Thermal Degradation Mechanism of Au/Pt/Ti/GaAs Schottky gate of MESFETs

Thermal degradation mechanisms of the GaAs MESFETs have been studied using FATFET(Lg=50¿, Wg= 200¿m) with thermal step stress and accelerated life tests. The I-V and C-V characteristics of the devices were measured after every thermal step. AES, XRD and cross-sectional TEM were also used to analyze the thermal degradation mechanisms. The activation energy for thermal degradation of the Schottky contact and a mean-time-to-failure (MTTF) in accelerated life tests are evaluated to be 1.3 eV and 2 × 10⁸ hours at 125°C, respectively. The degradation of Au/Pt/Ti/GaAs Schottky contact is due to the decrease of the net electron concentration by the excess VGa and the effective channel thickness by the formation of TiAs compound at the interface. Their activation energies are determined to be 1.4 eV and 1.74 eV, respectively. The activation energy for the decrease of the net electron concentration, 1.4 eV, is nearly consistent with that obtained by MTTF test, 1.3 eV. At a lower temperature, at least lower than 350°C, the degradation of the Schottky contact is resulted from the decrease of net electron concentration caused by out-diffusion of host atoms of GaAs and, at the higher temperature, the reduction of effective channel thickness induced by formation of TiAs is dominant for the degradation.