Low-temperature electron-paramagnetic-resonance study of extrinsic and intrinsic defects inCuGaSe2

Abstract

The low-temperature electron-paramagnetic resonance ͑EPR͒ of the compound semiconductor CuGaSe 2 was investigated. Spectra of as-grown lumps and powders with a defined maximum grain size were measured in X band. The spectra of two transition-metal impurities, Ni ϩ and Fe 2ϩ , could be identified and their appropriate EPR parameters are presented. The position of the Fermi-level energy within the forbidden zone as indicated by the occurrence of nickel and iron with these oxidation states is discussed by analogy with previous EPR investigations on other chalcopyrite semiconductors. An aging effect was observed, associated with the occurrence of EPR signals typical for Cu 2ϩ . The nature of the aging process is discussed with respect to the electronic properties of CuGaSe 2 for thin-film solar cell applications. ͓S0163-1829͑99͒01019-X͔

EPR g factors and tetragonal distortion for the isoelectronic Ni+ and Cu2+ centers in the CuGaSe2 crystal

“…The symmetry of this Cu 2 + center is rhombic and its spin-Hamiltonian parameters (g factors and hyperfine structure constants) were given. The observed hyperfine structure constants A x EA y and the small difference between the observed g x [E2.07 (1)] and g y [2.18 (2)] [10,11] suggest that the rhombic part of Cu 2 + center is very small. So the symmetry of Cu 2 + center can be regarded as approximately tetragonal [thus, g ?…”

“…and for Cu 2 + in CuGaSe 2 , g 99 4g ? [10,11]. Until now no theoretical studies have been made to explain this difference.…”

“…In addition, a typical Cu 2 + center was also found for the aged CuGaSe 2 powers [10,11]. The ageing process is significantly accelerated in water-saturated air of 100% humidity compared with dry air of 50% humidity, indicating an oxidation process from Cu + to Cu 2 + [10,11]. The symmetry of this Cu 2 + center is rhombic and its spin-Hamiltonian parameters (g factors and hyperfine structure constants) were given.…”

“…Electron paramagnetic resonance (EPR) technique is a powerful tool to study the defect model and defect structure for the paramagnetic defects in crystals [8,9]. The EPR measurements for the CuGaSe 2 crystal were made by Birkholz et al [10,11]. From the measurement, a Ni + ion at the Cu + site of CuGaSe 2 was observed and its EPR g factors g 99 and g ?…”

Electron spin resonance study of CuGa1−xMnxSe2 magnetic semiconducting compounds

“…However, the ESR as a probe for the properties of CuGaSe 2 to solar cell applications is not widely used. The first ESR study in CuGaSe 2 was reported by Birkholz and co-workers [6]. They have observed a pronounced ageing effect when the semiconducting material is contamined with Ni þ and Fe þ 2 ions.…”