Examination of tunnel junctions in the AlGaN/GaN system: Consequences of polarization charge

Abstract

A strong piezoelectric effect and a large spontaneous polarization allow one to incorporate a large electric field ${\text{(>10}}^6 \mathrm{V/cm})$ and high sheet charge ${\text{(>10}}^{13} {\mathrm{cm}}^{\mathrm{-2}})$ without doping in the AlGaN/GaN heterostructure. Theoretical studies are done to examine how polarization effects can be exploited to design metal–AlGaN/GaN tunnel junctions. We find that with a proper choice of AlGaN thickness undoped junctions can be made with very high metal to two-dimensional electron gas tunneling. Thus, a Schottky junction can be converted to a tunnel junction without doping. The tunneling probabilities approach those produced in a system doped at ${\text{∼4×10}}^{19} {\mathrm{cm}}^{\mathrm{-3}}.$ This work suggests that very interesting tunnel junctions can be made from undoped AlGaN/GaN heterostructures.