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Представлены результаты исследования спектров излучения кристаллов и тонких пленок CuInSe2 при непрерывном (2 Вт/см2) и наносекундном импульсном лазерном возбуждении в диапазоне плотности мощности возбуждения ~1–100 кВт/см2 и температурах 10–160 К. Обнаружено, что в кристаллах CuInSe2 стимулированное излучение возникает в спектральной области 1,033 эВ с минимальным уровнем пороговой накачки 9,8 кВт/см2, а при уровнях накачки 36–76 кВт/см2 наблюдается лазерное излучение. Установлено, что для тонких пленок CuInSe2, сформированных на стеклянных подложках с предварительно осажденным на стекло слоем молибдена (структура CuInSe2/Mo/стекло), характерно появление только стимулированного излучения в области энергий 1,014–1,097 эВ с минимальным уровнем пороговой накачки 30 кВт/см2 при температуре 10 К. Обсуждаются механизмы возникновения стимулированного и лазерного излучения в соединении CuInSe2.

The phase composition and structural and optical characteristics of thin films of Cu(In1–xGax)(SySe1–y)2 solid solutions with the chalcopyrite structure were investigated. The unit-cell constants according to x-ray diffraction analysis were a ~ 5.720 A and c ~ 11.52 A. The elemental compositions were x = Ga/(Ga + In) ~ 0.14 and y = S/(S + Se) ~ 0.11 for Cu(In1–xGax)(S ySe1–y)2 thin films. The optical band gap of Cu(In1–xGax)(S ySe1–y)2 solid solutions determined from measurements of photoluminescence spectra and luminescence excitation spectra at ~4.2 K was Eg ~ 1.122 eV. The mechanism of radiative recombination of nonequilibrium charge carriers in thin films of Cu(In1–xGax) (S ySe1–y)2 solid solutions is discussed.

Radiation-induced effects in Cu(In,Ga)Se2 alloy thin films after implantation with hydrogen ions with energies of 2.5, 5, and 10 keV and a dose of ~3 × 1015 cm–2 are studied. Comparative analysis of the optical characteristics of nonimplanted and hydrogen-implanted Cu(In,Ga)Se2 films is conducted on the basis of photoluminescence spectra and luminescence-excitation spectra recorded at liquid-helium temperature (~4.2 K). The band gap determined for Cu(In,Ga)Se2 alloys by mathematical processing of the luminescence-excitation spectra is ~1.171 eV. In the photoluminescence spectra of nonimplanted and hydrogen-implanted Cu(In,Ga)Se2 films, an intense band is detected, with a maximum at ~1.089 eV. The band is defined by the recombination of free electrons with holes localized in the valence-band tails. It is established that broad bands with maximums at the energies 0.92 and ~0.77 eV are defined by the radiative recombination of nonequilibrium charge carriers at deep energy levels of ion-induced acceptor defects formed in the band gap of Cu(In,Ga)Se2 alloys. The conditions for the effect of the ion passivation of dangling electron bonds at the surface and in the bulk of polycrystalline Cu(In,Ga)Se2 films and the nature of structural point defects and the mechanisms of radiative recombination are discussed.

The emission spectra of thin nanocrystalline films of Cu(In1 – xGax)(SySe1 – y)2 (CIGSSe) direct-gap solid solutions in the structure of solar cells, recorded upon continuous-wave laser excitation (~0.5 W/cm2) and nanosecond pulsed laser excitation with a power density in the range of 0.1–53 kW/cm2 at temperatures ranging from 10 to 300 K, are analyzed. It is found that stimulated emission (SE) occurs in thin CIGSSe films at temperatures from 10 to 90 K in the spectral range hν = 1.062–1.081 eV, with a minimum threshold-pump level of ~1 kW/cm2. It is shown that the spontaneous emission band is blue-shifted with an increase in the excitation intensity. It is also established that, with an increase in temperature, the photoluminescence (PL) band (upon weak excitation) and the stimulated-emission band are blue-shifted, whereas the PL band is red-shifted upon strong excitation. The possible reasons and mechanisms for the influence of temperature and excitation intensity on the spectral positions of the spontaneous and stimulated emission bands for the solid-solution films are discussed.

