ABSTRACT
The reason for calling the device as a high-electron-mobility transistor (HEMT) is explained in this chapter. In addition, the numerical magnitudes of the high mobilities attained in HEMTs are mentioned to illustrate what exactly the high mobility means. The superiority of HEMTs over MESFETs and MOSFETs in the context of mobility is clarified. The idea of modulation doping and its advantage are described. The phenomena taking place at the heterojunction interface and the generation of 2D electron gas are dwelled upon. A depletion HEMT (dHEMT) has a pre-existing channel while in an enhancement HEMT (eHEMT), the channel is produced by applying a gate voltage. The main steps of the non-aligned and aligned gate HEMT processes are outlined. The difference between pseudomorphic and metamorphic HEMTs is explained. The time-independent Schrodinger equation is solved to get the energy levels in the quasi-triangular well produced at the heterojunction of the HEMT. The implicit equation for electron sheet charge in a HEMT is obtained by adding together the energy components contributing to the discontinuity of conduction band edge at the heterojunction. Features of the linear charge-control model of HEMTs are presented.
