ABSTRACT
The electrostatics of the heterojunction results in the formation of a triangular well at the interface, which confines the electrons in a two-dimensional (2D) electron gas (2DEG). The separation of the 2DEG from the ionized donors significantly reduces ionized impurity scattering resulting in high electron mobility and saturation velocity. The current control mechanism in the high electron mobility transistors (HEMT) is control of the 2DEG density at the heterojunction interface by the gate voltage. The 2DEG density can be maximized by using planar doping in the donor layer and by increasing the conduction band discontinuity at the barrier/2DEG interface. The frequency at which a HEMT operates is limited by the electron transit time from the source to the drain. Breakdown voltage is an important parameter for power devices. A device with high breakdown voltage can be biased at high drain voltages, which increases the drain efficiency, voltage gain, and power added efficiency.
