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Semiconductor Cu2ZnSn(S x Se1-x )4 (CZTSSe) solid solution is considered as a perspective absorber material for solar cells. However, during its synthesis or deposition, any modification in the resulting optical properties is hardly predicted. In this study, experimental and theoretical analyses of CZTSSe bulk crystals and thin films are presented based on Raman scattering and absorption spectroscopies together with compositional and morphological characterizations. CZTSSe bulk and thin films are studied upon a change in the x = S/(S + Se) aspect ratio. The morphological study is focused on surface visualization of the solid solutions, depending on x variation. It has been discovered for the first time that the surface of the bulk CZTSSe crystal with x = 0.35 has pyramid-like structures. The information obtained from the elemental analysis helps to consider the formation of a set of possible intrinsic lattice defects, including vacancies, self-interstitials, antisites, and defect complexes. Due to these results and the experimentally obtained values of the band gap within 1.0-1.37 eV, a deviation from the calculated band gap values is estimated in the range of 1.0-1.5 eV. It is suggested which defects can have an influence on such a band gap change. Also, on comparing the experimental Raman spectra of CZTSSe with the theoretical modeling results, an excellent agreement is obtained for the main Raman bands. The proposed theoretical approach allows to estimate the values of concentration of atoms (S or Se) for CZTSSe solid solution directly from the experimental Raman spectra. Thus, the visualization of morphology and the proposed theoretical approach at various x values will help for a deeper understanding of the CZTSSe structure to develop next-generation solar cells.

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.

This work devotes to a comparative study of the photoluminescence of Ge/Si epitaxial structures with quantum dots created with using ion beam irradiation and structures with Ge nanoclusters formed as a result of the implantation of Ge ions into silicon and subsequent annealing.

A multiple enhancement of the photoluminescence (PL) of Ge/Si quantum dots (QDs) in structures with silver nanoparticles was obtained. The amplification effect is explained by an increase in the rate of radiative recombination of charge carriers localized at QDs.

High structural quality single crystals of CuGaSe2 were studied using photoluminescence (PL), optical reflectivity (OR) and circularly polarised magneto-reflectance (MR) at 4.2 K in magnetic fields B up to 14 T. At B = 0 T both the PL and OR spectra exhibited the A free exciton, associated with the uppermost sub-band of the valence band of CuGaSe2 split by the tetragonal distortion in the lattice. The magnetic field induced a blue shift of the exciton in the MR spectra. Analysis of the dependence of the spectral position of the A exciton on B in the MR spectra, measured for both right and left circular polarisations of light, enabled the magnitude of its effective g-factor to be determined |g| = 0.46. © 2020 IOP Publishing Ltd.

In the present work, silicon nitride, and oxide films, as well as two-layered SiNx/SiO2 and three-layered SiO2/SiNx/SiO2 structures, were fabricated on p-type Si-substrates. The structure and element composition was studied by scanning electron microscopy and Rutherford backscattering spectroscopy, respectively. It was shown, spectral positions of photoluminescence maxima, as well as edge absorption, were determined by stoichiometry of SiNx layers. No electroluminescence signal was registered from single-layered silicon nitride films. The intense band at 1.9 eV dominated the electroluminescence spectra of single-layered silica film as well as two- and three-layered structures. It was attributed to silane groups in SiO2 layers. The contribution of emission from silicon nitride layers into electroluminescence of the two- and three-layered structures is discussed.

New approaches to enhance properties of silicon based quantum dot heterostructures for optical device application were developed. That is strain driven heteroepitaxy, small-sized quantum dots, elemental compositions of the heterointerface, virtual substrate, plasmonic effects, and the quantum dot charging occupation with holes in epitaxially grown Ge quantum dots (QDs) on Si (100). Experiments have shown extraordinary optical properties of Ge/Si QDs heterostructures and mid-infrared quantum dot photodetectors performance.

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.

Si-rich (SiN 1.1 ) and N-rich (SiN 1.5 ) silicon nitride films were grown on the Si wafers by plasma-enhanced chemical vapor deposition. Their composition and structure were investigated by Rutherford backscattering spectroscopy and transmission electron microscopy. The effect of composition and post-deposition annealing temperature on the SiN x light-emitting properties was investigated by the examination of photoluminescence. The intensive bands for the Si-rich and N-rich nitride films were detected in the red and blue spectral ranges, respectively. Photoluminescence bands transformations for the annealed nitride films can be ascribed to the increasing K- and N-centre concentration via the Si H and N H bonds rupture and the competitive processes of defect annihilation. On the basis of photoluminescence band FWHM broadening with “ x ” increasing, the FWHM dependence on the measurement temperature and SiN x films inhomogeneous structure, the emission from the SiN 1.1 and SiN 1.5 films is attributed to the transitions between the bands of defect and tail states associated with chemical disordering.

