Improved performance of submicrometer-gate GaAs MESFETs with an Al 0.3Ga0.7As buffer layer grown by metal organic vapor phase epitaxy

Submicrometer-gate MESFETs were fabricated with a GaAs active layer and an Al_xGa_1-xAs buffer layer grown by metalorganic vapor-phase epitaxy. To investigate the effect of buffer layer composition on device performance, microwave FETs with GaAs and Al _0.3Ga_0.7As buffer layers were compared. Electron Hall mobility in the n-GaAs active layer was found to be unaffected by the Al content or carrier concentration in the buffer layer. However, a considerable improvement in the maximum available gain to as much as 5.2 dB was obtained at 26.5 GHz for FETs with a p-Al_0.3Ga_0.7 As buffer layer; this was 1.5 dB higher than the gain obtained with a p-GaAs buffer layer. The improvement is due to a 20-30% reduction in both drain conductance and drain-gate capacitance