Effect of GaSb growth temperature on p-GaSb/n-GaAs diodes grown by MOVPE

Despite the 7% lattice mismatch, the reverse bias dark current of p-GaSb/n-GaAs junctions has been found to be unexpectedly low. MOVPE-grown diodes exhibited dark currents up to two orders of magnitude lower than comparable GaSb homojunctions. The initial nucleation of GaSb on GaAs was found to play an important role in determining the properties of the bulk layer. A larger number of small nucleation sites produced diodes with lower reverse bias leakage currents and growth temperature was in turn critical in determining the size of these nucleation islands. The authors present a study correlating growth temperature with nucleation site density, dark current and open circuit voltage under illumination. Diodes were grown at temperatures ranging from 490-550°C using TMGa and TMSb. A reduction in reverse bias dark current of several orders of magnitude was observed across this narrow temperature range. The `turn-on' voltage also increased with reduction in growth temperature and there was a corresponding increase in the average open voltage, Voc, under illumination. However, Voc did exceed ~0.25 V. This is low compared to GaSb homojunctions (typically 0.45 V) and it may be limited by a low shunt resistance under illumination as well as low efficiency from the thin GaSb layers. Other alkyls [TIPGa and t-DMASb], which allow a further reduction in growth temperature, are being investigated