Plasmonic enhancement of the photoluminescence in hybrid structures with SiGe quantum dots and Ag nanoislands was found. Ag nanoislands grown on the top of the multilayer structures with SiGe quantum dots (QDs) support a surface plasmon resonance that can be tuned to the QD emission wavelength by changing of Ag nanoparticle parameters. Photoluminescence measurements of the hybrid metal-semiconductor nanostructures revealed a fourfold increase of the integral intensity of SiGe QD emission in the spectral range from 0.8 to 1 eV.

Excitonic quality CuInSe2 crystals were studied using low-temperature (10 K) photoluminescence (PL) excited by continuous wave and nanosecond pulsed lasers at power densities from 0.01 to 76 kW/cm2. Increasing the excitation power density level to 26 kW/cm2 resulted in the appearance of a stimulated emission SE-band in the PL spectra at 1.035 eV. Further increase in the excitation level to 39 kW/cm2 generated on the top of the SE band, a structure of equidistant sharp lines attributed to laser emission. © 2021 Author(s). This work was supported by State Program of Scientific Research of the Republic of Belarus “Physical Material Science, New Materials and Technologies” (Project No. 1.4.4) and Belarusian Republican Foundation of Basic Research (Grant No. F20M-058). The research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (“Spin” No. AAAA-A18-118020290104-2).

© 2020, Springer Science+Business Media, LLC, part of Springer Nature.The Cu2SnS3 (CTS) thin films were produced by deposition of Sn/Cu layers by RF sputtering followed by annealing in an Ar/S atmosphere with S and Sn sources. According to XRD analysis and Raman spectroscopy, it was shown that single-phase CTS films of a monoclinic structure with traces of the CuxS phase were formed at a temperature of 520°C. Scanning electron microscopy revealed a compact and homogeneous microstructure of the polycrystalline CTS layers. Photoluminescence spectra of the СTS films of monoclinic modification show one wide peak in the energy range of 0.7–1.0 eV, due to optical transitions of electrons from the conduction band to deep energy levels of acceptor-type defects.

Thin films of Cu(In,Ga)Se2 on Mo coated glass substrates were studied by photoluminescence (PL) technique before and after irradiation in liquid nitrogen bath with a dose of 1.8 x 1015 cm−2 of 10 MeV electrons to determine the nature of radiation defects in Cu(In,Ga)Se2. The PL spectra before irradiation contain a broad dominant band at 1 eV, consisting of 3 peaks P1, P2 and P3, and two low intensity bands P4 at 0.86 eV and P5 at 0.77 eV. Because of their strong j-shift the P1, P2 and P3 were assigned to the free-to-bound (FB) recombination of free electrons and holes localised at 3 different acceptors whose energy levels are affected by potential fluctuations of the valence band. The P4 and P5 bands were also assigned to the FB recombinations of free electrons but with deeper acceptors. Irradiation reduced the PL intensity of the dominant 3 bands P1, P2 and P3. We assign such a reduction to the formation of nonradiative defects acting as deep traps. Irradiation did not change the j-shift of the P3 band (12 meV/d) suggesting that the acceptor, associated with P3, was not affected by irradiation. However, irradiation reduced the P2 j-shift from 13.8 meV/d to 4 meV/d demonstrating a significant reduction of the compensation level associated with this acceptor. Warming to the room temperature doubled the intensity of the dominant band probably due to annealing of some radiation induced defects. It increased the P2 j-shift to 10 meV/d demonstrating rising compensation level associated with this acceptor.

