Improved performance of submicrometer-gate GaAs MESFETs with an Al/sub 0.3/Ga/sub 0.7/As buffer layer grown by metal organic vapor phase epitaxy

Submicrometer-gate MESFETs were fabricated with a GaAs active layer and an Al/sub x/Ga/sub 1-x/As 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/sub 0.3/Ga/sub 0.7/As 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/sub 0.3/Ga/sub 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.<
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