Devices DC, RF, and microwave power performances between Al0.3Ga0.7As/In0.15Ga0.85As double doped-channel FET (D-DCFETs), conventional doped-channel FETs (DCFETs) and HEMTs are compared with each other. Device linearity and power performance have been improved by a double doped-channel design. The D-DCFETs provides a higher current density, higher gate breakdown voltage, and improves gate operation bias range as well as frequency performance. The linear power gain and output power for D-DCFETs is 19 dB and 305 mW/mm with a power-added efficiency of 52% at Vds = 2.5 V under a 1.9 GHz operation. These advantages suggest that double doped-channel design is more suitable for a high linearity and high microwave power device applications.

A high barrier Schottky gate on InGaP/InGaAs doped-channel FETs (DCFETs) provides a high current density, high gate-to-drain breakdown voltage and a better linear operation over a wide gate bias range. However, these doped-channel devices are limited by a large parasitic resistance associated with a 20 nm thick undoped InGaP layer beneath the gate metal. In this study, we inserted a Si δ-doped layer inside this high bandgap undoped InGaP layer to reduce parasitic resistances and to enhance device DC and RF power performance. These modified DCFETs (M-DCFETs) demonstrated an output power density of 204 mW/mm, a power-added efficiency of 45%, and a linear power gain of 18.3 dB for an 1 mm gate-width device under a 2.4 GHz operation. These characteristics suggest that doped-channel FETs with a Si δ-doped layer provide a good potential for high power microwave device applications.