Novel Surface Passivation Scheme by Using p-Type AlTiO to Mitigate Dynamic ON Resistance Behavior in AlGaN/GaN HEMTs—Part II

Abstract

The underlying mechanism responsible for the unique dynamic ON-resistance behavior is unified by demonstrating the presence of critical drain stress voltage, above which dynamic ON-resistance increases significantly, in different gate stacks. Metal–insulator–semiconductor (MIS)- and Schottky-gated HEMTs show similar dependence of critical voltage on various parameters, which establishes that gate-stack design has negligible impact on the observed phenomena. Furthermore, using the physical insights developed, this work proposes a novel surface passivation scheme to improve the dynamic performance of the device. The proposed surface passivation scheme uses p-type Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> O (AlTiO), which is deposited over SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> passivation (or GaN cap), and is shown to be an effective tool in improving the dynamic ON-resistance of the device by modulating the electric field in the GaN buffer. The proposed passivation scheme has avoided the critical voltage to appear for the entire drain stress voltage, stress time, and substrate bias range. Detailed computational analysis in conjunction with electroluminescence (EL) and photoluminescence (PL) studies revealed an electric field redistribution due to the p-type nature of AlTiO deposited over the surface passivation/capping layer, which is responsible for relaxed electric field profile in GaN buffer and observed improvement in dynamic performance. Besides, the new observations have further helped to understand the interplay between surface conditions and GaN buffer, defining its collective role in governing the dynamic performance of GaN HEMTs. Finally, various findings and the proposal in this work have been validated for buffers having higher carbon doping and devices with p-type AlTiO deposited over GaN cap instead of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> cap.