阶梯AlGaN外延新型Al_(0.25)Ga_(0.75)N/GaNHEMTs击穿特性分析

为了优化AlGaN/GaN HEMTs器件表面电场,提高击穿电压,本文首次提出了一种新型阶梯AlGaN/GaN HEMTs结构.新结构利用AlGaN/GaN异质结形成的2DEG浓度随外延AlGaN层厚度降低而减小的规律,通过减薄靠近栅边缘外延的AlGaN层,使沟道2DEG浓度分区,形成栅边缘低浓度2DEG区,低的2DEG使阶梯AlGaN交界出现新的电场峰,新电场峰的出现有效降低了栅边缘的高峰电场,优化了AlGaN/GaN HEMTs器件的表面电场分布,使器件击穿电压从传统结构的446 V,提高到新结构的640 V.为了获得与实际测试结果一致的击穿曲线,本文在GaN缓冲层中设定了一定浓度的受主型缺陷,通过仿真分析验证了国际上外延GaN缓冲层时掺入受主型离子的原因,并通过仿真分析获得了与实际测试结果一致的击穿曲线.

Breakdown voltage analysis for the new Al0.25 Ga0.75N/GaN HEMTs with the step AlGaN layers

In order to optimize the surface electric field of AlGaN/GaN high electron mobility transistors (HEMTs), a novel AlGaN/GaN HEMT has been grown with a step AlGaN layer, made for the first time as far as we know, to improve the breakdown voltage. The discipline of the 2DEG concentration varying with the thickness of the AlGaN epitaxy layer has been applied to the new AlGaN/GaN HEMTs with AlGaN/GaN heterostructure. By thinning the AlGaN layer near the gate edge, the 2DEG concentration in the channel is made to form the low concentration region near the gate edge. New electric field peak has appeared at the corner of the step AlGaN layer. The high electric field has been decreased effectively due to the emergence of new electric field peak; this optimizes the surface electric field of the new AlGaN/GaN HEMTs. Then the breakdown voltage is improved to 640 V in the new AlGaN/GaN HEMTs with the step AlGaN layer as compared with 446 V for the conventional structure. In order to let the breakdown curve consistent with the test results, a certain concentration of the acceptor-like traps is added to the GaN buffer to capture the leaking current coming from the source electrode. Simulation results verify the causes for doping acceptor type ions to the GaN buffer, given by foreign researchers. The breakdown curves have been obtained which are consistent with the test results in this paper.
Keywords： AlGaN/GaN surface electric field breakdown voltage heterojunction