Device linearity comparisons between doped-channel and modulation-doped designs in pseudomorphic Al/sub 0.3/Ga/sub 0.7/As/In/sub 0.2/Ga/sub 0.8/As heterostructures

The linearities of pseudomorphic Al/sub 0.3/Ga/sub 0.7/As/In/sub 0.2/Ga/sub 0.8/As doped-channel FET's were characterized by comparing the characteristics of modulation-doped field-effect transistors (FET's) based on dc and microwave evaluations. By using an undoped high-bandgap layer beneath the gate, the so-called parasitic MESFET-type conduction, which is common in HEMT's, can therefore be eliminated in doped-channel designs. Therefore, a wide and flat device performance together with a high current driving capability can be achieved in DCFET's. This linearity improvement in device performance suggests that doped-channel designs are more suitable for application in microwave power devices.