An AlGaAs/InxGa1-xAs/AlGaAs (0⩽x⩽0.5) pseudomorphic HEMT on GaAs substrate using an Inx/2Ga1-x/2As buffer layer

A pseudomorphic HEMT employing a thick In_x/2Ga_1-x/2As buffer layer on a GaAs substrate substrate is proposed in order to use an In_xGa_1-xAs 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 4.6×10¹² cm^-2 was obtained at x=0.4 with a high electron mobility of 15500 cm²/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-μm gate length was 500 mS/mm at room temperature, which was about 2.5 times larger than that of x=0