High-performance 4H-SiC p-i-n ultraviolet avalanche photodiodes with large active area

Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area(800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process,a high multiplication gain of 1.4 × 10~6 is obtained for the devices at room temperature, and the dark current is as low as ～10 p A at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported Si C APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10~4. The excellent performance of our devices indicates a tremendous improvement for largearea SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4 H-SiC p-i-n APDs is also demonstrated for system-level applications.     

Transient simulation and analysis of current collapse due to trapping effects in AlGaN/GaN high-electron-mobility transistor

In this paper, two-dimensional(2D) transient simulations of an Al Ga N/Ga N high-electron-mobility transistor(HEMT)are carried out and analyzed to investigate the current collapse due to trapping effects. The coupling effect of the trapping and thermal effects are taken into account in our simulation. The turn-on pulse gate-lag transient responses with different quiescent biases are obtained, and the pulsed current–voltage(I–V) curves are extracted from the transients. The experimental results of both gate-lag transient current and pulsed I–V curves are reproduced by the simulation, and the current collapse due to the trapping effect is explained from the view of physics based on the simulation results. In addition, the results show that bulk acceptor traps can influence the gate-lag transient characteristics of Al Ga N/Ga N HEMTs besides surface traps and that the thermal effect can accelerate the emission of captured electrons for traps. Pulse transient simulation is meaningful in analyzing the mechanism of dynamic current collapse, and the work in this paper will benefit the reliability study and model development of Ga N-based devices.     

Large-area 4H-SiC avalanche photodiodes with high gain and low dark current for visible-blind ultraviolet detection

In this Letter, we report large-area(600 μm diameter) 4H-SiC avalanche photodiodes(APDs) with high gain and low dark current for visible-blind ultraviolet detection. Based on the separate absorption and multiplication structure, 4H-SiC APDs passivated with SiN_xinstead of SiO_2 are demonstrated for the first time, to the best of our knowledge. Benefitting from the SiN_x passivation, the surface leakage current is effectively suppressed. At room temperature, high multiplication gain of 6.5 × 10~5 and low dark current density of 0.88 μA∕cm~2 at the gain of 1000 are achieved for our devices, which are comparable to the previously reported small-area Si C APDs.     

A unified charge-based model for SOI MOSFETs applicable from intrinsic to heavily doped channel

A unified charge-based model for fully depleted silicon-on-insulator (SOI) metal–oxide semiconductor field-effect transistors (MOSFETs) is presented. The proposed model is accurate and applicable from intrinsic to heavily doped channels with various structure parameters. The framework starts from the one-dimensional Poisson–Boltzmann equa- tion, and based on the full depletion approximation, an accurate inversion charge density equation is obtained. With the inversion charge density solution, the unified drain current expression is derived, and a unified terminal charge and intrinsic capacitance model is also derived in the quasi-static case. The validity and accuracy of the presented analytic model is proved by numerical simulations.     

A continuous analytic channel potential solution to doped symmetric double-gate MOSFETs from the accumulation to the strong-inversion region

A continuous yet analytic channel potential solution is proposed for doped symmetric double-gate (DG) MOSFETs from the accumulation to the strong-inversion region. Analytical channel potential relationship is derived from the complete 1-D Poisson equation physically, and the channel potential solution of the DG MOSFET is obtained analytically. The extensive comparisons between the presented solution and the numerical simulation illustrate that the solution is not only accurate and continuous in the whole operation regime of DG MOSFETs, but also valid to wide doping concentration and various geometrical sizes, without employing any fitting parameter.     

An improvement to computational efficiency of the drain current model for double-gate MOSFET

As a connection between the process and the circuit design, the device model is greatly desired for emerging devices, such as the double-gate MOSFET. Time efficiency is one of the most important requirements for device modeling. In this paper, an improvement to the computational efficiency of the drain current model for double-gate MOSFETs is extended, and different calculation methods are compared and discussed. The results show that the calculation speed of the improved model is substantially enhanced. A two-dimensional device simulation is performed to verify the improved model. Furthermore, the model is implemented into the HSPICE circuit simulator in Verilog-A for practical application.     

基于脉冲方法的超短栅长GaN基高电子迁移率晶体管陷阱效应机理

陷阱效应导致的电流崩塌是制约GaN基微波功率电子器件性能提高的一个重要因素,研究深能级陷阱行为对材料生长和器件开发具有非常重要的意义.随着器件频率的提升,器件尺寸不断缩小,对小尺寸器件中深能级陷阱的表征变得越发困难.本文制备了超短栅长（L_g=80 nm）的AlGaN/GaN金属氧化物半导体高电子迁移率晶体管（MOSHEMT）,并基于脉冲I-V测试和二维数值瞬态仿真对器件的动态特性进行了深入研究,分析了深能级陷阱对AlGaN/GaN MOSHEMT器件动态特性的影响以及相关陷阱效应的内在物理机制.结果表明,AlGaN/GaN MOSHEMT器件的电流崩塌随着栅极静态偏置电压的增加呈非单调变化趋势,这是由栅漏电注入和热电子注入两种陷阱机制共同作用的结果.根据研究结果推断,可通过改善栅介质的质量以减小栅漏电或提高外延材料质量以减少缺陷密度等措施达到抑制陷阱效应的目的,从而进一步抑制电流崩塌.     

Performance analysis of GaN-based high-electron-mobility transistors with postpassivation plasma treatment

AlGaN/GaN high-electron-mobility transistors(HEMTs)with postpassivation plasma treatment are demonstrated and investigated for the first time.The results show that postpassivation plasma treatment can reduce the gate leakage and enhance the drain current.Comparing with the conventional devices,the gate leakage of Al Ga N/Ga N HEMTs with postpassivation plasma decreases greatly while the drain current increases.Capacitance-voltage measurement and frequencydependent conductance method are used to study the surface and interface traps.The mechanism analysis indicates that the surface traps in the access region can be reduced by postpassivation plasma treatment and thus suppress the effect of virtual gate,which can explain the improvement of DC characteristics of devices.Moreover,the density and time constant of interface traps under the gate are extracted and analyzed.