New high-speed (Al, Ga) as modulation doped field-effect transistors

Recent advances in the fabrication technology of compound semiconductors have made possible the development of a new type of device called the modulation doped field-effect transistor (MODFET) which is capable of higher speeds than conventional FETs because its conduction electrons can move faster. These higher electron velocities in MODFETs are due to the fact that the electrons are spatially separated from ionized donors which leads to a reduction in scattering. By utilizing this enhanced velocity in real devices, substantial performance improvements in both microwave and digital circuits have been obtained. Subnanosecond access times for 1 Kb static random access memory and frequency division at 13 GHz have been obtained in MODFET-based digital circuits. In the microwave area, MODFETs show great promise in low-noise amplifier applications, as noise figures for MODFETs operated at 300K are below 0.6 dB at 8 GHz.