Structural Defects in InSb Quantum Wells Grown on GaAs (001) Substrates via Al 0.09 In 0.91 Sb/GaSb-AlSb Strained Layer
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0891-EE01-11.1
Structural Defects in InSb Quantum Wells Grown on GaAs (001) Substrates via Al0.09In0.91Sb/GaSb-AlSb Strained Layer Superlattice/AlSb/GaSb Buffer Layers T.D. Mishima, M. Edirisooriya and M.B. Santos Homer L. Dodge Department of Physics and Astronomy, and Center for Semiconductor Physics in Nanostructures University of Oklahoma, Norman, OK 73019-2053, U.S.A. ABSTRACT Structural defects in InSb quantum well (QW) samples have been investigated by transmission electron microscopy (TEM). Using molecular beam epitaxy, an InSb QW with remotely-doped Al0.09In0.91Sb barriers was grown on a GaAs (001) substrate with buffer layers consisting of, in order from the substrate: 1 µm of GaSb, 1 µm of AlSb, 50 nm of GaSb-AlSb strained layer superlattice (SLS), and 3 µm of Al0.09In0.91Sb. Cross-sectional TEM analysis indicates that high densities of threading dislocations (TDs) are created at the two highly latticemismatched interfaces, the Al0.09In0.91Sb/GaSb-AlSb SLS and the GaSb/GaAs interfaces. Pairs of stereo images taken from plan-view TEM (PV-TEM) specimens show that TDs propagate through the InSb QW layer. The densities of TDs and micro-twin (MT) defects measured by PV-TEM are 9×108 /cm2 and 4×103 /cm, respectively. These values are worse than those in an InSb QW layer grown with a different buffer layer by a factor of ~4. The different buffer layer contains an InSb interlayer that effectively filters out both TDs and MTs. Adopting an interlayer structure and reducing the GaSb and AlSb layer thickness may make it possible to fabricate a lower-defect-density yet thinner InSb QW sample with the type of buffer layer examined in this study. INTRODUCTION Electrons in InSb have a high electron mobility, a large effective g factor and strong spinorbit effects [1]. Ongoing efforts are being made to develop InSb quantum well (QW) -based devices that take advantage of these properties, such as field effect transistors [2], mesoscopic magnetoresistors [3], ballistic transport devices [4] and spin transport devices. One key factor to improve the performance of such devices is the minimization of structural defects. Since there are no lattice-matched III-V substrates that are also semi-insulating, InSb QW structures are usually grown on semi-insulating GaAs (001) substrates in spite of the large lattice mismatch of 14.6% between InSb and GaAs. Efforts have been made to optimize the buffer layers for both InSb QW structures [5] and InSb epilayers [6-8] grown on GaAs (001). Recently, studies using transmission electron microscopy (TEM) and Hall effect measurements showed that the density of micro-twins (MTs) correlates with the electron mobility in the InSb QW layer [9-11]. When a MT passes through an InSb QW layer, it causes 1) an offset between the two parts of the QW bisected by the MT, 2) a different crystallographic orientation of the QW in the MT region, 3) bending in the QW near the MT and, 4) formation of a wall of aligned threading dislocations (TDs) which propagate along the MT [9-11].
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