Magnetic field effect on free and bound excitons in chalcopyrite CuInS2

Abstract

The effect of a strong magnetic field (induction up to 10 T) on free and bound excitons in CuInS 2 single crystals is studied. A diamagnetic shift to higher energies is observed in the luminescence and reflectance spectra for free-exciton lines A LPB ≈ 1.5348 eV, A UPB ≈ 1.5361 eV, and BC ≈ 1.557 eV. The diamagnetic shifts of free-exciton lines A LPB , A UPB , and BC provide a basis for estimating the exciton reduced masses µ A LPB = 0.131m 0 , µ A UPB = 0.134m 0 , and µ BC = 0.111m 0 , respectively. Bound-exciton lines in luminescence spectra are split under the influence of the magnetic field. The magnitude of the Zeeman effect (g-factor of the magnetic splitting) is estimated.Introduction. The chalcopyrite semiconductor CuInS 2 has unique physical properties such as a high self-absorption coefficient α ≈ 10 5 cm -1 and a band gap E g ≈ 1.53 eV, which is a very good approximation to the maximum in the solar radiation spectrum [1]. This makes it very attractive to use CuInS 2 for fabrication of cheap and efficient solar cells [2][3][4]. However, only a limited number of publications on the study of the physical properties of structurally perfect CuInS 2 single crystals using classical optical methods, in particular, luminescence [1, 5-11] and reflectance [5,11], have appeared. More thorough studies of the nature of free and bound excitons, the exact value of the band gap, and the energy levels of intrinsic structure defects formed during growth of crystals or films are necessary to control the structural perfection, doping level, and recombination processes in this material (films, single crystals).It is well known that magneto-optical measurements are one of the reliable methods for studying exciton states and determining the nature of residual impurities and intrinsic structure defects in various semiconducting materials [12]. In our opinion, such information is critical for further improvement of the technology for fabricating highly efficient solar cells based on CuInS 2 chalcopyrites. Magneto-optical research was recently carried out only for CuGaS 2 [13,14] and CuInSe 2 [15] chalcopyrites. Similar research for CuInS 2 has not been reported because of the lack of high-quality single crystals, the optical spectra of which would exhibit rather narrow lines for free and bound excitons for observing magneto-optical effects.Herein the magneto-optical effect on free and bound excitons in structurally perfect CuInS 2 single crystals is studied for the first time using optical reflectance and photoluminescence (PL) under the influence of strong magnetic fields (up to 10 T) at 4.2 K.Experimental. High-quality CuInS 2 single crystals were grown by directed crystallization using a temperature gradient. The chemical composition of the elements in the crystals was determined by local x-ray spectral analysis on a Stereoscan 360 scanning electron microscope (Cambridge Instruments, UK) with an in-built AN100000 energy spectrometer (Link Analytical, UK) and by scanning Auger-electron spectroscopy on a PHI-660 spectrometer (...

Structural and optical properties of thin films of Cu(In,Ga)Se2 semiconductor compounds

“…The transmission spectra at low temperatures were recorded by direct immersion of the samples in the coolant, liquid nitrogen (~78 K), or liquid helium (4.2 K). Other features of the technique have been described elsewhere [9].…”

Photoluminescence of CuInS2 single crystals grown by traveling heater and chemical vapor transport methods

“…Spectra at 78 K were dominated by a line with a maximum at 1.537 eV and half-width ≈8 meV that was related to recombination of free A-excitons in the ground state (n = 1). The low-energy inflection near 1.532 eV on the path of the line for free excitons was related to line 2 of bound excitons according to the literature [8][9][10]. A weaker high-energy line separated by 15.7-16.2 meV from the line for free A-excitons was due to recombination of free A-excitons located in the first (n = 2) and second (n = 3) excited states.…”

“…1). Furthermore, some lines related to excitons 1, 2, 4, 5, 6, and 8, that were designated as before [8][9][10], were visible at 4.2 K in PL spectra (depending on the type of single crystal). It is noteworthy that some of these PL lines were previously observed [11][12][13][14].…”

Electrodeposited CuInS2Using Dodecylbenzene Sulphonic Acid As a Suspending Agent for Thin Film Solar Cell

“…CuInS 2 may be one of the most promising materials of ternary chalcopyrite semiconductors for photovoltaic applications due to the band gap energy of about 1.5 eV, which matches the solar spectrum for energy conversion and a large absorption coefficient. Furthermore, this material does not contain toxic elements in comparison with CuInSe 2 [1][2][3][4]. There are different methods for the preparation of CuInS 2 thin films, such as sputtering, chemical spray pyrolysis, chemical bath deposition, and electrochemical deposition [5][6][7][8].…”