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

Abstract

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 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)

Rb2CuX3 (X = Cl, Br): 1D All‐Inorganic Copper Halides with Ultrabright Blue Emission and Up‐Conversion Photoluminescence

“…It has been previously reported that γ‐CuX (X = Br and Cl) have significant light emission properties in the 300–400 nm spectral range, suitable for novel UV/blue light applications . Here, we also measured the room temperature emission spectra of γ‐CuX (Figure S14, Supporting Information), that show a UV‐blue light emission with the presence of two PL peaks at 384 and 395 nm for γ‐CuCl and at 422 and 433 nm for γ‐CuBr, in agreement with the previous reports 22a,23. However, the measured PLQY values of γ‐CuX are very low (<0.5%).…”

Cuprous halides semiconductors as a new means for highly efficient light-emitting diodes

“…It is observed that the optical gain and the luminescence of cuprous halides CuI/CuCl and CuBr/CuCl QWs would be much higher than those of III-V nitride layers or II-VI ZnO/MgZnO QWs due to the inherent strong excitonic effects and negligible electrostatic fields within the active layers. Our predictions agree with recent experimental results 39 qualitatively. Substantially high optical gain of I-VII cuprous halides QWs as compared with that of III-V nitride QWs or II-VI ZnO QWs and the cuprous halides semiconductor structure’s close lattice match to Si substrate are the clear manifestation of the possibility of highly efficient I-VII cuprous halides semiconductor based light-emitting devices for solid-state lighting and integrated optoelectronic components compatible to Si technology.…”

“…Recently, I-VII γ -cuprous halides semiconductors 20 such as CuCl, CuBr, and CuI have drawn attention 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 because these are zincblende direct band-gap semiconductors (3.3 eV for CuCl, 2.91 eV for CuBr and 2.95 eV for CuI) and have large exciton binding energies (190 meV for CuCl, 108 meV for CuBr and 58 meV for CuI) with their lattice constants closely matched to that of Si as can be seen by the table 1 . From this table, one can see that the lattice constant of Si, 0.543 nm, is very closely matched to that of CuCl, 0.542 nm.…”

“…Researches on the cuprous halides semiconductors have been focused on the following areas over the past decade: (1) spectroscopic and theoretical studies of band structures 26 27 28 29 30 31 32 33 , (2) photoluminescence studies of I-VII quantum dots embedded in NaCl crystals and glasses 22 24 25 33 , (3) surface studies of the growth mechanisms involved in the hetero epitaxy, and single crystal and poly crystal layer growth on Si and GaAs 23 35 36 37 38 39 40 . Especially, Nishida et al 23 demonstrated single crystal thin layera growth on GaAs and Si using ultra high vacuum (UHV) molecular beam epitaxy (MBE).…”

“…Especially, Nishida et al 23 demonstrated single crystal thin layera growth on GaAs and Si using ultra high vacuum (UHV) molecular beam epitaxy (MBE). As for a direct evidence of the exciton binding energy effects on the luminescence, it was observed that the luminescence of liquid phase epitaxy (LPE) grown polycrystalline CuCl on Si is considerably brighter (by 3 order of magnitude) than undoped single crystal GaN grown sapphire at room temperature 39 . An electroluminescence (EL) device employing polycrystalline γ -CuBr thin film active layer was also demonstrated 40 .…”