Introduction to High Electron Mobility Transistors

Abstract

High electron mobility transistors utilize quantum phenomenon to conduct charge. At the interface of a type -I heterojunction, a triangular quantum well is formed, in which electrons are confined to bound energy states. These bound energy states form a 2DEG. Due to reduced scattering mechanisms, the carrier mobility is large. A HEMT’s operation is constrained by two threshold voltages, to create 2DEG and then to control gate. Based on the electrical conduction behavior, a normally on HEMT is classified as a depletion mode HEMT and a normally off HEMT is called as enhancement mode HEMT. Depending on the structure, pHEMT and mHEMT are two fundamental classifications. An induced HEMT is a HEMT which uses III-V nitrides. InP HEMTs shows superior transistor gain, transition frequency, and low noise behaviour. GaAs substrate based HEMTs are omnipresent due to their cost advantage and GaN based HEMTs are useful for high-power, high frequency and low noise systems.