Modulation‐Doped Field‐Effect Transistors (MODFET)

Abstract

Conventional modulation‐doped field‐effect transistors (MODFETs) with unprecedented performance, e.g., a power gain of 15 dB at 190–235 GHz and a noise level of 1.2 dB with 7.2‐dB gain in the 90‐GHz range, have been demonstrated. Passivation process is of fundamental importance in the stability, good performance, and extension of device operative lifetime. We discuss strategies used to passivate the surface of GaAs and related compounds and GaN in the context of FETs. Recent research on the enhancement‐mode PMODFET (E‐PMODFET) variety for applications in high‐speed and low‐power digital circuits, and power amplifiers with single power supply is described. Reliability of MOSFET based on GaAs is reviewed to some extent. Scalability issues as well as progress in FinFET‐based on InGaAs channel are summarized. Also to be noted is that III–V compound semiconductors as alternative to Si as the channel material to improve the performance of metal‐oxide–semiconductor field‐effect transistors (MOSFETs) on Si platforms is a very attractive option for the next‐generation high‐speed integrated circuits but faces serious challenges because of the lack of a high‐quality and natural insulator. III‐V Nitride‐based HFETs showed tremendous performance in both high‐power RF and power‐switching applications. AlGaN/GaN based high power HFETs on SiC substrate with 60 nm gate lengths have achieved maximum oscillation frequency of 300 GHz. On‐resistance of 1.1∼1.2 Ω·mm as well as drain current of ∼0.9 A/mm was also achieved. For HFET devices operated in Class AB mode on GaN semi‐insulating substrates, a continuous wave power density of 9.4 W/mm was obtained with an associated gain of 11.6 dB and a power added efficiency of 40% at 10 GHz. III‐Nitride devices for power switching application has achieved near theoretical limit for vertical devices based GaN native substrates, and breakdown voltage as high as 1200 V and on resistance as low as 9 mΩ‐cm2 for lateral HFET devices on low‐cost silicon substrates. For AlGaN/GaN HFETs on high‐resistivity silicon substrates, promising results were also demonstrated. Because of the much larger 2DEG density in lattice‐matched InAlN/GaN HFETs, drain current as high as 2 A/mm was demonstrated, and the highest current gain cutoff frequency of 370 GHz was also reported on 7.5‐nm‐thick In In0.17Al0.83N barrier HFETs. Despite the above‐mentioned encouraging achievements, the degradation mechanisms are still not clear, which requires further investigation. The advent of high‐quality SiGe layers on Si substrates has paved the way for the exploration and exploitation of heterostructure devices in a Si environment. MODFETs 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.