WSix refractory metallization for GaAs metal–semiconductor field-effect transistors

Abstract

WSix thin films on GaAs substrates have been investigated for potential use as refractory gates for self-aligned metal–semiconductor field-effect transistor (MESFET) devices. Films with Si/W ratio in the range of 0.19 to 1.76 have been dc magnetron cosputtered. The deposition parameters were optimized to produce adherent films with low stress and minimal impurity content. In order to serve as a refractory gate, the WSix film should perform as a diffusion barrier. The WSi0.45 films satisfied this requirement by having the highest crystallization temperature of 875 °C. Such films remained amorphous following the high-temperature dopant activation annealing (800 °C), thus reducing Ga and As outdiffusion and preventing pit formation in GaAs under the gate. I–V and C–V measurements were used to characterize contact electrical properties such as barrier height, ideality factor, and carrier concentration. A simulated threshold voltage shift for MESFET structure was obtained by modeling diode results. The WSi0.45 films were characterized by the most stable Schottky contact to GaAs (φB =0.75 eV, n=1.1) and showed minimal shift in carrier concentration and threshold voltage after annealing at 800 °C. In addition, the effect of impurities on contact properties was investigated. The presence of Zn at the WSix/ GaAs interface caused drastic reduction in carrier concentration and increased Schottky barrier height up to 0.9 eV.