Near-field Scanning Optical Microscopy and Electron Microprobe Microscopy Investigations of Immiscibility Effects in Ind
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Near-field Scanning Optical Microscopy and Electron Microprobe Microscopy Investigations of Immiscibility Effects in Indium Gallium Phosphide Grown by Liquid Phase Epitaxy C. A. Paulson, A. B. Ellis Department of Chemistry, The University of Wisconsin, Madison, WI 53706 T. F. Kuech Department of Chemical Engineering, The University of Wisconsin, Madison, WI 53706 Abstract We have used Near-field Scanning Optical Microscopy (NSOM) and Electron Probe Microanalysis (EPMA) to study the topographic and microscopic optical properties of indium gallium phosphide (In1-xGaxP) samples grown by Liquid Phase Epitaxy (LPE) on gallium arsenide substrates. Photoluminescence (PL) intensity images gathered using NSOM exhibit strong, highly localized variations in the optical properties of these samples that are seen to occur roughly in registry with the surface topography. Shifts in the PL peak position (by 27 meV) occur across highly mismatched samples with high In content, whereas no shifts were seen for In1-xGaxP films with a nearly lattice matched composition. Compositional fluctuations lead to these PL peak energy shifts, measured by NSOM with a resolution of 250 nm. These composition fluctuations arise from the known solid-solid miscibility gap in the In1-xGaxP system at temperatures used for the growth of these samples. Introduction Indium gallium phosphide (In1-xGaxP) is an important alloy system that is used in many semiconductor electronic devices. Growth of In1-xGaxP is accomplished by a variety of methods, including Metal-Organic Vapor Phase Epitaxy (MOVPE) [1], Molecular Beam Epitaxy (MBE) [2], and Liquid Phase Epitaxy (LPE) [3]. Among these, LPE is recognized as having industrial appeal due to its high deposition rate. LPE deposition occurs under conditions that are close to thermodynamic equilibrium [3]. Under such conditions, immiscibility can be an important parameter for the LPE deposition of films [4]. Previous work has demonstrated that growth of an alloy composition within the thermodynamic miscibility gap can increase dislocation generation [5] and surface roughness [5], while decrease carrier mobility through alloy scattering [6]. Spatially-resolved investigations of immiscibility effects on LPE films have used Cathodoluminescence (CL) [7], Electron Microprobe Analysis (EPMA)[8], and Transmission Electron Microscopy (TEM) [8] among other techniques. Only a few studies report results on LPE films that have large mismatches to their substrates (∆a/a0 > 0.5%) [5][9][10]. We present results of Near-field Scanning Optical Microscopy (NSOM) investigations of LPE In1-xGaxP samples grown on gallium arsenide (GaAs) substrates over a range of lattice mismatch of 0 to 2%. The NSOM images reveal a high level of local variation in the photoluminescence (PL) for In1-xGaxP at compositions that are well removed from the lattice match condition of x = 51%. Since the NSOM experiment simultaneously determines surface topography, we also find that the PL fluctuations and the surface topography are correlated. Through comparison w
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