OFF-State Drain-Voltage-Stress-Induced <i>V</i> _TH Instability in Schottky-Type p-GaN Gate HEMTs

Abstract

In this article, we systematically investigate the OFF-state drain-voltage-stress-induced threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> ) instability in Schottky-type p-GaN gate high electron mobility transistors (HEMTs). OFF-state drain-voltage stress and recovery tests were conducted under various temperatures and different drain biases. A sharp increase in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> was observed at the beginning of the stress, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> kept shifting positively during the stress until it reached saturation. Further experiments showed that two different mechanisms dominated the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> shift, which were distinguished by the temperature dependence, degradation/recovery process and affected locations in the gate region. The hole deficiency caused by hole emission from the p-GaN layer is suggested to be the dominant reason for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> instability at the beginning of the stress, while with increasing stress time, electron trapping in the barrier and buffer layers gradually dominates the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> shift. Based on the identified mechanisms, physics-based analytical calculations and empirical fitting are conducted to describe the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> behavior during the OFF-state drain-voltage stress. The fundamental mechanisms can provide a guide to develop corresponding methods to address the drain-induced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> instability issue.