Pseudomorphic AlGaInP/GaAs MODFETs, novel device concepts for simple fabrication schemes

A novel device concept of an AlGaInP/GaInAs/GaAs MOdulation Doped Field Effect Transistor (MODFET) has been developed. Two characteristic features have been incorporated in the device structure: An AlGaInP barrier which provides a larger conduction band offset than the commonly used AlGaAs and a highly carbon-doped p-type GaAs gate structure which supports a very simple, self-aligned fabrication scheme. Using 1 micrometer optical lithography we have fabricated first demonstrator devices with a current gain cut-off frequency of 60 GHz and a power gain cut-off frequency of 140 GHz. In addition, the devices show large gate-drain diode breakdown voltages in excess of 30 V and gate currents as low as 50 nA even a gate-source voltages of minus 5 V.