The use of wide-bandgap CuCl on silicon for ultra-violet photonics

Abstract

γ-CuCl is a wide-bandgap (E g = 3.395eV), direct bandgap, semiconductor material with a cubic zincblende lattice structure. Its lattice constant, a CuCl = 0.541 nm, means that the lattice mismatch to Si (a Si = 0.543 nm) is <0.5%. γ-CuCl on Si -the growth of a wide-bandgap, direct bandgap, optoelectronics material on silicon substrates is a novel material system, with compatibility to current Si based electronic/optoelectronics technologies. The authors report on early investigations consisting of the growth of polycrystalline, CuCl thin films on Si (100), Si (111), and quartz substrates by physical vapour deposition. X-ray diffraction (XRD) studies indicate that CuCl grows preferentially in the <111> direction. Photoluminescence (PL) and Cathodoluminescence (CL) reveal a strong room temperature Z 3 excitonic emission at ~387nm. A demonstration electroluminescent device (ELD) structure based on the deposition of CuCl on Si was developed. Preliminary electroluminescence measurements confirm UV light emission at wavelengths of ~380nm and ~387nm, due to excitonic behaviour. A further emission occurs in the bandgap region at ~360nm.

Characterisation of n-type γ-CuCl on Si for UV optoelectronic applications

“…A broad green emission band centred at ~2.39 eV is consistent with cathodoluminescence (CL) data performed on both undoped [14] and Zn-doped material [6]. Thickness dependent CL spectra have shown that the emission originates in the bulk of the CuCl film [15] and therefore may be related to grain boundaries. Three emissions occurring at energies greater than the CuCl bandgap at approximately 3.49eV, 3.70eV and 3.95eV, respectively are also detected.…”

Impact on structural, optical and electrical properties of CuCl by incorporation of Zn for n-type doping

“…Fourier transform infra-red (FTIR) and XRD analysis has shown this to be an effective means of sealing the undoped CuCl system for many months. We have previously shown that the excitonic emission of the UV/VIS spectrum of an undoped CuCl sample is maintained at the same intensity for at least 3 weeks by capping with liquid glass [15]. Testing the effectiveness of this system to seal the Zn-doped CuCl thin films is currently underway.…”

“…Over the past decade or so, research on the cuprous halides has focussed on three main areas: (1) Spectroscopic and theoretical studies of band structures and excitonic-based luminescence in CuCl, CuBr and copper halide-mixed crystals [5][6][7], (2) fundamental photoluminescence (PL) and spectroscopic studies of CuCl quantum dots embedded in NaCl crystals [8,9] and glass matrices [10,11], (3) surface studies of the growth mechanisms involved in the heteroepitaxy of CuCl single crystals on a number of substrates such as MgO (0 0 1) and CaF 2 (1 1 1) [12], reconstructed (0 0 0 1) haematite (a-Fe 2 O 3 ) [13] and both Si and GaAs [14]. We have previously demonstrated a simple electroluminescent device (ELD) structure based on the deposition of CuCl on Si [15]. Electroluminescence measurements confirm UV light emission at wavelengths of $380 and $387 nm due to excitonic behaviour.…”