An AlGaAs/In/sub x/Ga/sub 1-x/As/AlGaAs (0

A pseudomorphic HEMT employing a thick In/sub x/2/Ga/sub 1-x/2/As buffer layer on a GaAs substrate substrate is proposed in order to use an In/sub x/Ga/sub 1-x/As channel with a large InAs mole fraction. This buffer layer acts as a substrate with intermediate lattice constant. Transmission electron microscopy observations revealed that good-quality crystal can be obtained using this buffer layer. An extremely large two-dimensional electron gas density of 4.6*10/sup 12/ cm/sup -2/ was obtained at x=0.4 with a high electron mobility of 15500 cm/sup 2//V-s at 77 K. HEMTs were fabricated on these wafers. The transconductance increases with increasing InAs mole fraction and shows a peak at x=0.4. The transconductance for 1.7- mu m gate length was 500 mS/mm at room temperature, which was about 2.5 times larger than that of x=0.<>