The linearities of pseudomorphic Al0.3Ga0.7As/ In0.2Ga0.8As doped-channel FET's were characterized by comparing the characteristics of modulation-doped field-effect transistors (FET's) based on de 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.
