GaAs MESFET's with Ga1-xAlxAs buffer layers

MESFET's were fabricated with GaAs active layers and Ga
1-x
Al
x
As buffer layers grown by metallorganic vapor-phase epitaxy on semi-insulating substrate Ga
1-x
Al
x
AS buffer layers with x = 0.2, 0.4, and 0.6 were used to determine the effect of buffer-layer composition on device performance. While very high transconductance values (175 mS/mm) were obtained with buffer layers with x = 0.2, the transconductance decreased with increase of aluminum composition in the buffer layer. The decrease in transconductance may be due to an observed reduction of electron mobility in the active layer with increasing aluminum concentration in the buffer layer.