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.

Mechanisms of trapping effects in short-gate GaN-based high electron mobility transistors with pulsed I-V measurement

Deep-level trapping effect is one of the most critical issues that restrict the performance improvement of GaN-based microwave power devices. It is of very importance for material growth and device development to study the trapping behavior in the device. In the past decades, there have been made a lot of efforts to characterize and investigate the deep-level trapping phenomena. However, most of the previous researches focused on the large-scale devices. For pursuing higher frequency, the devices need to be scaled down. Consequently, it becomes more difficult to characterize the deep-level traps in small-scale GaN-based devices, since none of the traditional characterization techniques such as capacitance-voltage (C-V) measurement and capacitance deep-level transient spectroscopy (C-DLTS) are applicable to small devices. Pulsed I-V measurement and transient simulation are useful techniques for analyzing trapping effects in AlGaN/GaN high electron mobility transitors (HEMTs). In this work, AlGaN/GaN metal-oxide-semiconductor HEMTs (MOSHEMTs) with very short gate length (L_g=80 nm) are fabricated. Based on the pulsed I-V measurement and two-dimensional transient simulation, the influence of deep-level trap on the dynamic characteristic of short-gate AlGaN/GaN MOSHEMT is investigated. First, the pulsed I-V characteristics of AlGaN/GaN MOSHEMT with different quiescent bias voltages are studied. In addition, the current collapse induced by the trapping effect is extracted as a function of the quiescent bias voltage. Furthermore, the transient current of AlGaN/GaN MOSHEMT is simulated with the calibrated model, and the simulation exhibits a similar result to the measurement. Moreover, the physical mechanism of trapping effect in the device is analyzed based on the experimental data and simulation results. It is shown that the current collapse of AlGaN/GaN MOSHEMT varies non-monotonically with the increase of the gate quiescent bias voltage, which results from the combination effect of the gate leakage injection-related and hot electron injection-related mechanism. In the off state, the current collapse is mainly induced by the traps below the gate, which is dominated by the gate leakage injection mechanism, leading to the decrease of current collapse with the increase of the gate bias voltage. In the on state, the hot electron injection mechanism becomes the dominant factor for trapping effect in the drain access region, resulting in the increase of current collapse. The results in this work indicate that the trap-induced current collapse can be further suppressed by improving the quality of gate dielectric to minimize the gate reverse leakage and by reducing the trap density in the epitaxial layer.