Light emission and the quantum efficiency of lateral p-n junctions on patterned GaAs (100) substrates

Abstract

We have studied the light emission from lateral p-n junctions grown by MBE on patterned GaAs (100) substrates. The junctions were located at the upper and lower boundaries between (100) flat/(311)A facet combinations. Electrical measurements showed that, under low bias, tunnelling dominated the current flow, but the level was sample- and junction-dependent. We attribute these differences to growth-dependant Ga migration rates at the flat-facet interfaces, with consequent formation of mid-gap states which assist in the tunnelling process. Above approximately 0.5 V forward bias, the diffusive current component became dominant, although partly masked by non-linear series resistance effects. In this higher voltage regime, significant light emission was observed, particularly from the lower p-n junctions. The external quantum efficiencies varied from approximately 0.1% for the upper junctions to as high as 7.3% for the best lower junction. This difference was correlated with the degree of tunnelling, suggesting that the mid-gap states involved in this process can also act as non-radiative recombination centres for the diffusively injected carriers.