Electrical properties and origin of deep levels in undoped InAlAs layers grown by MOCVD

Undoped InAlAs layers grown by MOCVD (metal-organic chemical vapor deposition) were studied to elucidate the background carrier behavior. The activation energies of these carriers were estimated by Hall measurements (about 140 meV). Three deep levels, A (0.5 eV), B (0.3 eV), and C (0.07 eV), were detected by deep-level transient spectroscopy. The concentrations of these deep levels rapidly increased with decreasing Ts. The concentrations of the deep levels have been found to have similar dependence with N/sub D/-N/sub A/. These results indicate that N/sub D/,-N/sub A/ originated from deep levels which act as deep donors. O impurities in undoped InAlAs layers were shown by secondary ion mass spectroscopy to be very high. O impurities are thought to form complexes with defects which act as donors in InAlAs. The electrical properties of undoped InAlAs layers grown by MOCVD are reasonably explained using this mechanism. The use of pure source materials and a leak-tight system is important in order to obtain high-quality InAlAs layers.<>