Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18Al0.82N/AIN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.     

玻璃-陶瓷脉冲形成线的充放电特性

采用熔融-快冷-可控结晶工艺，制备了(Pb，Sr)Nb₂O₆-NaNbO₃-SiO₂大尺寸玻璃陶瓷，开展了其介电性能以及脉冲充放电特性研究。实验结果表明:该玻璃陶瓷材料的介电常数约为340，具有良好的温度稳定性和正的偏压特性。基于该材料制备的固态脉冲形成线输出脉冲脉宽约为89 ns，具有良好的脉冲平顶和窄的上升沿。在19 kV充放电电压、1 kHz的充放电频率、4 kA的放电电流条件下，固态脉冲形成线充放电寿命大于100万次。     

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18 Al0.82 N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional(quasi-2D) model, the current–voltage(I–V) characteristics of In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors(HFETs) with different gate lengths are simulated based on the measured capacitance–voltage(C–V) characteristics and I–V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas(2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V·s for the prepared In0.18Al0.82N/AlN/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain–source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density,the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.     

Electron mobility in the linear region of an AlGaN/AlN/GaN heterostructure field-effect transistor

We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas （213EG） with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.     

Influence of drain bias on the electron mobility in AlGaN/AlN/GaN heterostructure field-effect transistors

Using measured capacitance-voltage curves and current-voltage characteristics for the AlGaN/AlN/GaN heterostructure field-effect transistors with different gate lengths and drain-to-source distances,the influence of drain bias on the electron mobility is investigated.It is found that below the knee voltage the longitudinal optical(LO) phonon scattering and interface roughness scattering are dominant for the sample with a large ratio of gate length to drain-to-source distance(here 4/5),and the polarization Coulomb field scattering is dominant for the sample with a small ratio(here 1/5).However,the above polarization Coulomb field scattering is weakened in the sample with a small drain-to-source distance(here 20 μm) compared with the one with a large distance(here 100 μm).This is due to the induced strain in the AlGaN layer caused by the drain bias.     

Different influences of Schottky metal on the strain and relative permittivity of barrier layer between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated.Based on the measured current–voltage and capacitance-voltage curves,the polarization sheet charge density and relative permittivity are analyzed and calculated by self-consistently solving Schrdinger’s and Poisson’s equations.It is found that the values of relative permittivity and polarization sheet charge density of AlN/GaN diode are both much smaller than the ones of AlGaN/GaN diode,and also much lower than the theoretical values.Moreover,by fitting the measured forward I–V curves,the extracted dislocations existing in the barrier layer of the AlN/GaN diode are found to be much more than those of the AlGaN/GaN diode.As a result,the conclusion can be made that compared with AlGaN/GaN diode the Schottky metal has an enhanced influence on the strain of the extremely thinner AlN barrier layer,which is attributed to the more dislocations.     

Influence of thermal stress on the characteristic parameters of AlGaN/GaN heterostructure Schottky contacts

Ni Schottky contacts on AlGaN/GaN heterostructures have been fabricated. The samples are then thermally treated in a furnace with N₂ ambient at 600 ^circC for different times (0.5, 4.5, 10.5, 18, 33, 48 and 72 h). Current-voltage (I-V) and capacitance-voltage (C-V) relationships are measured, and Schrödinger's and Poisson's equations are self-consistently solved to obtain the characteristic parameters related to AlGaN/GaN heterostructure Schottky contacts: the two-dimensional electron gas (2DEG) sheet density, the polarization sheet charge density, the 2DEG distribution in the triangle quantum well and the Schottky barrier height for each thermal stressing time. Most of the above parameters reduce with the increase of stressing time, only the parameter of the average distance of the 2DEG from the AlGaN/GaN interface increases with the increase of thermal stressing time. The changes of the characteristic parameters can be divided into two stages. In the first stage the strain in the AlGaN barrier layer is present. In this stage the characteristic parameters change rapidly compared with those in the second stage in which the AlGaN barrier layer is relaxed and no strain is present.     

Different influences of Schottky metal on the strain and relative permittivity of barrier layer between AIN/GaN and AIGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated. Based on the measured current-voltage and capacitance-voltage curves, the polarization sheet charge density and relative permittivity are analyzed and calculated by self-consistently solving Schrodinger＇s and Poisson＇s equations. It is found that the values of relative permittivity and polarization sheet charge density of AlN/GaN diode are both much smaller than the ones of AlGaN/GaN diode, and also much lower than the theoretical values. Moreover, by fitting the measured forward 1-V curves, the extracted dislocations existing in the barrier layer of the AlN/GaN diode are found to be much more than those of the AlGaN/GaN diode. As a result, the conclusion can be made that compared with AlGaN/GaN diode the Schottky metal has an enhanced influence on the strain of the extremely thinner AlN barrier layer, which is attributed to the more dislocations.     

Determination of the series resistance under the Schottky contacts of AlGaN/AlN/GaN Schottky barrier diodes

Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) were fabricated,and the gate and the source of the HFETs consisted of AlGaN/AlN/GaN Schottky barrier diodes (SBDs).Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs,the series resistance under the Schottky contacts (RS) was calculated using the method of power consumption,which has been proved to be valid.Finally,the method of power consumption for calculating R S was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs.It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AlGaN/AlN/GaN SBDs and the AlGaN/AlN/GaN HFETs.     

模块化多路同步快脉冲触发源设计

基于超快速高压大功率半导体开关、脉冲形成电路以及同心等间距传输的关键技术,提出一种模块化多路同步快脉冲触发源技术方案。设计出在负载阻抗为50Ω时,可同步输出两种快脉冲触发信号:一种幅度大于20V(4路)、脉冲前沿小于820ps、脉冲宽度大于100ns;另一种则是幅度大于100V(4路)、前沿小于1.4ns、脉宽大于100ns;在外触发作用下,触发源系统抖动和脉冲输出同步分散性分别达到2ns和36.6ps。电路结构上充分利用等间距电信号传输的原理,实现了快脉冲触发源模块化的设计。通过实验结果验证了所采用的设计原理及方法的可行性,给出了在外触发脉冲单次和重频(5kHz)作用下该同步快脉冲触发源输出的实验结果。