UV emission on a Si substrate: Optical and structural properties of γ‐CuCl on Si grown using liquid phase epitaxy techniques

Abstract

AbstractConsiderable research is being carried out in the area of wide band gap semiconductor materials for light emission in the 300–400 nm spectral range. Current materials being used for such devices are typically based on II–VI and III‐nitride compounds and variants thereof. However, one of the major obstacles to the successful fabrication of III‐N devices is lattice mismatch‐induced high dislocation densities for epitaxially grown layers on non‐native substrates. γ‐CuCl is a direct bandgap material and an ionic wide bandgap I–VII semiconductor with a room temperature free exciton binding energy of ∼190 meV (compared to ∼25 meV and ∼60 meV for GaN and ZnO, respectively) and has a band gap of 3.4 eV (λ ∼ 366 nm). The lattice constant of γ‐CuCl (0.541 nm) is closely matched to that of Si (0.543 nm). This could, in principle, lead to the development of optoelectronic systems based on CuCl grown on Si. Research towards this end has successfully yielded polycrystalline γ‐CuCl on Si(100) and Si(111) using vacuum‐based deposition techniques [1]. We report on developments towards achieving single crystal growth of CuCl from solution via Liquid Phase Epitaxy (LPE) based techniques. Work is being carried out using alkali halide flux compounds to depress the liquidus temperature of the CuCl below its solid phase wurtzite‐zincblende transition temperature (407 °C [2]) for solution based epitaxy on Si substrates. Initial results show that the resulting KCl flux‐driven deposition of CuCl onto the Si substrate has yielded superior photoluminescence (PL) and X‐ray excited optical luminescence (XEOL) behavior relative to comparitively observed spectra for GaN or polycrystalline CuCl. This enhancement is believed to be caused by an interaction between the KCl and CuCl material subsequent to the deposition process, perhaps involving a reduction in Cl vacancy distributions in CuCl. This paper presents a detailed discussion of a CuCl LPE growth system as well as the characterization of deposited materials using X‐ray diffraction (XRD), room temperature and low temperature PL, and XEOL. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)