Epitaxial phases of high Bi content GaSbBi alloys

TL;DR

This paper investigates how the Sb/Ga flux ratio influences the structural quality and Bi incorporation in GaSbBi alloys, identifying optimal growth conditions for high-quality mid-infrared optoelectronic materials.

Contribution

It reveals the critical role of the Sb/Ga flux ratio and temperature in controlling epitaxial phases and Bi incorporation in GaSbBi alloys, providing a framework for high-quality crystal growth.

Findings

Three distinct epitaxial phases identified based on Sb/Ga flux ratio.

Optimal growth window determined by temperature and flux ratio.

High Bi content up to 14.5% achieved with controlled conditions.

Abstract

GaSbBi alloys have recently emerged as attractive materials for mid-infrared optoelectronics owing to strong band gap reduction enabled by Bi incorporation into the GaSb matrix. The fundamental understanding of the epitaxial process required to demonstrate high quality crystals is in an early-developmental phase. From this perspective, we report on the key role played by the Sb/Ga flux ratio in controlling the structural quality and incorporation of high Bi content (up to 14.5 %-Bi), revealing three distinct epitaxial phases. The first phase (below stoichiometric Sb/Ga) exhibits Ga-Bi compound droplets, low crystal quality, and reduced Bi content. At the second phase (above stoichiometric Sb/Ga), the crystal exhibits smooth surfaces and excellent crystallinity with efficient Bi incorporation. The last phase corresponds to exceeding a Sb/Ga threshold that leads to reduced Bi incorporation, Bi droplets and degraded crystallinity. This threshold value that defines the optimal growth window is controlled by the temperature as well as the Bi/Ga ratio. Increasing temperature increases the threshold, albeit simultaneously reducing Bi incorporation. Conversely, increasing the Bi/Ga flux ratio increases Bi incorporation, while narrowing down and ultimately closing the window. This study provides a general framework enabling development of high quality GaSbBi heterostructures for emerging mid-infrared optoelectronics.