Analysis of GaN cap layer effecting on critical voltage for electrical degradation of AlGaN/GaN HEMT

¹ Key Lab of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, PO Box 912, Beijing 100083, P.R. China
² Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, PO Box 912, Beijing 100083, P.R. China
³ ISCAS-XJTU Joint Laboratory of Functional Materials and Devices for Informatics, Xi’an 710049, P.R. China

^a e-mail: xlwang@semi.ac.cn

Received: 15 January 2014
Revised: 25 June 2014
Accepted: 14 August 2014
Published online: 10 October 2014

Abstract

We present calculation of critical voltage for AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layer. The calculation includes mechanical stress and relaxable energy in the GaN/AlGaN barrier layer. Under high voltage conditions, the high electric field results in an increase in stored relaxable energy. If this exceeds a critical value, crystallographic defects are formed. This degradation mechanism is voltage driven and characterized by a critical voltage beyond which non-reversible degradation takes place. The dependence of the GaN cap layer’s thickness on the critical voltage has been discussed. The calculated results indicate that thicker GaN cap layer results in higher critical voltage.