P-GaSb/n-GaAs heterojunctions for thermophotovoltaic cells grown by MOVPE

Abstract

The reverse bias dark current of p-GaSb/n-GaAs junctions has been found to be unexpectedly low despite the 7% lattice mismatch between the layers. 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. Here we present a study of the characteristics of diodes grown at different temperatures and with varying GaSb doping levels. Diodes were grown at temperatures ranging from 500–550 °C using TMGa and TMSb. Several orders of magnitude reduction in reverse bias dark current was observed across this narrow temperature range. The ‘turn-on’ voltage also increases with reduction in growth temperature. Under illumination Voc reached a maximum...