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.

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).

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.

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.

The radiative properties of non-stoichiometric silicon nitride SiNx fi lms produced by plasma-enhanced chemical vapor deposition were studied. Intense room-temperature photoluminescence (PL) in the visible region was recorded after annealing for both Si-rich (x = 1.13) and N-rich (x = 1.5) silicon nitride fi lms. The position of the PL band maximum depended signifi cantly on the fi lm composition. The PL band maxima for Si-rich and N-rich SiNx fi lms were detected in the red (660 nm) and blue (450 nm) spectral regions, respectively. The effect of the annealing atmosphere on PL of the SiNx fi lms was studied. It was shown that the PL intensity depended not only on the annealing temperature but also on the annealing atmosphere. The observed features of the non-stoichiometric SiNx PL spectra were explained in terms of defect states in the SiNx band gap.

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

with V and III Group Ions F. Komarov, L. Vlasukova, O. Milchanin, M. Grebena,∗, I. Parkhomenko, A. Mudryi, E. Wendler and P. Zukowski Belarusian State University, Nezavisimosti ave. 4, 220030 Minsk, Belarus Scienti c and Practical Materials Research Center, National Academy of Sciences of Belarus P. Brovki Str. 17, 220072 Minsk, Belarus Institut fur Festkorperphysik, Friedrich-Schiller-Universitat Jena, Max-Wien-Platz 1, D-07743 Jena, Germany Lublin University of Technology, Nadbystrzycka 38d, 20-618 Lublin, Poland

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.

CuInTe 2 is a semiconductor with high potential for use as a thermoelectric material and as the absorber in thin film solar cells. Studying the optical reflectivity spectra of CuInTe 2 single crystals resolves resonances at 1.054 eV and 1.072 eV, which are assigned to the A and B free excitons. Photoluminescence spectra exhibited a peak due to the A free exciton at 1.046 eV. Varshni coefficients were found for both excitons. Zero temperature bandgaps E gA = 1.060 eV and E gB = 1.078 eV were determined for the A and B valence sub-bands, respectively. The splitting due to crystal-field Δ CF and spin-orbit effects Δ SO were calculated as -26.3 meV and 610 meV, respectively, using the determined E gA and E gB and a literature value of E gC . © 2019 Author(s).

A new approach to the creation of circularly ordered Ge nanoislands by epitaxy on the surface of a heterophase structure consisting of a Si(100) substrate with premade seeds in the form of SiGe nanodisks or SiGe nanorings is developed. It is shown that the spatial configuration of islands in the group is due to the nucleation of the islands in the area of local minima of the elastic energy density on the surface of a circular seed. On the basis of this approach, a number of multilayer structures with vertically aligned ring groups of quantum dots were grown. The elemental composition and luminescent properties of the ordered structures are studied.

It is shown that a copper vapor laser can be used effectively for local crystallization of glasses with precipitation of active phases on a surface or in the interior volume of glass depending on its composition. Aprocedure is proposed for using a laser beam to form nanostructural waveguides with broadband near-IR luminescence peaking at 1300 – 1450 nm in glass with composition (mol.%) 7.5 Li2O, 2.5 Na2O, 20 Ga2O3, 35 GeO3 and 35 SiO2 doped with 0.1 – 0.5% NiO. A mechanism of self-limited laser heating, impeding subsequent growth of the nanocrystals formed, is demonstrated. The results of the investigations are of interest for developing active elements of integrated optics.

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.

CuInSe2 single crystals ion implanted with 5 keV hydrogen at doses from 3 × 1014 to 1016 cm−2 are studied by photoluminescence (PL). The PL spectra before and after implantation reveal two bands, a main dominant band centred at 0.96 eV and a lower intensity band centred at 0.93 eV. Detailed analysis of the shape of these bands, their temperature and excitation intensity dependencies allow the recombination mechanisms to be identified as band-to-tail (BT) and band-to-impurity (BI), respectively. The implantation causes gradual red shifts of the bands increasing linearly with the dose. The average depth of potential fluctuations is also estimated to increase with the dose and saturates for doses above 1015 cm−2. A model is proposed which associates the potential fluctuations with the antisite defects copper on indium site and indium on copper site. The saturation is explained by full randomization of copper and indium atoms on the cation sub-lattice.

Transmission, photoluminescence, and reflectance spectra of TlInS2 single crystals grown by the Bridgman–Stockbarger method were measured at 4.2 K near the fundamental absorption edge. Narrow lines at ~2.5535 and ~2.5694 eV were observed in the transmission spectrum and assigned to ground and excited free-exciton states, respectively. The free-exciton binding energy and band-gap energy Eg were found to be ~21.2 meV and ~2.5747 eV, respectively. A recombination mechanism was proposed for the TlInS2 near-band-edge and deep luminescence.