Thin films of Cu2ZnSnSe4 (CZTSe) were fabricated by the selenisation of metallic precursors sequentially deposited on Mo coated glass substrates. The surface morphology and cross section, studied by a scanning electron microscope (SEM), reveal densely packed grains with sizes in excess of 1 µm and CZTSe film with a thickness of 1.4 µm. The elemental composition of both the precursors and CZTSe films was measured by an energy dispersive X-ray analyser demonstrated a copper deficiency and zinc excess as well as a near stoichiometric content of Se. A set of 4 as deposited CZTSe films was used to produce solar cells with the structure ZnO/CdS/Cu2ZnSnSe4/Mo/glass. These films were coated with CdS buffer layer using a standard chemical bath deposition after chemical etching using KCN or/and ammonia: film E was not etched, film B was etched in KCN for 2 minutes, film C was etched in KCN for 5 minutes and film D was etched in KCN for 30s and then in ammonia for 5 minutes. Solar cells were then completed by DC-magnetron deposition of ZnO/ZnO:Al transparent front contacts. Finally solar cells with areas of 3x3 mm2 were separated by mechanical scribing. The structural properties of the cells and phase content of the CZTSe layer were examined by x-ray diffraction (XRD). Low intensity reflexes of the secondary phases SnSe and SnSe2 were also present. The bandgaps Eg of the CZTSe layers in the cells, measured by photoluminescence excitation (PLE) at 4.2 K, were found to be of 1.05 eV in all the four cells. This cell also showed the highest FF of 41.1% whereas the best Isc of 46.6 mA/cm2, demonstrated by the D cell. The highest conversion efficiency of 6.2% was obtained for the E cell, produced without any etch, and for the D one after 30 s etch in KCN plus 5 minutes in ammonia.

The stimulated emission of Cu(In,Ga)Se2 alloy thin films formed by magnetron-assisted sputtering onto a sodium-fluoride layer deposited onto a molybdenum layer on a glass substrate is observed. The structural and optical parameters of the films are determined by scanning electron microscopy, local X-ray spectral microanalysis, X-ray structural analysis, and low-temperature luminescence (T = 10 K) measurements in the range of excitation levels of 1.6–75 kW cm–2 provided by nanosecond nitrogen-laser pulses. The stimulated emission threshold corresponds to ~25 kW cm–2. Comparative analysis of the emission of Cu(In,Ga)Se2 thin films suggests that the introduction of sodium results in significant improvement of the structural quality, specifically, in a decrease in the density of energy states in the band tails and in a decrease in the concentration of nonradiative-recombination centers.

The photoluminescence (PL) of Ge/Si nanostructures synthesized by using Ge + ion bombardment is studied. The structure represents a Si substrate with GeSi nanoclusters created by 80 keV Ge implantation with a fluence of ∼1015 ions/cm 2 and subsequent thermal annealing. The PL measurements confirm the advantage of Ge/Si structures synthesized using Ge + ion bombardment over the usual epitaxial structures with GeSi quantum dots. The presence of defects produced by Ge implantation results in pronounced PL at telecom wavelengths up to room temperature. The results provide a basis for creating efficient light emitters compatible with the existing Si technology.

A comparative analysis of free and bound excitons in the photoluminescence (PL) spectra of CuInS2 single crystals grown by the traveling heater (THM) and the chemical vapor transport (CVT) methods is presented. The values of the binding energy of the A free exciton (18.5 and 19.7 meV), determined by measurements of the spectral positions of the ground and excited states, allowed the Bohr radii (3.8 and 3.7 nm), bandgaps (1.5536 and 1.5548 eV) and dielectric constants (10.2 and 9.9) to be calculated for CuInS2 crystals grown by THM and CVT, respectively. © 2017 Elsevier B.V.

