Investigation of Thermally Induced Threshold Voltage Shift in Normally-OFF p-GaN Gate HEMTs
Huan Wang, Yan Lin, Junsong Jiang, Dan Dong, Fengwei Ji, Meng Zhang, Ming Jiang, Wei Gan, Hui Li, Maojun Wang, Jin Wei, Baikui Li, Xi Tang, Cungang Hu, Wenping Cao
Abstract
In this article, the thermally 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">${V}_{\text{TH}}$ </tex-math></inline-formula> ) shift was investigated on two types of normally- OFF p-GaN gate high-electron-mobility transistors (HEMTs), featuring either an Ohmic-type or a Schottky-type gate. A positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{TH}}$ </tex-math></inline-formula> shift in a Schottky-type device and a negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{TH}}$ </tex-math></inline-formula> shift in an Ohmic-type device were observed at elevated temperatures. Temperature-dependent gate current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}-{V}$ </tex-math></inline-formula> ) and the transfer-length-method (TLM) analysis revealed that the bias condition across the p-GaN/AlGaN/GaN heterostructures was changed in both Schottky- and Ohmic-type devices as temperature increased. We propose that: 1) temperature-enhanced hole injection through thermionic emission which lowers the knee voltage of the Ohmic-metal/ p-GaN contact in Ohmic-type devices and 2) thermally enhanced gate current which enlarges the bias voltage across the Schottky-metal/p-GaN junction in Schottky-type devices, resulted in the observed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text{TH}}$ </tex-math></inline-formula> instability characteristics. The photoluminescence measurements were conducted to verify the thermally-enhanced ionization of magnesium dopants in the p-GaN and the corresponding instability issues.