X-Ray Characterization of Nanostructured Semiconductor Short-Period Superlattices
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X-Ray Characterization of Nanostructured Semiconductor Short-Period Superlattices Jianhua Li and S. C. Moss Physics Department, University of Houston, Houston, TX 77204-5005, U.S.A. V. Holy Institute of Condensed Matter Physics, Faculty of Science, Masaryk University, 61137 Brno, Czech Republic A.G. Norman and A. Mascarenhas National Renewable Energy Laboratory, Golden, CO 80401, U.S.A. J.L. Reno Sandia National Laboratories, Albuquerque, NM 87185, U.S.A. ABSTRACT Spontaneous lateral composition modulation during semiconductor thin film growth offers a particularly versatile and cost-effective approach to manufacture nanoscale devices. Recent experimental and theoretical studies have revealed that regular lateral composition modulation can be achieved via MBE growth of the so-called short-period superlattices and can be optimized via appropriate control of the global strain, substrate surface, and processing conditions. To characterize this phenomenon, we used synchrotron x-ray scattering to identify the interfacial morphology and laterally modulated composition profile of nearly strain-balanced InAs/AlAs short-period superlattices. Our results were compared with a theoretical model. It is shown that the lateral composition modulation is predominately caused by a vertically correlated morphlogical undulation of the superlattice layers. INTRODUCTION Over the past several years, a new approach for production of semiconductor nanostructures has emerged, which offers flexibility in controlling the electronic properties. With this approach, the production of 2D (quantum well), 1D (quantum wire), and 0D (quantum dot) nanostructures may be unified. The process is based on the growth of thin strained multilayer films and related short-period superlattices (SPS), which are by themselves 2D nanostructures ranging typically from one to several atomic layers. The small thickness of the SPS layers permits substantial selforganization of atoms at the interfaces, which leads to lateral composition modulation (LCM)[1, 2]. Depending on the dimensionality of this composition modulation, 1D or 0D structures with typical size of 10-40 nm can be achieved under proper control of the growth parameters. Nanoscale wire- and dot-like structures can be organized into regular arrays by properly controlling the long-range interaction of elastic fields between different compositional regions within the film (see Fig. 1), which would seem to be a formidable task for conventional surface selfassembly of islands. The possibilities of achieving such regular arrays of nanoscale structures have been demonstrated in (GaP)m/(InP)n [1], (InAs)m/(AlAs)n [2], and (InAs)m/(GaSb)n [3] SPS’s (m,n denote number of atomic mono-layers (ML)). Applications of these low-dimensional nano-materials cover optoelectronics (lasers, polarized light emitters and detectors), and highefficiency solar cells (using self-organized lateral multi-quantum-wells).
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Figure 1 Simulated wire (l.h.s. panel) and dot (r.h.s. panel) arrays arising from 1D and 2D latera
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