Glasses of the K2O ZnO Al2O3 SiO2 system co-doped with Eu2O3 and Yb2O3 were prepared by the melt-quenching technique. Transparent zincite (ZnO) glass–ceramics were obtained by secondary heat-treatments at 680–860 °C. At 860 °C, traces of Eu oxyapatite appeared in addition to ZnO nanocrystals. The average crystal size obtained from the X-ray diffraction data was found to range between 14 and 35 nm. Absorption spectra of the initial glasses are composed of an absorption edge and absorption bands due to electronic transitions of Eu3+ ions. With heat-treatment, the absorption edge pronouncedly shifts to the visible spectral range. The luminescence properties of the glass and glass-ceramics were studied by measuring their excitation and emission spectra at 300, 78, and 4.2 K. Strong red emission of Eu3+ ions dominated by the 5D0–7F2 (612 nm) electric dipole transition was detected. Changes in the luminescence properties of the Eu3+-related excitation and emission bands were observed after heat-treatments at 680 °C and 860 °C. The ZnO nanocrystals showed both broad luminescence (400–850 nm) and free-exciton emission near 3.3 eV at room temperature. The upconversion luminescence spectrum of the initial glass was obtained under excitation of the 976 nm laser source.

The photoluminescence (PL) of the combined Ge/Si structures representing a combination of large (200–250 nm) GeSi disk-like quantum dots (nanodisks) and four-layered stacks of compact groups of smaller (30 nm) quantum dots grown in the strain field of nanodisks was studied. The multiple increase in the PL intensity was achieved by the variation of parameters of vertically aligned quantum dot groups. The experimental results were analyzed on the basis of calculations of energy spectra, electron and hole wave functions. It was found that the quantum dot arrangement in compact groups provides the effective electron localization in Δx,y-valleys with an almost equal probability of finding an electron in the Si spacer and Ge barrier. As a result, the main channels of radiative recombination in the structures under study correspond to spatially direct optical transitions.

The effect of solar cell processing (including etching in KCN along with deposition of CdS and ZnO) on photoluminescence (PL) spectra and bandgap E g (measured at 4.2 K by photoluminescence excitation) of Cu 2 ZnSnSe 4 films, produced by selenising metallic precursors at 450 °C, 500 °C and 550 °C, was studied. Temperature and excitation intensity analysis of the P1 dominant band in the PL spectra of solar cells suggests that after processing this band still can be assigned to the free-to-bound recombination of free electrons with holes bound at deep acceptor levels influenced by valence band-tails. However processing increased the intensity of P1 and blue shifted it. The strongest effect was observed for the film selenised at 500 °C. For the film selenised at 450 °C the blue shift and increase in the intensity were smaller and only a slight intensity rise was found for the film selenised at 550 °C. The intensity increase we assign to a reduction in the concentration of non-radiative recombination centers on the surface because of the etching and changes in doping due to inter-diffusion of Cd, S, Se and Zn after the deposition of CdS. Such an inter-diffusion depends on the elemental composition of the films defining the chemistry of defects and influencing E g which increased in the film selenised at 500 °C but decreased in the other films. Processing increased the P1 shift rate (j-shift) with excitation power change in all the films demonstrating a higher compensation degree in the solar cells which is consistent with the formation of an interface layer containing new donors Cd Cu . © 2019 Elsevier B.V.

Cu2ZnSnSe4 (CZTSe) is one of the leading candidates for the absorber layer in sustainable solar cells. Thin films of CZTSe with a near stoichiometric [Cu]/[Zn + Sn] were used to produce solar cells with conversion efficiency η = 6.4% by a standard solar cell processing including KCN etching and the deposition of CdS and ZnO. Both CZTSe films and solar cells were examined using photoluminescence (PL) to analyse the nature of radiative recombination and photoluminescence excitation (PLE) at 4.2 K to determine the bandgap (E g). Low temperature PL spectra of the films reveal an intense band P1 at 0.81 eV and a low intensity band P2 at 0.93 eV. Their temperature and excitation intensity dependencies suggest that they both involve recombinations of free electrons with holes localised at acceptors with the energy level influenced by potential fluctuations in the valence band. We associate P1 and P2 with different fractions of CZTSe: with a lower and higher degree of order of Cu and Zn on the cation sub-lattice, respectively. Device processing reduced the intensity of P1 by 2.5 whereas the intensity of P2 increased by a 1.5. We assign this to a low temperature annealing due to CdS and ZnO deposition which increased the fraction of CZTSe with high degree of Cu/Zn order and decreased the fraction with low degree of Cu/Zn order. Device processing increased E g, blue shifted P1, decreased its width, j-shift and the mean depth of potential fluctuations. These can also be related to the annealing and/or KCN etching and the chemical effect of Cd, due to CdS replacing copper at the CdS-CZTSe interface layer. Processing induced a new broad band P3 at 1.3 eV (quenching with E a = 200 meV) which we attributed to defects in the CdS layer. © 2018 IOP Publishing Ltd.

