AlGaN/GaN HEMTs With Thin InGaN Cap Layer for Normally Off Operation

Abstract

AlGaN/GaN HEMTs with a thin InGaN cap layer have been proposed to implement the normally off HEMTs. The key idea is to employ the polarization-induced field in the InGaN cap layer, by which the conduction band is raised, which leads to the normally off operation. The fabricated HEMT with an In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> N cap layer with a thickness of 5 nm showed normally off operation with a threshold voltage of 0.4 V and a maximum transconductance of 85 mS/mm for the device with a 1.9-mum-long gate. By etching off the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> N cap layer at the access region using gate electrode as an etching mask, the maximum transconductance has increased from 85 to 130 mS/mm due to a reduction of the parasitic source resistance.