Influence of growth rate on charge transport in GaSb homojunctions prepared by metalorganic vapor phase epitaxy

摘要

Dark current-voltage (I-V) characteristic measurement in the temperature range from -190℃ to 65℃ was carried out on GaSb p-n homojunctions prepared by low-pressure metalorganic vapor phase epitaxy. It was shown that the charge transport mechanism in these homojunctions is strongly affected by the growth rate of GaSb epitaxial layers. Samples prepared at higher growth rate (40 nm/min.) exhibit an anomalous low-temperature peak of tunneling current which can be explained by the presence of a narrow band of energies due to high concentration of native defects, probably Ga_(Sb) antisites. The same defect levels are responsible for the generation-recombination current which dominates in these samples at higher temperatures. On the other hand, quite different behavior was found in the case of slowly grown (20 nm/min) samples. At sufficiently low temperatures, a current maximum near 50 mV of forward voltage points out a band-to-band tunneling as a prevailing transport mechanism. With increasing temperature, however, this maximum disappears as at least one side of the junction becomes nondegenerate. Combination of the tunneling via energy states in the band gap and the thermal current governs the forward I-V characteristics at higher temperatures, whereas the direct tunneling remains dominant in the reverse direction.