Hybrid structures containing Ag nanoparticles and GeSi quantum dots were developed using the self-organization of metal nanoislands on the surface of a strained semiconductor structure. The enhanced photoluminescence from GeSi quantum dots (QDs) coupled with Ag nanoislands was obtained. Ag nanoislands epitaxially grown on top of the multilayered structures with GeSi QDs support a surface plasmon resonance that can be tuned to the QD emission wavelength by changing Ag nanoparticle parameters. The numerical modeling of surface plasmon resonance allows attributing this effect to the increase of the recombination rate due to the coupling of QD emitters with Ag nanoislands.

Cu2ZnSnSe4 (CZTSe) is a semiconductor used as the absorber layer in highly promising sustainable thin film solar cells. The authors study the effect of Ar+ etching of copper deficient and zinc excess CZTSe thin films deposited on Mo/glass substrates on the surface elemental composition, measured by x-ray photoelectron spectroscopy, and photoluminescence (PL) spectra. Low temperature PL spectra reveal a broad asymmetrical band at 0.95 eV. The temperature and excitation intensity dependencies of this band suggest that it is a free-to-bound (FB) recombination of electrons from the conduction band with holes localized at an acceptor affected by potential fluctuations. The surface composition of the as grown films demonstrates a strong copper deficiency: [Cu]/[Zn + Sn] = 0.33. The etching of the film surface using Ar+ beam increases [Cu]/[Zn + Sn] to 0.51, which is significantly smaller than that of 0.78 in the bulk, measured by wavelength dispersive x-ray analysis, demonstrating the presence on the surface of a copper-depleted layer. The Ar+ etching drastically reduces the FB band intensity by a factor of 4.5, broadens it and develops a low energy tail. Ar ions displace atoms in CZTSe lattice creating primary radiation defects, vacancies, and interstitials, which recombine at room temperature forming antisite defects with deep energy levels. Some of them generate the observed low energy tail and increase the mean depth of potential fluctuation γ, determined from the shape of the low energy side of FB band, from 24 meV before Ar+ etching to 35 meV after. Other deep defects work as nonradiative recombination centers reducing the intensity of the FB band. © 2018 Author(s).

Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se2 thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se2 thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm2. It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se2 thin films. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

We present an optical spectroscopy study of Cu2ZnSnSe4 (CZTSe) thin films deposited on Mo/glass substrates. The [Cu]/[Zn+Sn] ratio in these films varies from nearly stoichiometric to strongly Cu deficient and Zn rich. Increasing Cu deficiency and Zn excess widens the bandgap Egdetermined using photoluminescence excitation (PLE) at 4.2 K, from 0.99 eV to 1.03 eV and blue shifts the dominant band in the photoluminescence (PL) spectra from 0.83 eV to 0.95 eV. The PL spectra of the near stoichiometric film reveal two bands: a dominant band centred at 0.83 eV and a lower intensity one at 0.93 eV. The temperature and excitation intensity dependence of the PL spectra help to identify the recombination mechanisms of the observed emission bands as free-to-bound: recombination of free electrons with holes localised at acceptors affected by randomly distributed potential fluctuations. Both the mean depth of such fluctuations, determined by analysing the shape of the dominant bands, and the broadening energy, estimated from the PLE spectra, become smaller with increasing Cu deficiency and Zn excess which also widens Eg due to an improved ordering of the Cu/Zn atoms. These changes in the elemental composition induce a significant blue shift of the PL bands exceeding the Eg widening. This is attributed to a change of the dominant acceptor for a shallow one, and is beneficial for the solar cell performance. Film regions with a higher degree of Cu/Zn ordering are present in the near stoichiometric film generating the second PL band at 0.93 eV. © 2017

