Recessed-gate quasi-enhancement-mode AlGaN/GaN high electron mobility transistors with oxygen plasma treatment

In this paper,the enhancement-mode AlGaN/GaN HEMT combined with the low damage recessed-gate etching and the optimized oxygen plasma treatment was fabricated.Scanning electron microscope/energy dispersive spectrometer(SEM/EDS) method and x-ray photoelectron spectroscopy(XPS) method were used to confirm the formation of oxides.Based on the experimental results,the obtained enhancement-mode HEMT exhibited a threshold voltage of 0.5 V,a high peak transconductance of 210 mS/mm,and a maximum drain current of 610 mA/mm at the gate bias of 4 V.Meanwhile,the on/off current ratio of enhancement-mode HEMT was as high as 10~8,drain induced barrier lowering(DIBL) was as low as 5 raV/V,and subthreshold swing(SS) of 80 mV/decade was obtained.Compared with the conventional HEMT,the Schottky reverse current of enhancement-mode HEMT was three orders of magnitude lower,and the off-state breakdown voltage of which was higher.In addition,a power gain cutoff frequency(/max) of the enhancement-mode HEMT was larger than that of the conventional one.     

Analysis of the modulation mechanisms of the electric field and breakdown performance in AlGaN/GaN HEMT with a T-shaped field-plate

A novel Al Ga N/Ga N high electron mobility transistor(HEMT) with a source-connected T-shaped field-plate(ST-FP HEMT) is proposed for the first time in this paper. The source-connected T-shaped field-plate(ST-FP) is composed of a source-connected field-plate(S-FP) and a trench metal. The physical intrinsic mechanisms of the ST-FP to improve the breakdown voltage and the FP efficiency and to modulate the distributions of channel electric field and potential are studied in detail by means of two-dimensional numerical simulations with Silvaco-ATLAS. A comparison to the HEMT and the HEMT with an S-FP(S-FP HEMT) shows that the ST-FP HEMT could achieve a broader and more uniform channel electric field distribution with the help of a trench metal, which could increase the breakdown voltage and the FP efficiency remarkably. In addition, the relationship between the structure of the ST-FP, the channel electric field, the breakdown voltage as well as the FP efficiency in ST-FP HEMT is analyzed. These results could open up a new effective method to fabricate high voltage power devices for the power electronic applications.     

Improvement of reverse blocking performance in vertical power MOSFETs with Schottky–drain-connected semisuperjunctions

To enhance the reverse blocking capability with low specific on-resistance,a novel vertical metal-oxidesemiconductor field-effect transistor(MOSFET) with a Schottky-drian(SD) and SD-connected semisuperjunctions(SDD-semi-SJ),named as SD-D-semi-SJ MOSFET is proposed and demonstrated by two-dimensional(2D) numerical simulations.The SD contacted with the n-pillar exhibits the Schottky-contact property,and that with the p-pillar the Ohmic-contact property.Based on these features,the SD-D-semi-SJ MOSFET could obviously overcome the great obstacle of the ineffectivity of the conventional superjunctions(SJ) or semisuperjunctions(semi-SJ) for the reverse applications and achieve a satisfactory trade-off between the reverse breakdown voltage(BV) and the specific on-resistance(R_(on)A).For a given pillar width and n-drift thickness,there exists a proper range of n-drift concentration(N),in which the SD-D-semi-SJ MOSFET could exhibit a better trade-off of R_(on)A-BV compared to the predication of SJ MOSFET in the forward applications.And what is much valuable,in this proper range of N,the desired BV and good trade-off could be achieved only by determining the pillar thickness,with the top assist layer thickness unchanged.Detailed analyses have been carried out to get physical insights into the intrinsic mechanism of R_(on)A-BV improvement in SD-D-semi-SJ MOSFET.These results demonstrate a great potential of SD-D-semi-SJ MOSFET in reverse applications.     

