Structural and optical characteristics of epitaxially grown AlGaAsBi on GaAs for potential application in ultra-low noise avalanche photodiodes

The recent addition of Bi to GaAs has been demonstrated to be an effective method for reducing excess noise in avalanche photodiodes (APDs), owing to the significant decrease in the hole ionization coefficient. It has been proposed that the incorporation of group III elements in GaAsBi alloys, such as Al, could facilitate the development of a novel class of ultra-low noise APDs utilizing GaAs substrates. However, the structural attributes of these novel alloys have not yet been comprehensively investigated, and the inclusion of Al can potentially exacerbate the significant challenges associated with the integration of Bi into GaAs. The influence of different parameters in AlGaAsBi alloys, such as the Bi flux and III/As ratio, was examined using transmission scanning electron microscopy, Nomarsky microscopy, and photoluminescence techniques. In addition to analyzing the quality of the interfaces, particular attention has been devoted to the occurrence of volcano-shaped surface nanomotifs. Two distinct types of nano-motifs associated with Bi-Al and Ga-Al-Bi droplet formation during AlGaAsBi deposition under different conditions were characterized. The growth regimes that govern the formation of surface droplets on AlGaAsBi were significantly altered by the concomitant presence of Al.