2, Arizona State University, Tempe, Arizona, United States
III-V optoelectronic materials with tunable cutoff wavelengths are desired for the development of infrared photodetectors and emitters for several applications, including, navigation, night vision, launch detection, communications, imaging, and spectroscopy. Alloying III-V materials with the heavier element bismuth enable a greater rate of bandgap reduction without introducing high levels of strain compared to other group-V elements . The present work analyses microstructure and composition of epilayers of InAsSbBi on GaSb (100) and GaAsSbBi on GaSb (100) using high resolution and aberration corrected transmission electron microscopy techniques to evaluate the quality of the quaternary epilayers.
Several pseudomorphic, 210 nm thick, narrow bandgap InAsSbBi and GaAsSbBi layers are grown by molecular beam epitaxy on GaSb substrates at temperatures from 280 to 430 °C and are examined using transmission electron microscopy (TEM), X-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS). The samples are grown with near-stoichiometric V/III flux ratios of ~ 1.01 to aid in the incorporation of bismuth that typically surface segregates due to its large size . Cross sectional TEM samples are prepared for observation along the <110> projection using standard mechanical polishing and dimple grinding, followed by argon-ion-milling (maximum beam energy 2.3 keV) with liquid-nitrogen cooling to reduce ion-beam damage . Defect analysis based on high resolution TEM indicates excellent crystallinity with no visible defects over large lateral distances. However, surface droplets are formed during high temperature growth at 430°C. Selected area diffraction patterns and fast Fourier transforms indicate the sole presence of zinc blende crystal structure with no atomic ordering. Aberration corrected high angle annular dark field (HAADF) scanning TEM images exhibited coherent defect free interfaces and geometric phase analysis of interfaces provides interfacial strain. Normalized HAADF intensities are used to study the compositional variation of bismuth. Random RBS measurements provide the average Bi content and XRD measurements determine the lattice parameters.
 P. T. Webster, A. J. Shalindar, S. T. Schaefer, S. R. Johnson, Appl. Phys. Lett. 111, 082104 (2017).
 J. Lu, P. T. Webster, S. Liu, Y.-H. Zhang, S. R. Johnson, D. J. Smith, J. Cryst. Growth 425, 250 (2015).
 C. Wang, S. Tobin, T. Parodos, J. Zhao, Y. Chang, S. Sivananthan, D. J. Smith, J. Vac. Sci. Technol. A 24, 995 (2006).