Modulation Doped FETs

Abstract

AbstractOperation and technology of conventional and pseudomorphic modulation‐doped field‐effect transistors (MODFET s) based on conventional semiconductors, SiGe/Si heterostructures, and recently popularized III–V nitride semiconductors are treated. While conventional AlGaAs/GaAs MODFET represent the genesis of these highly successful devices, pseudomorphic MODFET s (PMODFET s) exhibit additional degrees of freedom in the choice of channel composition. This added degree of freedom has led to device structures that can be tailored to a particular application with significant improvement in performance. Experiments carried out with AlGaAs/InGaAs/GaAs and InAlAs/InGaAs/InP PMODFET s demonstrate that these devices are superior to their counterparts with lattice‐matched channels. MODFET s with unprecedented performance, for instance, with a power gain of 7.3 dB at 140 GHz and a noise level of 1.4 dB in the 90‐GHz range, are described. The advent of high‐quality SiGe layers on Si substrates has paved the way to the exploration and exploitation of heterostructure devices in a Si environment. MODFET s based on the Si/SiGe have been achieved with extraordinary p‐channel performance. With 0.25‐μm gate lengths, the current gain cutoff frequency is about 40 GHz. When the gate length was reduced to 0.1 μm, the current gain cutoff frequency increased to about 70 GHz. Finally, owing to their large bandgaps, large high field electron velocity, large breakdown fields, large thermal conductivity, and robustness, wide‐bandgap nitride semiconductors have paved the way to AlGaN/GaN MODFET s with superior power performance. CW power levels of about 6 W have been achieved at 10 GHz in devices with 1 mm gate periphery that are comparable to power densities extrapolated from smaller devices. When four of these devices were power combined in a single‐stage amplifier, a CW output power of 22.9 W with a power‐added efficiency of 37% was demonstrated at 9 GHz. On the noise figure front, a minimum noise figure for a 1‐mm device of 0.85 dB with an associated gain of 11 dB at 10 GHz was obtained.