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

Abstract

g-CuCl is a wide-band gap (E g ¼ 3:395 eV at 4 K), direct band gap, semiconductor material with a cubic zincblende lattice structure. A very large exciton binding energy (190 meV), assures efficient exciton-based emission at room temperature. Its lattice constant, a CuCl ¼ 0:541 nm means that the lattice mismatch to Si (a Si ¼ 0:543 nm) is o0.5%.g-CuCl on Si-the growth of a wide-band gap, direct band gap, optoelectronics material on silicon substrate is a novel material system, with compatibility to current Si-based electronic/optoelectronics technologies. Both n-type and p-type CuCl will be required for development of homojunction light-emitting diodes (LEDs). The authors report on the impact of incorporation of Zn for n-type doping of CuCl by co-evaporation of CuCl and ZnCl 2 .Polycrystalline Zn-doped g-CuCl thin films are grown on Si (1 1 1), Si (1 0 0), and glass substrates by physical vapour deposition. X-ray diffraction (XRD) studies confirm that this n-doped CuCl has a cubic zincblende structure with a preferred (1 1 1) orientation. Several excitonic bands are evident in low-temperature photoluminescence (PL) measurements such as the Z 3 free exciton at $388 nm; I 1 -bound exciton at $392 nm and M free biexciton at $393 nm. Cathodoluminescence (CL) and PL reveal a strong room temperature Z 3 excitonic emission at $385 nm. Electrical measurements indicate n-type conductivity with resistivity $34 Ocm. r

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

“…Similar to PL, the peak position is slightly red-shifted compared to the energy of ~3.23 eV measured for undoped CuCl. 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.…”

“…If contact noise is high, as in our case, a noise spike during just one of the eight Van der Pauw measurements can greatly affect the final result. Figure We have previously reported that doping of CuCl by co-evaporation with ZnCl 2 results in the quenching of the excitonic emission one day after deposition measured by UV-VIS spectroscopy and is accompanied by a decrease in the transmittance of the Zn-doped films [6]. For optoelectronic device applications both the electrical conductivity and the optical transmission should be as high as possible [9].…”

“…We have detected an approximately tenfold decrease in resistivity for the samples doped with a nominally 3 mole % ZnCl 2 compared to undoped CuCl. Details of the resistivity measurements can be found elsewhere [6]. Ohmic contacts to CuCl doped with a nominal 2-3 mole % Zn in the range of ±4V were achieved using Cu-Au co-evaporated metal contacts.…”

“…The CuCl, doped with ZnCl 2 , thin film samples with typical layer thicknesses of ~500 nm were grown on Si (111), Si (100) and glass substrates at room temperature using a basic physical vapour deposition method as previously described [6].…”

“…Several excitonic bands are evident in low temperature photoluminescence (PL) such as the Z 3 free exciton at ~3.20 eV; the I 1 bound exciton at ~3.18 eV and the M free biexciton at ~3.16 eV [6].…”