Photoluminescence Studies in CuAlS₂ Crystals

Abstract

Photoluminescence (PL) measurements have been carried out at low temperature (77 and 10 K) on CuAlS2 crystals grown by the chemical vapor transport method. Seven sharp PL lines have been observed near the band edge. Based on the photoreflectance measurements, the PL line at 3.550 eV has been assigned to a free exciton emission. The lines at 3.540, 3.532, 3.500 and 3.475 eV are tentatively assigned to the bound excitons, and they are discussed in terms of the crystal composition and the annealing conditions. This study also refers to the PL lines and peaks at about 2.9 eV.

Excitonic photoluminescence in CuAlS2 powders

“…Figure 2 shows the PL spectra in the range between 3.1 to 3.6 eV at temperatures from 15 to 295 K. Several sharp emission peaks were obtained at low temperatures. The emission peak of the 3.55 eV at 15 K may be due to a free exciton which corresponds to that reported in Shirakata et al [5]. The peak energy of a free-exciton measured at 15 K decreased with increasing temperature up to 295 K, reflecting the decrease of the energy gap.…”

“…Therefore, CuAlS 2 is expected to be a material for an ultraviolet emitter with a high emission efficiency at room temperature. However, it is not easy to induce the excitonic emission from CuAlS 2 because various types of defect caused by deviation from stoichiometric composition and/or impurities are easily formed in the crystal [4][5][6][7]. Only a few basic research of CuAlS 2 , which exhibited excitonic emission, were reported [2,5,8].…”

Chemistry of defect induced photoluminescence in chalcopyrites: The case of CuAlS2

“…4,5 The defect concentrations depend explicitly on the equilibrium Fermi energy, E F , through the defect formation energies and, in turn, E F depends on the concentration of the charged defects through the neutrality condition expressed in equation (14). Therefore, the values of the defects concentrations and E F are determined self consistently.…”

“…1 Among these Cu-III-VI 2 chalcopyrites CuAlS 2 has a 3.49 eV room temperature band gap, 2 and its bulk single crystals usually exhibit values of room-temperature p-type mobility and hole concentration of the order of 0.9 Scm −1 and 5.1×10 18 cm −3 respectively. 3 Photoluminescence (PL), high resolution photoreflectance (HPR) and time resolved photoluminescence (TR-PL) experiments reveal the existence of luminiscence emissions in CuAlS 2 at temperatures ranging from 10 K to 300 K. 4,5 It has been suggested that these emissions might be due to: a) free excitons (FE), b) donor and acceptor-bound emissions and c) donor-acceptor pair recombination (D + A − ) emissions. 4,5 (D + A − ) and donor-acceptor bound emissions are related to the intermediate optical band gap states that appear in defective CuAlS 2 and, therefore, PL emissions related with these excitons have wavelengths smaller than the optical band gap of CuAlS 2 .…”

“…3 Photoluminescence (PL), high resolution photoreflectance (HPR) and time resolved photoluminescence (TR-PL) experiments reveal the existence of luminiscence emissions in CuAlS 2 at temperatures ranging from 10 K to 300 K. 4,5 It has been suggested that these emissions might be due to: a) free excitons (FE), b) donor and acceptor-bound emissions and c) donor-acceptor pair recombination (D + A − ) emissions. 4,5 (D + A − ) and donor-acceptor bound emissions are related to the intermediate optical band gap states that appear in defective CuAlS 2 and, therefore, PL emissions related with these excitons have wavelengths smaller than the optical band gap of CuAlS 2 . In previous works, the orange PL emission observed in CuAlS 2 has been linked to a (D + A − ) transition.…”