Bismuth Surfactant Enhancement of Low-Temperature MBE-Grown GaSb Thin Films

Homoepitaxial growth of GaSb is crucial for applications in mid-IR optoelectronics, such as thermal imaging, optical communication, LEDs, and thermophotovoltaic cells. At cold growth temperatures, the surface of GaSb degrades and can result in surface defects and device performance degradation. Yet, lower growth temperatures are favorable for reasons ranging from compatibility with other layers that require low-temperature growth to lowered bulk mobility to prevent defects. Recently, we have demonstrated that bismuth surfactancy can lead to a smoother surface morphology of low-temperature-grown GaSb films. In this work, we examine the effects of bismuth surfactant at varying fluxes on the film quality of GaSb(100) grown at a cold temperature of 290 degee Celcius using molecular beam epitaxy (MBE). <br/><br/>A series of 200nm thick GaSb is grown via MBE in a Veeco GENxplor system in otherwise identical growth conditions except for the variation of the bismuth surfactancy flux used during growth. All films are grown at the stoichiometric point at ~0.4 monolayer (ML) per second. Bi:V flux as measured by the beam flux monitor (BFM) is varied from 0, no bismuth, to 0.2, where we have found an observable (1%) Bi incorporation. The effects of bismuth surfactant on the GaSb surface are characterized by atomic force microscopy (AFM). Raman spectroscopy is used to characterize and compare the film quality. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are used to analyze film surface and surface composition. High-resolution X-ray diffraction (HRXRD) was performed to confirm the bismuth incorporation into the films.<br/><br/>We concluded in our previous findings that bismuth substantially increases the two-dimensional Erlich-Schwöebel (ES) potential barrier of atomic terraces, inducing an upward adatom flux that contributes to surface smoothing. This work examines the effects of such bismuth surfactancy over a wide range of bismuth fluxes from none to some incorporation to understand how bismuth surfactancy can enhance the surface morphology and film structure of low-temperature grown GaSb. Furthermore, this research can potentially improve the growth of other homoepitaxial III-V semiconductor systems under non-ideal conditions and will contribute to the understanding of the bismuth surfactancy effects in dilute GaSbBi alloys.