Excitation power and temperature dependence of excitons in CuInSe2

Abstract

Excitonic recombination processes in high quality CuInSe2 single crystals have been studied by photoluminescence (PL) and reflectance spectroscopy as a function of excitation powers and temperature. Excitation power dependent measurements confirm the identification of well-resolved A and B free excitons in the PL spectra and analysis of the temperature quenching of these lines provides values for activation energies. These are found to vary from sample to sample, with values of 12.5 and 18.4meV for the A and B excitons, respectively, in the one showing the highest quality spectra. Analysis of the temperature and power dependent PL spectra from the bound excitonic lines, labelled M1, M2, and M3 appearing in multiplets points to a likely assignment of the hole involved in each case. The M1 excitons appear to involve a conduction band electron and a hole from the B valence band hole. In contrast, an A valence band hole appears to be involved for the M2 and M3 excitons. In addition, the M1 exciton multiplet seems to be due to the radiative recombination of excitons bound to shallow hydrogenic defects, whereas the excitons involved in M2 and M3 are bound to more complex defects. In contrast to the M1 exciton multiplet, the excitonic lines of M2 and M3 saturate at high excitation powers suggesting that the concentration of the defects involved is low. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709448

Anisotropy of effective masses in CuInSe2

“…Very few reports have demonstrated resolved A and B free exciton (FX A , FX B ) lines in the photoluminescence (PL) spectra. 6,7 Only recently has the width of the excitonic features become sufficiently narrow to usefully apply magnetophotoluminescence (MPL). 8 The presence of a high degree of anisotropy for the hole effective mass was shown experimentally in uniaxial direct bandgap wurtzite semiconductors GaN.…”

A photoluminescence study of excitonic grade CuInSe2 single crystals irradiated with 6 MeV electrons

“…The M1 line, reported earlier as a multiplet with three 18 or four 20 components and assigned in Ref. 19 to interstitial copper atom (Cu i ) donors, appears in the PL spectrum in Fig.…”

“…The non-irradiated spectrum reveals peaks assigned to A ($1.0417 eV) and B ($1.0448 eV) free excitons. [17][18][19][20] The chalcopyrite crystal structure of CuInSe 2 can be derived from the sphalerite one of ZnSe by the ordered substitution of zinc with alternating indium and copper. Such a substitution results in a chalcopyrite structure with different lengths of the chemical bonds for the Cu-Se and In-Se pairs.…”

“…32) and CuInSe 2 . 20 Therefore, the determined activation energies should be compared with spectral distances to both the A and B free excitons.…”

“…8,16 However, there are relatively few reports revealing resolved excitonic features in the PL spectra from CuInSe 2 because of the challenges facing the growth of high-quality material. [17][18][19][20] This paper presents a study of the effects of 6 MeV electron radiation on high purity CuInSe 2 single crystals with a number of sharp excitonic features in the PL spectra. These features are used as sensitive indicators to monitor changes in the structural quality and defect balance of the material due to electron irradiation.…”