Natural ageing effects of Schottky-gate GaAs FETs in current-voltage characteristics and in 1/f noise spectrum

Abstract

We study the current-voltage (I–V ) characteristics and 1/f (flicker) noise spectra of experimental samples (prototypes) of submicron GaAs field-effect transistors (FETs) with Schottky planar gate in the linear regime. The model of I–V characteristics, in which the FET channel is described by the Shockley model and the crowding of current lines in passive regions is taken into account, is proposed. Analysis of the measured set of I–V characteristics allowed us to define geometric and electric parameters of the devices more precisely. The natural ageing effects were revealed by analyzing the measurements performed at a 3-year interval. We make the conjecture that excess defects are present in the structure and they are probably represented by dipoles (donor-acceptor pairs). Concentration of excess defects is estimated and its significant decrease with time is detected. For analysis of 1/f noise, we used the hypothesis of the existence of bistable point defects, assuming that the latter result in resistivity fluctuations of the conducting regions. It is shown that defects in the channel give the main contribution to 1/f noise and their concentration decreases with time. Increased content of defects near the buffer layer was detected in some devices. The experimental data obtained allow us to suppose that the observed 1/f noise is caused by the excess defects revealed in the analysis of I–V characteristics of FETs with Schottky planar gate.