Anisotropy in Atomic-Scale Interface Structure and Mobility in Inas/Ga 1 _ X in x sb Superlattices
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(io0) cross-sectional planes of the superlattice indicates that interfaces in the (110) plane
exhibit a higher degree of interface roughness than those in the (110) plane, and that the Gal-xln 5Sb-on-InAs interfaces are rougher than the InAs-on-Gal,_InxSb interfaces. The roughness data are consistent with anisotropy in interface structure arising from anisotropic island formation during growth, and in addition with a growth-sequence-dependent interface asymmetry resulting from differences in interfacial bond structure between the superlattice layers. Roughness data are compared with measurements of anisotropy in low-temperature Hall mobilities of the samples. INTRODUCTION InAs/Ga,-_InSb strained-layer superlattices have shown great promise for application in mid-to-long wavelength infrared imaging applications.'-4 However, the atomic-scale interfacial properties of the superlattice structures have been found to be of crucial importance in determining material and device properties. Because both Group III and Group V constituents change from one superlattice layer to the next, two distinct bond configurations - InSb-like and Ga,-_xInAs-like - can be present at each interface. Ga-x 6 Sb/InAs superlattices grown with 5 rn InSb-like interfacial bonds have been demonstrated to possess superior device characteristics compared to those grown with Ga,6 1n•,As-like bonds.', 6 Previous studies provided evidence of atomic-scale interface roughness and asymmetry in InAs/GaSb7-'° and InAs/Ga,-_InxSb" superlattices. A detailed understanding of the atomic-scale structural and compositional properties of these interfaces is therefore essential to the optimization of electrical and optical properties of device structures based on the InAs/GallnxSb and related material systems. In this paper we describe a detailed, quantitative analysis of interface structure in InAs/Ga,,InxSb superlattices using cross-sectional scanning tunneling microscopy (STM). STM data are used to investigate directly and quantitatively the degree of directional anisotropy and growth-sequence dependence in interface structure. To quantify the interface structure observed by STM, individual interface profiles are extracted from the images and their roughness spectra calculated. The roughness spectra show that interfaces in the (io0) plane of the superlattice exhibit larger roughness amplitudes and correlation lengths than interfaces in the (110) plane, and that interfaces in which GalxIn 6Sb has been grown on InAs exhibit larger roughness amplitudes and correlation lengths than interfaces in which InAs has been grown on Ga,-x1n6Sb. 147
Mat. Res. Soc. Symp. Proc. Vol. 448 0 1997 Materials Research Society
We attribute these features in interface structure to anisotropy in island formation during sample growth, and to a dependence on growth sequence of bond configurations at the interfaces. Results obtained from STM studies are also compared with low-temperature Hall mobility studies of similar structures grown on GaAs substrates. EXPERIMENT The InAs/Ga1 xlnxS
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