Polarization effects and transport in AlGaN/GaN system

The AlCaN/GaN heterostructure is important for both electronic and optoelec tronic devices. In addition to having a large band gap, the heterostructure has a strong piezoelectric effect and a large spontaneous polarization. Th is allows one to incorporate a large electric field (> 10(6) V/cm) and high sheet charge (>10(13) cm(-2)) without doping, Theoretical studies are done to examine how polarization effects controls the sheet charge density. The studies also focus on how interface roughness, aluminum mole fraction in t he barrier, impurity scattering, sheet charge density, and phonon scatterin g influence mobility. Results are compared with experimental studies on sam ples grown by both molecular beam epitaxy (MBE) and metalorganic chemical v apor deposition (MOCVD). We find that interface roughness is a dominant sou rce of scattering in the samples reported. Due to the variation in growth t echniques we find that the MBE samples have a smoother interface quality co mpared to the MOCVD samples. By carefully fitting the experimental data we present results on interface roughness parameters for MBE and MOCVD samples . (C) 2000 American Vacuum Society. [S0734-211X(00)07204-8].