Fabrication and Characterization of High-Breakdown and High-Power GaN HEMTs

为了实现高击穿、大功率GaN HEMT器件，我们对GaN HEMT器件的制备和特性进行了研究。主要结果如下：1.已经阐明，关态击穿电压由从栅电极注入的电子主导。采用Si_3N_4栅绝缘层可以降低影响击穿电压的栅漏电流. GaN MISHEMT的关态击穿电压从传统GaN HEMT的70-80 V提高到160-200 V。电流崩塌是传统GaN HEMT输出功率下降的主要因素之一，MISHEMT的电流崩塌得到了抑制.结果表明，漏极电流DLTS是研究GaN HEMT瞬态特性的有效方法。它也已被澄清，使用这种技术，起源于表面态的正峰已被抑制在MISHEMT中。采用高介电常数的HfO_2作为栅绝缘层，解决了Si_3N_4 MISHEMT的栅电阻小的问题.斜栅凹槽结构被提出来改善HEMT的高速性能。它已被证明，所提出的结构是有效的，在提高器件性能的基础上的器件模拟和器件制造。

We have studied the fabrication and characterization of GaN HEMT to realize the high-breakdown and high-power GaN HEMTs. The main results we have obtained are as follows.1. It has been clarified that the off-state breakdown voltage is dominated by the electrons injected from the gate electrode.2. The gate leakage current which affects the breakdown voltage could be decreased in the GaN MISHEMTs with Si_3N_4 gate insulator.3. The off-state breakdown voltage of the GaN MISHEMTs has been increased from 70-80 V of the conventional GaN HEMTs to 160-200 V.4. The current collapse which is one of the dominant factors to decrease the output power of the conventional GaN HEMTs was suppressed in the MISHEMTs.5. It has been demonstrated that the drain current DLTS is effective in studying the transient behavior of the GaN HEMTs. It has also been clarified, using this technique, that the positive peak originating the surface states has been suppressed in the MISHEMTs.6. The issue of small transconductance of the Si_3N_4 MISHEMTs has been solved by using HfO_2 with high dielectric constant as a gate insulator.7. The inclined gate recess structure has been proposed to improve the high-speed performance of the HEMTs. It has been shown that the proposed structure is effective in improving the device performance based on the device simulation and on the device fabrication.