We report the growth and photoluminescence study of very high quality AlxGal-xAs layers grown by molecular beam epitaxy over the 0<x<0.38 composition range. Heterostructure doped-channel FET's (DCFET's) manufactured using pseudomorphic AlGaAs/InGaAs/GaAs heterostruc-tures containing such a layer have produced an output power of about 1 W/mm with 7.8 dB small signal gain and 60 % power-added efficiency at 18 GHz
