In situ monitoring of GaSb_1 − xBi_x growth using desorption mass spectrometry

Incorporation of bismuth into GaSb is of interest because the alloy bandgap can be substantially reduced while avoiding strain relaxation. Thus, the GaSb_1 − xBi_x alloy is potentially useful in extending the wavelength in optoelectronic devices. However, the epitaxial growth of this alloy via molecular beam epitaxy is challenging because the parameter space is relatively small. Additionally, a precise relationship between Bi incorporation and growth parameters is not well understood. In this study, the authors have utilized the in situ desorption mass spectrometry (DMS) technique to make relative measurements of Sb and Bi desorption during GaSb_1 − xBi_x growth. Employed in this material system for the first time, the authors were able to identify critical growth parameters and correlate these parameters with Bi incorporation as well as accumulation at the growth surface. Specifically, the authors used the ability of DMS to precisely adjust the Sb/Ga flux ratio in order to determine the sensitivity of Bi incorporation to this flux ratio, in particular, as it approaches unity. Additionally, the authors used DMS to provide information on the surface accumulation of Bi and how this population can be purged from the surface using an incident Sb flux. The authors found that DMS can be very useful in rapidly locating the appropriate growth parameter window for this alloy as well as identifying relationships between Bi incorporation and other parameters such as substrate temperature and incident fluxes within that window.