On the temperature variation of threshold voltage of GaAs MESFETs

The authors have investigated the temperature dependence of the threshold voltage of depletion-mode GaAs MESFETs with epitaxially grown n channels. An approach to threshold shift analysis that allows direct comparison with threshold measurement is taken. The contributions from various temperature-dependent effects to the threshold-voltage shift were studied, including the built-in voltage of the Schottky barrier, deep-level transients, capping layer effects, the substrate-channel built-in voltage, and the k factor which is related to channel mobility. A quasi-DC method for threshold voltage measurement, which enables threshold voltage to be measured as a function of temperature with minimum deep-level transient effect is reported. A method has also been developed to measure the temperature dependence of built-in voltage which is completely free from transient effects. The results show that the major contributors to the temperature variation of threshold voltage are the temperature dependence of the Schottky barrier built-in voltage and the effect of the capping layer