A surface-potential based compact model for GaN HEMTs incorporating polarization charges

Abstract

High electron mobility transistors (HEMTs) based on III-nitride semiconductor heterostructures are being actively pursued for high-voltage and high-speed microwave applications [1]. As discrete GaN transistors move towards integration in circuits, a compact model for device operation is highly desirable to aid systematic design. GaN HEMTs differ from Silicon and other III-V FETs through the presence of high density polarization-induced sheet charges at heterostructure interfaces. Till date, no clear method exists to incorporate such polarization charges into compact modeling of HEMTs. We introduce a method for incorporating polarization sheet charges into compact modeling in transistors. The Poisson equation is solved directly with a Dirac-delta function sheet charge at the heterojunction to obtain an analytical equation for the surface potential. This surface potential is then used to calculate the HEMT characteristics. Thus, the results of this work for the first time make an explicit connection between the material properties of the HEMT heterostructure with a surface potential based compact model through the polarization sheet charge. Furthermore, we have extended the intrinsic model by including field-dependent mobility and velocity saturation. The developed model should prove helpful in designing of devices and circuits.