AlGaN/GaN HEMTs on Silicon With Hybrid Schottky-Ohmic Drain for RF Applications

In this paper, the AlGaN/GaN high electron mobility transistors on a low resistivity Si substrate with the hybrid drain structure for RF applications are analyzed in detail, based on measurements, TCAD simulation, model extraction, and delay time calculation of the transistors. Owing to the E-field redistribution of the Schottky extension, both the leakage current and the breakdown voltage can be improved. Also, the enhanced RF performance can be attributed to the reduced transit time and increased transconductance, resulting from the increased electron velocity and reduced drain depletion width. With a 3-mu m extension length and a 0.2-mu m gate length, f(T) and f(MAX) of transistors can be improved from 32.7 to 49.9 GHz (52.6%) and from 35.8 to 49.2 GHz (37.4%), respectively, with ON-OFF ratio enhancement by four orders of magnitude. The breakdown voltage was improved from 21 to 38 V (80.9%).