Solar cells with the structure ZnO:Al/i-ZnO/CdS/Cu(In,Ga)Se-2/Mo/polyimide were examined using a range of techniques. The elemental composition of the Cu(InGa)Se-2 (CIGS) layers, their crystalline structure and optical properties were studied. Photoluminescence (PL) spectra of the CIGS absorber layers were studied as functions of temperature (4.2-240 K) and excitation power density. The band gap energy E-g of the CIGS layers was determined by employing photoluminescence excitation (PLE) spectroscopy. The influence of sodium incorporation on the PL properties of CIGS was analysed. Correlations of the optical properties of the CIGS absorber layers and the photovoltaic parameters of the solar cells were revealed.

We have studied the ion-beam synthesis of GaSb nanocrystals in Si by high-fluence “hot” implantation of Sb and Ga ions followed by thermal annealing. The Rutherford backscattering, transmission electron microscopy/ transmission electron di˙raction, Raman spectroscopy and photoluminescence were used to characterize the implanted layers. It was found that the nanocrystal size increases from 5 to 60 nm in the samples annealed at 900 ±C up to 20–90 nm in those annealed at 1100 ±C. For the samples annealed at 900 ±C a broad band in the region of 0.75–1.05 eV is registered in the photoluminescence spectra. The nature of this photoluminescence band is discussed.

Thin films of Cu(In, Ga)Se2 (CIGS) with a Ga/(Ga + In) ratio of ~0.27 corresponding to the standard elemental composition for solar-energy transducers were grown on Mo-coated glass substrates by the Cu, In, Ga, and Se co-evaporation technique from different sources. Transmission (T), photoluminescence (PL), and photoluminescence excitation (PLE) spectra at 4.2 K were used to analyze electronic properties in the asgrown and electron-irradiated CIGS films. The band-gap energy (Eg) of the CIGS films measured using both transmission and PLE methods was found to be about 1.28 eV at 4.2 K. Two deep bands in the PL spectra of the irradiated CIGS films, P1 at ~0.91 eV and P2 at ~0.77 eV, have been detected. These bands are tentatively associated with copper atoms substituting indium (CuIn) and indium vacancies VIn, respectively, as the simplest radiation-induced defects.

The chemical composition of Cu(In,Ga)Se-2 (CIGS) semiconductor compounds is analyzed by local x-ray spectral microanalysis and scanning Auger electron spectroscopy. X-ray diffraction analysis reveals a difference in the predominant orientation of CIGS films depending on the technological conditions under which they are grown. The chemical composition is found to have a strong effect on the shift in the self-absorption edge of CIGS compounds. It is shown that a change in the relative proportion of Ga and In in CIGS semiconducting compounds leads to a change in the band gap E-g for this material in the 1.05-1.72 eV spectral range at 4.2 K.

The formation of nanodimensional InAs crystallites on Si wafers was studied by the method of high fluence implantation of As and In ions with subsequent high temperature treatment. It was found that the size and depth distributions of the crystallites depend on both the implantation temperature and the annealing conditions. A broad band in an energy range of 0.75–1.1 eV was recorded in the photolumines cence spectra of the samples.

Photoluminescence of CuInS2 single crystals grown by both the traveling heater method (THM) and chemical vapor transport (CVT) has been investigated at 4.2, 78, and 300 K. Intense emission in the near-band-edge region caused by free and bound excitons has been detected for both types of crystals. Taking into account the energy position of the luminescence line of the ground (n = 1) and first excited (n = 2) states, the binding energy for free A excitons has been estimated to be about 19.7 and 18.5 meV for CuInS2 grown by CVT and THM, respectively.

We have studied the luminescence and luminescence excitation spectra of erbium in the 1.54 µm region in titanium oxide and silicon oxide xerogels, formed in the mesoscopic pores of three-dimensional synthetic opals and two-dimensional porous aluminum oxide structures. For erbium-doped titanium oxide films formed in opal, in contrast to analogous films on porous aluminum oxide, in the luminescence excitation spectra we observe an intense broad band with a maximum in the ∼360 nm region. We discuss the possible nature of this band.

In this work the properties of indium tin oxide (ITO) films deposed on glass substrates by magnetron sputtering technique in the temperature range below 200 °C are studied by various methods. The physical properties of ITO thin films have been investigated using optical transmittance, photoluminescence, atomic force microscopy, ellipsometry, Hall-effect and four point probe methods. It is established that properties of ITO layers depend drastically on the temperature and oxygen partial pressure during the deposition process and exhibit some peculiarities of the surface morphology. It is found that the band gap energy of this material varies in the energy range from 4.1 to 4.4 eV and depends on the growth conditions. It is suggested that local deviations from the stoichiometry and defects are the main physical reasons of Burstein–Moss shift of the optical band gap.

