基于“背栅同步高压脉冲深能级瞬态谱”的氮化镓电流崩塌机理研究

With excellent breakdown resistance, low conduction, and high frequency electrical characteristics, GaN transistors have become one of the most popular candidates for next-generation high-efficiency high-voltage switching devices. However, the current collapse effect of GaN transistors limits its application. Researchers mainly use the double pulse, DLTS etc, to characterize the current collapse effect. These methods can not simply and directly distinguish the defect level from the passivation layer or the GaN buffer layer that causes the current collapse. In addition, shallow energy level analysis that affects the high frequency performance of GaN is also rarely reported in the literature. The applicant of the project innovatively proposes a method of back-grid synchronous high-voltage pulse deep level transient spectrum. The influencing factors of the interface state in the surface passivation layer are shielded by the two-dimensional electron gas unique to the GaN heterojunction. As well as the physical mechanism of the back-gate charge coupling, and using an independently designed high-voltage fast pulse generation circuit, the current collapse mechanism caused by the shallow energy level of the gallium nitride buffer layer is studied. By establishing the relationship between the buffer layer structure and the effect of defect density on carrier transport characteristics, the relationship between doping, structure and current collapse of the buffer layer is revealed, and the mechanism of current collapse in the device is finally identified to improve the epitaxial wafers. Finally, this investigation can be the basis of auxiliary epitaxial wafer design and growth.

凭借优良的抗击穿、低导通和高频率电学特性，氮化镓晶体管已经成为下一代高效高压开关器件的热门候选者之一。然而氮化镓晶体管特有的电流崩塌效应限制了其发展。国内外研究者主要通过双脉冲、DLTS等方法表征电流崩塌效应。这些方法不能简单、不能直接厘清引起电流崩塌的因素是来自钝化层还是氮化镓缓冲层的缺陷能级，另外文献中也鲜有报道影响氮化镓高频性能的浅能级分析。本项目申请人创新性的提出一种背栅同步高压脉冲深能级瞬态谱的方法，通过氮化镓异质结特有的二维电子气屏蔽来自表面钝化层中的界面态的影响因素以及背栅电荷耦合的物理机制，并利用自主设计的高压快脉冲发生电路，研究氮化镓缓冲层浅能级引起的电流崩塌机理。通过建立缓冲层结构以及缺陷密度对载流子输运特性影响的关联模型，从而揭示出缓冲层材料掺杂、结构与电流崩塌的关系，最终明确引起器件中电流崩塌的机理，为提高外延片的动态性能和辅助外延片的生长与设计提供有效的物理依据。

氮化镓器件是近些年来非常热门的一个研究方向，因为氮化镓器件具有高击穿、低导通和高频率的特性，大量应用于5G通信。在项目执行期内，针对氮化镓特有的电流崩塌问题，开展了低欧姆接触电阻、低动态电阻的研究。一方面发现外延缺陷与器件电流崩塌具有非常大的关系，比如位错，掺杂浓度等因素，另一方面，在工艺过程中也会对器件电流崩塌产生影响，比如钝化工艺、高温欧姆接触等。通过这两方面的研究结果，厘清了导致电流崩塌的两个因素，为实现低动态电阻的器件提供了有效支撑，也为器件的可靠性提供良好的思路。