Sharp Optical Emission from CuInSe₂ Thin Films Grown by Molecular Beam Epitaxy

Abstract

Optical properties of CuInSe2 (CIS) films grown on (001) GaAs by molecular beam epitaxy (MBE) have been investigated by means of low temperature photoluminescence (PL) spectroscopy. Distinct emission lines including a bandedge emission were observed reproducibly from Cu-rich films, indicating high crystalline quality. Such well-defined PL spectra have made possible the extensive characterization of radiative recombination processes through the intrinsic defects in this material; some of the emission lines were attributed to phonon replicas with a phonon energy of 28–29 meV for the first time. PL spectra were found to be very sensitive to the MBE growth parameters such as substrate temperature, suggesting dominant defects in CIS epitaxial films can be controlled by varying the growth conditions.

Characterization of CuIn(Ga)Se2 Thin Films

“…2c. It is worth mentioning that the spectral shape and energy positions of the recombinations is almost identical to those observed in Cu-rich layers grown by molecular beam epitaxy (MBE) [4].…”

“…Recombinations with energy positions, lineshape and phonon-structure almost identical to the recombinations I and II a are well known in Cu-rich CuInSe 2 without Ga [4]. Recombination III was not reported so far.…”

“…One highly conductive Cu 2± ±x Se phase does not contribute to the photoluminescence (PL), the PL is caused by CuInSe 2 and CuIn 1± ±x Ga x Se 2 phases. The two well known recombinations with zero-phonon lines (ZPL) at 0.96 and 0.90 eV originate from CuInSe 2 crystallites [4], while a broad energetically higher lying luminescence band arises from crystallites containing CuIn 1± ±x Ga x Se 2 phases. The properties of the 0.96 and the 0.90 eV luminescence bands are very well described within the donor±acceptor pair (DAP) recombination model developed by Thomas and Hopfield [5] in the sixties.…”

Photoluminescence and Photoluminescence Excitation Spectroscopy of Cu(In,Ga)Se2Thin Films

“…PL has been performed on CIGS epitaxial layers [5][6][7], polycrystals [8] and bulk single crystals [9][10]. Only a few studies have incorporated photoluminescence excitation spectroscopy (PLE), with mixed results [6,11].…”

Influence of Flash Lamp Annealing on the Optical Properties of CIGS Layer

“…Figure 2a shows the room-temperature photoluminescence spectra obtained from virgin and ash lamp annealed samples. The PL spectrum of the virgin sample consists of broad band with a maximum intensity located at 1210 nm due to near-band-edge emission and free-to--bound (FB) transition at about 1250 nm [21,22]. The ash lamp annealing leads to an enhancement of the maximum NBE-PL intensity and shifts its position of about 10 nm to the longer wavelength (smaller band gap) and the separation between the two observed emissions (NBE and FB) is clearly visible.…”