Characterization of Al2O3 /GaN/AlGaN/GaN metalinsulator-semiconductor high electron mobility transistors with different gate recess depths

In this paper,in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs),we demonstrate better performances of recessed-gate Al 2 O 3 MIS-HEMTs which are fabricated by Fluorine-based Si 3 N 4 etching and chlorinebased AlGaN etching with three etching times (15 s,17 s and 19 s).The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT.Through the recessed-gate etching,the transconductance increases effectively.When the recessed-gate depth is 1.02 nm,the best interface performance with τ it =(0.20-1.59) μs and D it =(0.55-1.08)×10 12 cm 2 ·eV 1 can be obtained.After chlorine-based etching,the interface trap density reduces considerably without generating any new type of trap.The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices.By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times,it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively.     

不同晶面的氢终端单晶金刚石场效应晶体管特性

通过微波等离子体化学气相淀积技术生长单晶金刚石并切割得到(110)和(111)晶面金刚石片,以同批器件工艺制备两种晶面上栅长为6μm的氢终端单晶金刚石场效应管,从材料和器件特性两方面对两种晶面金刚石进行对比分析.(110)面和(111)面金刚石的表面形貌在氢终端处理后显著不同,光学性质则彼此相似.VGS=–4 V时,(111)金刚石器件获得的最大饱和电流为80.41 m A/mm,约为(110)金刚石器件的1.4倍;其导通电阻为48.51 W·mm,只有(110)金刚石器件导通电阻的67%.通过对器件电容-电压特性曲线的分析得到,(111)金刚石器件沟道中最大载流子密度与(110)金刚石器件差异不大.分析认为,(111)金刚石器件获得更高饱和电流和更低导通电阻,应归因于较低的方阻.     

爆炸冲击作用时间差对盆骨和腰椎的损伤研究

为研究爆炸冲击环境下车内乘员小腿和座椅所受垂向冲击时间差对乘员盆骨和腰椎损伤的影响,利用Hyperworks和LS-DYNA进行建模和仿真分析,并结合小腿冲击试验和座椅跌落试验开展研究。分析结果表明:乘员小腿和座椅安装点单独受冲击时盆骨加速度、动态响应指数和腰椎z向力会分别产生正向和负向的峰值,但同时作用并控制冲击时间间隔时并不会出现正负峰值相抵消的现象;小腿和座椅安装点不同时受冲击时会加重乘员盆骨和腰椎损伤,且小腿先受冲击时损伤程度较座椅安装点先受冲击时严重。     

垂向冲击下穿戴装备对乘员损伤影响研究

军事人员在战斗中需要穿戴装备,穿戴装备后对车内乘员承受车辆底部爆炸垂向冲击时的损伤有影响。通过垂向冲击试验与仿真模拟的方法,研究了穿戴装备在身上的分布对于乘员损伤的影响。根据AEP55乘员伤害准则,以盆骨z向加速度和腰椎轴向力为乘员损伤的参考目标,首先通过垂向冲击试验的进行,研究了不同穿戴装备质量对于乘员损伤的影响;接着通过有限元模型对试验进行验证和优化,进而研究穿戴装备位置与松紧度对于垂向冲击下乘员损伤的影响。结果表明随着穿戴装备质量的增加,乘员腰椎损伤加重,脊柱损伤概率减小;装备分布在躯干位置越靠近上部,与身体接触松紧度越紧,乘员腰椎与脊柱的负荷越小,越不易受伤。     

Improved mobility of AIGaN channel heterojunction material using an AIGaN/GaN composite buffer layer

The quality of an A1GaN channel heterojunction on a sapphire substrate is massively improved by using an A1- GaN/GaN composite buffer layer. We demonstrate an A10.4Gao.6N/AI0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/（V.s） and a sheet resistance of 890Ω/口 under room temperature. The crystalline quality and the electrical properties of the A1GaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance-voltage （C-V） measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.     

AlGaN/GaN high-electron-mobility transistors with transparent gates by Al-doped ZnO

AlGaN/GaN high-electron-mobility transistors （HEMTs） with Al-doped ZnO （AZO） transparent gate electrodes are fabricated, and Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show a low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMTs exhibit a current-gain cutoff frequency （fT） of 10 GHz and a power gain cutoff frequency （fmax） of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the C-V characteristics are measured and the gate interface characteristics of the AZO-gated devices are investigated by a C-V dual sweep.