CHARACTERIZATION OF LOW-TEMPERATURE-GROWN ALSB AND GASB BUFFER LAYERS

The InGaSb/InAs strained layer superlattice (SLS) system has been prop osed theoretically to be a potentially useful long-wavelength infrared (IR) detector material by Mailhiot and Smith. These authors have sugg ested that GaSb substrates would be suitable for growth of these SLS. The benefit of InGaSb/InAs SLSs grown on GaSb(001) versus GaAs(001) su bstrates has been substantiated by a number of recent papers [J. L. Jo hnson, L. A. Samoska, A. C. Gossard, J. L. Merz, M. D. Jack, G. R. Cha pman, 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 In P, much less GaAs or Si. In particular, the poor quality of the GaSb s ubstrates leads to free carriers that make the samples electrically co nductive and absorb photons in the IR. Further studies of this materia ls system, therefore, require either improved GaSb substrates or a sui table 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 mat ched buffer layer for SLS growth GaSb and GaAs. The LTG layers were fo rmed by solid source molecular beam epitaxy using monomeric Sb from a cracker cell. The LTG-AlSb was grown at 450-500 degrees C while the Ga Sb layers were grown at 250-350 degrees C. Characterization of the lay ers by transmission electron microscopy (TEM), high-resolution x-ray d iffraction, atomic force microscopy, and Hall mobilities has been perf ormed. These results show that LTG GaSb on GaAs substrates are highly defective and become polycrystalline after about 1500 Angstrom of grow th. TEM analysis showed the formation of precipitates in LTG AlSb film s on GaSb after annealing. No Sb precipitates have been found in LTG G aSb. (C) 1997 American Vacuum Society.