The irradiation-induced effects in Cu(In,Ca)Se2 thin films after irradiation with hydrogen ions with dose of [Formula: see text][Formula: see text]cm[Formula: see text] and different energies in the range of 2.5–10[Formula: see text]keV were studied. Irradiated and nonirradiated thin films were investigated by low-temperature (4.2[Formula: see text]K) photoluminescence and photoluminescence excitation methods. The appearance of intense bands at [Formula: see text][Formula: see text]eV and 0.77[Formula: see text]eV in the photoluminescence spectra may be related to radiative recombination on the irradiation-induced defects with deep energy levels in the bandgap of Cu(In,Ca)Se2 solid solutions. A possible nature of these defects and process of radiative recombination are discussed.

The bandgaps of 1.187[Formula: see text]eV in non-irradiated nanostructured thin films of Cu(In,Ga)Se2 (CIGSe) and of 1.182[Formula: see text]eV in those films irradiated with 10[Formula: see text]keV hydrogen ions were determined using optical transmission and reflection spectroscopy at 4.2[Formula: see text]K. The observed reduction in the bandgap is assigned to the formation of secondary antisite defect complexes inducing band tails of the density of states in the valence band.

We present structural and optical spectroscopy studies of thin films of Cu2ZnSnSe4 (CZTSe) with strong copper deficiency deposited on Mo/Glass substrates and selenised at 450, 500 or 550°C. Solar cells fabricated from these films demonstrated efficiencies up to 7.4% for selenisation at 500°C. Structural analysis based on X-ray diffraction and Raman spectroscopy revealed the presence of SnSe2 in the film selenised at 450°C but not in the films selenised at higher temperatures. A progressive decrease of the Sn and Se content was observed as the selenisation temperature increased. Photoluminescence excitation was used to determine the bandgaps at 4.2 K. Detailed measurements of the temperature and excitation intensity dependencies of the photoluminescence spectra allow the recombination mechanisms of the observed emission bands to be identified as band-to-impurity and band-to-band transitions, and their evolution with selenisation temperature changes to be analysed. The strongest band-to-band transition is recorded in the PL spectra of the film selenised at 500°C and can be observed from 6 K to room temperature. The compositional and structural changes in the films and their influence on the optoelectronic properties of CZTSe and solar cells are discussed. © 2016 Elsevier B.V. All rights reserved.

Photoluminescence properties of highly strained Ge/Si multi-layer heterostructures with incorporated groups of laterally ordered SiGe quantum dots are studied in the wide range of temperatures from 4.2 to 300 K. The phononless radiative recombination mechanism in the groups is found to be dominating. A photoluminescence signal from SiGe quantum dots is observed up to 300 K. The activation energy ( ≈ 211 meV) of photoluminescence thermal quenching can be associated with transition of holes from the laterally ordered quantum dots to the valence band states in the Ge wetting layer.

High-quality single crystals of CuInSe2 with near-stoichiometric elemental compositions were irradiated with 6 MeV electrons, at doses from 1015 to 3 × 1018 cm−2, and studied using photoluminescence (PL) at temperatures from 4.2 to 300 K. Before irradiation, the photoluminescence spectra reveal a number of sharp and well resolved lines associated with free- and bound-excitons. The spectra also show broader bands relating to free-to-bound transitions and their phonon replicas in the lower energy region below 1.0 eV. The irradiation with 6 MeV electrons reduces the intensity of the free- and the majority of the bound-exciton peaks. Such a reduction can be seen for doses above 1016 cm−2. The irradiation induces new PL lines at 1.0215 eV and 0.9909 eV and also enhances the intensity of the lines at 1.0325 and 1.0102 eV present in the photoluminescence spectra before the irradiation. Two broad bands at 0.902 and 0.972 eV, respectively, are tentatively associated with two acceptor-type defects: namely, interstitial selenium (Sei) and copper on indium site (Cu In). After irradiation, these become more intense suggesting an increase in the concentration of these defects due to irradiation.