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Cowley A.;Foy B.;Danilieuk D.;McNally P.;Bradley A.;McGlynn E.;Danilewsky A.
Physica Status Solidi (A) Applications and Materials
UV emission on a Si substrate: Optical and structural properties of γ-CuCl on Si grown using liquid phase epitaxy techniques
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Considerable 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 lat-tice mismatch-induced high dislocation densities for epitaxi-ally grown layers on non-native substrates. γ-CuCl is a direct bandgap material and an ionic wide bandgap I-VII semicon-ductor 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 prin-ciple, 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 al-kali halide flux compounds to depress the liquidus tempera-ture 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 compari-tively observed spectra for GaN or polycrystalline CuCl. This enhancement is believed to be caused by an interaction be-tween the KCl and CuCl material subsequent to the deposi-tion process, perhaps involving a reduction in Cl vacancy dis-tributions 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.
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