等离子体刻蚀凹栅槽影响AlGaN/GaN HEMT栅电流的机理

Effect of Plasma Dry Etching on Gate Leakage of Recessed AlGaN/GaN HEMTs

对等离子体干法刻蚀形成的凹栅槽结构Al GaN/GaN HEMTs肖特基电流增加的机理进行了研究.实验表明,凹栅槽结构Al GaN/GaN HEMTs肖特基栅电流增加一个数量级以上,击穿电压有一定程度的下降.利用AFM和XPS的方法分析Al GaN表面,等离子体干法刻蚀增加了Al GaN表面粗糙度,甚至出现部分尖峰状突起,增大了栅金属与Al GaN的接触面积;另一方面,等离子体轰击使Al GaN表面出现一定量的N空位,相当于栅金属与Al-GaN接触界面处出现n型掺杂层,使肖特基结的隧道效应加强,降低了肖特基势垒.由此表明,Al GaN表面粗糙度的增加以及一定量的N空位出现是引起栅电流急剧增大的根本原因.

The mechanism for increasing gate leakage current in recessed-gate A1GaN/GaN HEMTs, which are fabricated successfully by plasma dry etching,is investigated. Compared with conventional planar FETs,the gate leakage current of the recessed-gate A1GaN/GaN HEMTs increases by 10 times, and the breakdown voltage decreases to some extent. AFM and XPS are employed to measure the A1GaN surface before and after etching. The A1GaN surface becomes rougher, and even some protuberances like awl appear during dry etching. Thus the contact area between the metal and the semiconductor increases for the rougher A1GaN surface. On the other hand,some N vacancies generate plasma bombarding during dry etching. The N vacancies,which enhance the tunneling effect and reduce the Schottky barrier height, are regarded as n-type doped in the etched A1GaN surface. All these experiments indicate that the significant increase in the gate leakage current is due to the in- creased roughness and the appearance of these N vacancies in the A1GaN surface.