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

A strong piezoelectric effect and a large spontaneous polarization allow one to incorporate a large electric field (> 10(6) V/cm) and high sheet charge (> 10(13) cm(-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 similar to 4x10(19) cm(-3). This work suggests that very interesting tunnel junctions can be made from undoped AlGaN/GaN heterostructures. (C) 2000 American Institute of Physics. [S0003-6951(00)05138-X].