空穴气增强型高压GaN HEMT机理与新结构研究

In view of the key issues of enhancement mode (E-mode), breakdown voltage (BV) and leakage current in GaN power electronics devices, the following innovative researches will be implemented: 1. Mechanism and Novel structure of Hole Gas Enhancement-mode High-Voltage GaN HEMT is proposed. The GaN/AlGaN/GaN dual-heterojunction and a vertical channel are designed. The 2DHG and 2DEG are introduced in the dual-heterojunction, and the polarization junction is formed by 2DHG and 2DEG. The Novel Mechanisms of the proposed include: ①2DHG blocks the vertical channel to realize the E-mode. The proposed HEMT maintains high threshold voltage and large output current; ②The BV is improved by polarization junction and the source field plate. Polarization junction has the assisted depletion effect on the drift region and modulates the electric field distribution in the drift region; The source and drain locate at the same side of the gate and the source act as a field plate, improving the BV and decreasing the device size; ③The MIS recessed gate is used to suppress the leakage current and increase the gate voltage swing. The threshold voltage of 1.5V-3V for the novel HEMT is designed and output current is more than 400mA/mm. Compared with conventional HEMT, the proposed HEMT increases the BV by more than 30%. 2. The charge-controlled model for threshold voltage is presented. Based on the polarization theory and the energy band engineering, the energy band structure is changed by modulating the 2DHG concentration, and thus the threshold voltage is controlled. 3. The proposed GaN HEMT is to be fabricated. The device failure mechanism will be studied and the leakage-suppressed technology is explored. This project has frontier innovative significance and practical value.

针对GaN电力电子器件中增强型、耐压、漏电等关键问题，进行以下创新研究：1.提出空穴气增强型高压GaN HEMT机理与新结构。构建GaN/AlGaN /GaN双异质结和纵向沟道结构，形成由2DHG和2DEG构成的极化结。机理含①空穴气阻断纵向沟道实现增强型，器件兼具高阈值电压和高输出电流。②极化结和源极场板提高器件耐压。极化结辅助耗尽漂移区并调制电场分布；源、漏极位于栅极同侧并构成源场板，提高耐压且缩小器件尺寸。③MIS凹槽栅抑制泄漏电流并增大栅压摆幅。新器件阈值电压达1.5-3.0V，输出电流大于400mA/mm，耐压较相同尺寸的常规GaN HEMT提高30%以上。2.建立阈值电压电荷控制模型。基于极化理论和能带工程，通过调制2DHG浓度而改变异质结能带结构，实现对阈值电压控制。3.研制所提GaN HEMT，分析失效机制，探索漏电抑制技术。本项目研究具有前沿基础创新性和实用价值。

GaN材料具有宽禁带、高电子饱和速度及高临界击穿电场等特点，加上GaN异质结具有高浓度二维电子气（2DEG），使得GaN功率器件在高压、大功率及低功耗方面独具优势。针对如何实现增强型、高耐压和高可靠性等关键问题，对高质量栅介质生长、低阻欧姆接触、低损伤刻蚀以及界面处理等关键工艺进行攻关，提出并研制2类新型高压低功耗GaN器件样品。第一类提出具有空穴气的高压GaN器件机理与新结构，构建GaN/AlGaN/GaN双异质结和纵向沟道结构，由2DHG和2DEG构成的极化结优化漂移区电场，实现高压；HEMT还利用二维空穴气（2DHG）阻断源极二维电子气（2DEG）的纵向沟道，实现增强型；开发了速度可控及低损伤的ICP刻蚀技术，降低界面、抑制泄漏电流，开发厚AlGaN外延层低阻欧姆制备技术；研制具有空穴气的肖特基二极管，器件的开启电压为0.68V，器件耐压达1109V，比导通电阻为1.17mΩ·cm2，开关电流比~10e10。第二类具有新型终端技术的增强型GaN HEMT器件，新型终端优化漂移区电场分布，提高耐压。包括：具有钝化层氟离子注入终端的HEMT，击穿电压为803V，氟离子注入钝化层抑制了电流崩塌，提高了可靠性，当应力电压为100V时，器件的动态导通电阻仅增大了23%；研制出具有新型槽终端结构的GaN HEMT，击穿电压为412V，导通电阻为7.42Ω·mm，饱和输出电流为505mA/mm，阈值电压为1.33V，刻蚀界面陷阱浓度下降了近一个数量级。基于极化理论和能带工程，建立阈值电压电荷控制模型，实现对阈值电压有效控制。以该项目研究成果为主要支撑内容发表论文10篇，获授权美国专利1项、授权中国发明专利4项，已受理中国发明专利申请11项，达到项目指标。