang, Yun Zhang
, Available online  

Surface acoustic wave (SAW) resonator with outstanding quality factors of 4829/6775 at the resonant/anti-resonant frequencies has been demonstrated on C-doped semi-insulating bulk GaN. The impact of device parameters including aspect ratio of length to width of resonators, number of interdigital transducers, and acoustic propagation direction on resonator performance have been studied. For the first time, we demonstrate wireless temperature sensing from 21.6 to 120 °C with a stable temperature coefficient of frequency of –24.3 ppm/°C on bulk GaN-based SAW resonators.

Surface acoustic wave (SAW) resonator with outstanding quality factors of 4829/6775 at the resonant/anti-resonant frequencies has been demonstrated on C-doped semi-insulating bulk GaN. The impact of device parameters including aspect ratio of length to width of resonators, number of interdigital transducers, and acoustic propagation direction on resonator performance have been studied. For the first time, we demonstrate wireless temperature sensing from 21.6 to 120 °C with a stable temperature coefficient of frequency of –24.3 ppm/°C on bulk GaN-based SAW resonators.
Integration of high-performance spin-orbit torque MRAM devices by 200-mm-wafer manufacturing platform
Hongchao Zhang, Xiangyue Ma, Chuanpeng Jiang, Jialiang Yin, Shuqin Lyu, Shiyang Lu, Xiantao Shang, Bowen Man, Cong Zhang, Dandan Li, Shuhui Li, Wenjing Chen, Hongxi Liu, Gefei Wang, Kaihua Cao, Zhaohao Wang, Weisheng Zhao
, Available online  
doi: 10.1088/1674-4926/43/10/102501

We demonstrated in-plane field-free-switching spin-orbit torque (SOT) magnetic tunnel junction (MTJ) devices is capable of low switching current density, fast speed, high reliability, and, most importantly, manufactured uniformly by the 200-mm-wafer platform. The performances of the devices are systematically studied, including magnetic properties, switching behaviors, endurance and data retention of the devices. The successful integration of SOT devices within the 200-mm-wafer manufacturing platform provides a feasible way to industrialize SOT MRAMs. As a prospective, it is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.

We demonstrated in-plane field-free-switching spin-orbit torque (SOT) magnetic tunnel junction (MTJ) devices is capable of low switching current density, fast speed, high reliability, and, most importantly, manufactured uniformly by the 200-mm-wafer platform. The performances of the devices are systematically studied, including magnetic properties, switching behaviors, endurance and data retention of the devices. The successful integration of SOT devices within the 200-mm-wafer manufacturing platform provides a feasible way to industrialize SOT MRAMs. As a prospective, it is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.
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 of 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 of 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.
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.
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 2nd 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 2nd 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.
Organic electro-optic polymer materials and organic-based hybrid electro-optic modulators
Yan Wang, Tongtong Liu, Jiangyi Liu, Chuanbo Li, Zhuo Chen, Shuhui Bo
, Available online  
doi: 10.1088/1674-4926/43/10/101301

High performance electro-optic modulator, as the key device of integrated ultra-wideband optical system, has become the focus of research, and the organic-based hybrid electro-optic modulator, which makes full use of the advantages of organic electro-optic (OEO) materials, such as high electro-optic coefficient, fast response speed, high bandwidth, easy processing/integration and low cost, attracts a lot of attention. In this paper, we introduce a series of high-performance OEO materials which exhibit good properties in electro-optic activity and thermal stability. In addition, the recent progress of organic-based hybrid electro-optic devices including photonic crystal-organic hybrid (PCOH), silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) modulators are reviewed. The high-performance integrated optical platform based on OEO materials is a promising solution for growing high speeds and low power consumption in compact sizes request.

High performance electro-optic modulator, as the key device of integrated ultra-wideband optical system, has become the focus of research, and the organic-based hybrid electro-optic modulator, which makes full use of the advantages of organic electro-optic (OEO) materials, such as high electro-optic coefficient, fast response speed, high bandwidth, easy processing/integration and low cost, attracts a lot of attention. In this paper, we introduce a series of high-performance OEO materials which exhibit good properties in electro-optic activity and thermal stability. In addition, the recent progress of organic-based hybrid electro-optic devices including photonic crystal-organic hybrid (PCOH), silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) modulators are reviewed. The high-performance integrated optical platform based on OEO materials is a promising solution for growing high speeds and low power consumption in compact sizes request.
A review of thermal rectification in solid-state devices
Faraz Kaiser Malik, Kristel Fobelets
, Available online  
doi: 10.1088/1674-4926/43/10/103101

Thermal rectification, or the asymmetric transport of heat along a structure, has recently been investigated as a potential solution to the thermal management issues that accompany the miniaturization of electronic devices. Applications of this concept in thermal logic circuits analogous to existing electronics-based processor logic have also been proposed. This review highlights some of the techniques that have been recently investigated for their potential to induce asymmetric thermal conductivity in solid-state structures that are composed of materials of interest to the electronics industry. These rectification approaches are compared in terms of their quantitative performance, as well as the range of practical applications they would be best suited to. Techniques applicable to a range of length scales, from the continuum regime to quantum dots, are discussed, and where available, experimental findings that build upon numerical simulations or analytical predictions are also highlighted.

