Characterization of low-temperature grown AlSb and GaSb buffer layers

Abstract

The InGaSb/InAs strained layer superlattice (SLS) system has been proposed theoretically to be a potentially useful long-wavelength infrared (IR) detector material by Mailhiot and Smith. These authors have suggested that GaSb substrates would be suitable for growth of these SLS. The benefit of InGaSb/InAs SLSs grown on GaSb(001) versus GaAs(001) substrates has been substantiated by a number of recent papers [J. L. Johnson, L. A. Samoska, A. C. Gossard, J. L. Merz, M. D. Jack, G. R. Chapman, B. A. Baumgratz, K. Kosai, and S. M. Johnson, J. Appl. Phys. 80, 1116 (1996); T. D. Golding, H. D. Shih, J. T. Zborowski, W. C. Fan, C. C. Horton, P. C. Chow, B. C. Covington, A. Chi, J. M. Anthony, and H. F. Schaake, J. Vac. Sci. Technol. B 10, 880 (1992)]. Unfortunately, the current quality of GaSb substrates does not even match those of InP, much less GaAs or Si. In particular, the poor quality of the GaSb substrates leads to free carriers that make the samples electrically conductive and absorb photons in the IR. Further studies of this materials system, therefore, require either improved GaSb substrates or a suitable buffer layer to electrically isolate the substrate from the SLS. In this work, we explore the use of low-temperature grown (LTG) AlSb and GaSb, with and without annealing, as an effective near lattice matched buffer layer for SLS growth GaSb and GaAs. The LTG layers were formed by solid source molecular beam epitaxy using monomeric Sb from a cracker cell. The LTG-AlSb was grown at 450–500 °C while the GaSb layers were grown at 250–350 °C. Characterization of the layers by transmission electron microscopy (TEM), high-resolution x-ray diffraction, atomic force microscopy, and Hall mobilities has been performed. These results show that LTG GaSb on GaAs substrates are highly defective and become polycrystalline after about 1500 Å of growth. TEM analysis showed the formation of precipitates in LTG AlSb films on GaSb after annealing. No Sb precipitates have been found in LTG GaSb.