Effect of strain relaxation on the drain conductance in AlGaN/GaN HEMTs

Abstract

The aim of this work is to study the potential offered by microwave power in the device Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-m</sub> N/GaN HEMT. The effects of technological and electrical parameters such as the aluminum mole fraction "m", the thickness of the AlGaN doped layer "d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> " and doping concentration "N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> " in the output conductance are studied taking into account the effects of spontaneous and piezoelectric polarizations in the heterojunction AlGaN/GaN and the relaxation of the crystal lattice induced by the aluminum mole fraction. We presented an analytical model for the electrons concentration "n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> " in the 2DEG and the current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> in the channel for strong inversion regime by solving the Poisson equation and Schrödinger self-consistent calculations. From the analytical model of the current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> including the effects of spontaneous and piezoelectric polarizations, and lattice relaxation, the output conductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> according to the voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> are deduced. We note that, the increasing of "m" and "N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> " increase the carrier density "n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> " in the 2DEG. Although, the increase of the doped layer thickness increases the output conductance. The influence of the crystal lattice relaxation on the electrical performance acts directly on the threshold voltage if the value of the mole fraction exceeds 0.38.