Thermal rectification, or the asymmetric transport of heat along a structure, has recently been investigated as a potential solution to the thermal management issues that accompany the miniaturization of electronic devices. Applications of this concept in thermal logic circuits analogous to existing electronics-based processor logic have also been proposed. This review highlights some of the techniques that have been recently investigated for their potential to induce asymmetric thermal conductivity in solid-state structures that are composed of materials of interest to the electronics industry. These rectification approaches are compared in terms of their quantitative performance, as well as the range of practical applications they would be best suited to. Techniques applicable to a range of length scales, from the continuum regime to quantum dots, are discussed, and where available, experimental findings that build upon numerical simulations or analytical predictions are also highlighted.
A deep trench super-junction LDMOS with double charge compensation layer
Lijuan Wu, Shaolian Su, Xing Chen, Jinsheng Zeng, Haifeng Wu
, Available online  
doi: 10.1088/1674-4926/43/10/104102

A deep trench super-junction LDMOS with double charge compensation layer (DC DT SJ LDMOS) is proposed in this paper. Due to the capacitance effect of the deep trench which is known as silicon–insulator–silicon (SIS) capacitance, the charge balance in the super-junction region of the conventional deep trench SJ LDMOS (Con. DT SJ LDMOS) device will be broken, resulting in breakdown voltage (BV) of the device drops. DC DT SJ LDMOS solves the SIS capacitance effect by adding a vertical variable doped charge compensation layer and a triangular charge compensation layer inside the Con. DT SJ LDMOS device. Therefor the drift region reaches an ideal charge balance state again. The electric field is optimized by double charge compensation and gate field plate so that the breakdown voltage of the proposed device is improved sharply, meanwhile the enlarged on-current region reduces its specific on-resistance. The simulation results show that compared with the Con. DT SJ LDMOS, the BV of the DC DT SJ LDMOS has been increased from 549.5 to 705.5 V, and the Ron,sp decreased to 23.7 mΩ·cm2.

A deep trench super-junction LDMOS with double charge compensation layer (DC DT SJ LDMOS) is proposed in this paper. Due to the capacitance effect of the deep trench which is known as silicon–insulator–silicon (SIS) capacitance, the charge balance in the super-junction region of the conventional deep trench SJ LDMOS (Con. DT SJ LDMOS) device will be broken, resulting in breakdown voltage (BV) of the device drops. DC DT SJ LDMOS solves the SIS capacitance effect by adding a vertical variable doped charge compensation layer and a triangular charge compensation layer inside the Con. DT SJ LDMOS device. Therefor the drift region reaches an ideal charge balance state again. The electric field is optimized by double charge compensation and gate field plate so that the breakdown voltage of the proposed device is improved sharply, meanwhile the enlarged on-current region reduces its specific on-resistance. The simulation results show that compared with the Con. DT SJ LDMOS, the BV of the DC DT SJ LDMOS has been increased from 549.5 to 705.5 V, and the Ron,sp decreased to 23.7 mΩ·cm2.
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.
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.
Multilayer doped-GeSe OTS selector for improved endurance and threshold voltage stability
Shiqing Zhang, Bing Song, Shujing Jia, Rongrong Cao, Sen Liu, Hui Xu, Qingjiang Li
, Available online  
doi: 10.1088/1674-4926/43/10/104101

Selector devices are indispensable components of large-scale memristor array systems. Thereinto, ovonic threshold switching (OTS) selector is one of the most suitable candidates for selector devices, owing to its high selectivity and scalability. However, OTS selectors suffer from poor endurance and stability which are persistent tricky problems for application. Here, we reported on a multilayer OTS selector based on simple GeSe and doped-GeSe. The experimental results showed improving selector performed extraordinary endurance up to 1010 and the fluctuation of threshold voltage is 2.5%. The reason for the improvement may lie in more interface states which strengthen the interaction among individual layers. These developments pave the way towards tuning a new class of OTS materials engineering, ensuring improvement of electrical performances.

Selector devices are indispensable components of large-scale memristor array systems. Thereinto, ovonic threshold switching (OTS) selector is one of the most suitable candidates for selector devices, owing to its high selectivity and scalability. However, OTS selectors suffer from poor endurance and stability which are persistent tricky problems for application. Here, we reported on a multilayer OTS selector based on simple GeSe and doped-GeSe. The experimental results showed improving selector performed extraordinary endurance up to 1010 and the fluctuation of threshold voltage is 2.5%. The reason for the improvement may lie in more interface states which strengthen the interaction among individual layers. These developments pave the way towards tuning a new class of OTS materials engineering, ensuring improvement of electrical performances.
Hyperdoped silicon: Processing, properties, and devices
Zhouyu Tong, Mingxuan Bu, Yiqiang Zhang, Deren Yang, Xiaodong Pi
, Available online  
doi: 10.1088/1674-4926/43/9/093101

Hyperdoping that introduces impurities with concentrations exceeding their equilibrium solubility has been attracting great interest since the tuning of semiconductor properties increasingly relies on extreme measures. In this review we focus on hyperdoped silicon (Si) by introducing methods used for the hyperdoping of Si such as ion implantation and laser doping, discussing the electrical and optical properties of hyperdoped bulk Si, Si nanocrystals, Si nanowires and Si films, and presenting the use of hyperdoped Si for devices like infrared photodetectors and solar cells. The perspectives of the development of hyperdoped Si are also provided.

Hyperdoping that introduces impurities with concentrations exceeding their equilibrium solubility has been attracting great interest since the tuning of semiconductor properties increasingly relies on extreme measures. In this review we focus on hyperdoped silicon (Si) by introducing methods used for the hyperdoping of Si such as ion implantation and laser doping, discussing the electrical and optical properties of hyperdoped bulk Si, Si nanocrystals, Si nanowires and Si films, and presenting the use of hyperdoped Si for devices like infrared photodetectors and solar cells. The perspectives of the development of hyperdoped Si are also provided.
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.
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.
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

Perovskite nanocrystals for light-emitting diodes
Xinyi Mei, Lixiu Zhang, Xiaoliang Zhang, Liming Ding
, Available online  
doi: 10.1088/1674-4926/43/9/090201

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.