Effect of LT-layer thickness on the performance of LT-GaAs and LT-Al0.3Ga0.7As MISFETs

Abstract

GaAs MISFETs with low temperature (LT) grown gate insulator layers have been fabricated and their electrical properties analyzed. The transconductance frequency dispersion characteristics of thinner (250 angstroms and 500 angstroms thick) LT-GaAs and LT-Al0.3Ga0.7As MISFETs are better than those of thicker (2000 angstroms and 1000 angstroms thick) LT-GaAs MISFETs. LT-Al0.3Ga0.7As and thinner LT-GaAs samples exhibited 1/f noise, while thicker LT-GaAs samples exhibited 1/f3/2 noise with 500 Hz corner frequency. The noise parameter αlatt was found to be of the order 10-4 for thinner LT-GaAs samples and for all of the LT-Al0.3Ga0.7As samples. From the DC characteristics, it was found that thinner LT-layer insulators are ideal for achieving higher transconductance without sacrificing the RF power handling capability. Our simulation results on 500 angstroms thick LT-Al0.3Ga0.7As MISFET devices showed power handling capability of 1.8 W/mm for a gate bias of -2 V and drain bias of 18.5 V at 1.1 GHz.