The n(+)-AlGaN/p(+)-4H-SiC/n-4H-SiC HBT structure possesses large interfacial polarization charges as well as bulk and interfacial defects. Considerable leakage currents have thus far prevented significant development of this device. The piezoelectric polarization charge can be controlled by modifying the strain in the structure and can in fact negate the spontaneous charge for an Al0.3Ga0.7N layer on 4H-SiC. Although large-area AlGaN films are relaxed above a critical thickness, nano-heteroepitaxy theory predicts that AlGaN columns can be coherently grown on sub-micron oxide openings. The electrical characteristics were calculated for HBTs with strained and relaxed (Al)GaN emitter layers. (C) 2004 Elsevier Ltd. All rights reserved.