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

为了实现高击穿、高功率的GaN HEMT，我们研究了GaN HEMT的制备和表征。我们所取得的主要结果如下：1.已经阐明了关态击穿电压是由从栅极注入的电子主导的。采用Si_3N_4栅绝缘层可以降低GaN MISHEMTs中影响击穿电压的栅漏电流。GaN MISHEMTs的关态击穿电压已从传统GaN HEMT的70-80V提高到160-200V。电流崩塌是导致传统GaN HEMT输出功率降低的主要因素之一，在MISHEMT中得到了抑制。结果表明，漏电流DLTS对于研究GaN HEMT的暂态行为是有效的。使用这项技术还澄清了，在MISHEMT中，产生表面态的正峰已经被抑制。用高介电常数的HfO_2作栅绝缘体，解决了Si_3N_4异质结跨导小的问题。为提高HEMTs的高速性能，提出了斜栅凹槽结构。基于器件模拟和器件制作的结果表明，该结构在改善器件性能方面是有效的。

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.