High-resolution x-ray diffraction study of In 0.25 Ga 0.75 Sb/InAs superlattice
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High-resolution x-ray diffraction study of In0.25 Ga0.75 SbyyInAs superlattice A. Vigliante,a) H. Homma,b) J. T. Zborowski, T. D. Golding, and S. C. Moss Department of Physics, University of Houston, Houston, Texas 77204-5506 (Received 13 May 1998; accepted 16 December 1998)
An In0.25 Ga0.75 SbyInAs strained-layer superlattice, grown by molecular-beam epitaxy (MBE) on a GaSb[001] substrate, has been characterized by four-circle x-ray diffractometry. This system, proposed by Maliot and Smith for ir detection application, is challenging because of the two group V species and the likelihood of cross-incorporation of the different elements during growth, leading possibly to interdiffusion and thus, to a more diffuse interface. High-resolution x-ray diffraction (XRD) profiles were obtained about several reciprocal lattice points in order to extract a reliable set of structural parameters. The profiles were then successfully modeled by computer simulation. The presence of many sharp higher-order satellite reflections in the XRD profiles is a measure of the high quality of the superlattices. The normal and lateral structural coherence was also measured and will be discussed.
I. INTRODUCTION
In the last few decades the technology of III-V semiconductors has been increasingly developing for application in optoelectronic and high speed heterostructure devices. Heterojunctions, thin films, and superlattices (SL) have been grown artificially by depositing one atomic layer at a time. One important feature of the SL is the quantum size effect, which allows one to modify the energy levels and the band gap by appropriate choices of layer thicknesses. In 1982 Osbourn1,2 proposed for the first time to make use of the strain due to the lattice mismatch of different semiconductors to tailor the energy band gap, opening the door to the new field of strained-layer superlattices and valence band engineering. High quality lattice-mismatched SL will accommodate the elastic strain between the bilayers without generating dislocations, if the individual layer thickness doesn’t exceed the critical thickness value. The critical thickness depends on the competition balance between the strain energy associated with the degree of (uniform) layer stress and the incoherent interfacial energy, which forms when the layers adopt distinct (dislocation) interfaces. Its value has been theoretically and experimentally evaluated for several semiconductors. The (SL) Inx Ga12x SbyInAs has been proposed by Mailhiot and Smith3,4 as an alternative system to the IIVI Hg12x Cdx Te ternary alloy for infrared (ir) detection, due to the possibility of achieving a direct narrow band gap by tailoring the strain through changing the In concentration in Inx Ga12x SbyInAs. Figure 1 shows the
band gap alignment in the type II junction of InAsyInSb. Both the top of the valence band and the bottom of conduction band of InAs lie below the top of the valence band of GaSb. This system offers the significant advantage of decouplin
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