Deep Levels in Al(x)Ga(1-x)As:Fe Single Crystals

摘要

Deep levels are energy levels in the bandgap of a semiconductor with activation energies which are large compared to kT. At a deep defect, the carrier wavefunction is localized near the site of the defect and, hence, delocalized in k-space. The defect can couple to a variety of phonons and interacts strongly wit the lattice. Deep states generally tend to be nonradiative centers. Physically, they could result from certain chemical impurities, native defects such as vacancies, complexes involving native defects and impurities, surfaces, and interfaces. A variety of deep centers are almost always present in semiconductor crystals. They may be introduced intentionally into a semiconductor crystal by various methods. Gold introduces a deep acceptor level and a deep donor level in silicon. Gold may be evaporated onto the surface of a silicon wafer and then diffused-in by heating the wafer at a temperature of the order of 900 C for several minutes so that the gold atoms distribute themselves uniformly in the silicon crystal. Impurities like chromium and iron may be added to the melt from which GaAs, Al sub x Ga(1 sub x)As, and other semiconductors are grown by liquid phase epitaxy. Heat treatment and bombardment by energetic electrons also create deep centers in semiconductors. Deep levels affect device performance in many ways.