Strain feld distribution at the surface of SiGe nanomounds formed by heteroepitaxy is exploited to obtain a positional ordering of the closely spaced Ge quantum dots (quantum dot molecules). We demonstrated, that a low density of the lateral quantum dot molecules (up to 107 cm−2) can be achieved by tuning of the growth conditions. We present a growth model that provide physical insights into possible mechanisms underlying the formation of lateral SiGe quantum dot molecules. The electronic band structure of the molecules was calculated by 6-band kp method. The results of theoretical study are in a good agreement with experimental measurements of photoluminescence spectra from the samples with quantum dot molecules.

Thin films of Cu2ZnSnSe4 (CZTSe) with copper deficiency and zinc excess were fabricated at Northumbria University by the selenisation of metallic precursors deposited on Mo/glass and bare glass substrates. Absorption and photoluminescence (PL) measurements were used to examine the film on glass whereas films on Mo/glass were used to produce a solar cell with efficiency of 8.1%. Detailed temperature and excitation intensity analysis of PL spectra allows identification of the main recombination mechanisms as band-to-tail and band-to-band transitions. The latter transition was observed in the spectra from 6 to 300 K. © 2015 IOP Publishing Ltd.

We have used low-temperature (4.2–78 K) photoluminescence to study defect formation processes in Cu(In,Ga)Se2 films when bombarded by protons with energy 380 keV. We have observed formation of luminescence centers with deep levels at ∼410 meV and 470 meV.

The bulk crystals of the CuAlTe2 semiconductor ternary compound with the chalcopyrite structure were prepared, and their optical properties were investigated. It was determined that the value of band gap energy equals 1.69 and 1.65 eV at 105 and 293 K, respectively. The photoluminescence spectra were measured for the first time and contain broad bands with peaks at 1.09 eV (78 K) and 1.03 eV (293 K). The full width at half maximum (FWHM) for both temperatures is 0.28 eV. The origin of this band is associated with band to deep acceptor optical transition. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Using photoluminescence and transmission measurements, we have studied the optical properties of indium nitride powder and thin films grown by molecular beam epitaxy. The bandgap for InN powder with electron concentration ∼ 4·1019 cm−3 was 0.94 eV, and for InN films with electron concentrations ∼1018 cm−3 it was 0.7 eV. We have established that when the electron concentration is increased to 8·1019 cm−3, the bandgap of InN increases to 1.0 eV. The change in the bandgap as a function of the concentration is due to the appearance of the Burstein-Moss effect.

Polycrystalline CuInGaSe 2 (CIGS) and CuInSe 2 (CIS) thin films were synthesized on glass substrates by a two-stage selenization process. The surface morphology, phase structure and composition of the films were analyzed by scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray analysis, respectively. Photoluminescence, optical transmission and reflection spectra were measured at temperatures from 4.2 to 300K to characterize defects and the structural quality. The structural quality and evolution of defects in the CIS films grown at different temperatures and selenization time, and dependence of the band-gap energy on the content of Ga in CIGS films at 78K is discussed.

The indirect- (Si) and direct- (ZnAs 2 , CuInSe 2 ) band-gap semiconductors, with E g of about 1 eV, ion-implanted with 350 keV Er, were studied using photoluminescence (PL). The PL spectra measured from each material revealed an emission line at about 1.54 μm associated with the internal 4f 11 transition ( 4 I 13/2 → 4 I 15/2 ) of Er. In the direct-gap semiconductors CuInSe 2 and ZnAs 2 , the Er-related emission was observed straight after the implantation and prior to any annealing whereas in Si such emission is only detectable after thermal annealing at 600 °C. The PL temperature dependencies from 4.2 to 300 K are discussed for all the materials.

Chalcopyrite polycrystalline CuInSe 2 (CIS) films with various elemental composition, synthesized by the two-stage selenization process on soda-lime glass substrates, were studied using photoluminescence (PL), photoluminescence excitation (PLE) and optical absorption (OA) techniques in the wide temperature range from 4.2 to 300 K in order to correlate the elemental composition with the optical properties of the material. For near-stoichiometric films (Cu/In≈1) intense free- and bound-exciton PL emission lines were observed at 4.2 K. At this temperature the A- and B-free exciton lines at E A =1.0409 and E B =1.0444 eV, respectively were found to be very narrow, with the full-width at half-maximum of about 2.5 meV, which is close to that of CIS single crystals. Well-resolved spectral lines of the A- and B-excitons were also observed in the OA and PLE spectra taken at 4.2 K. These excitonic lines remained intense at temperatures up to 78 K in both the OA and PL spectra. Deviations from stoichiometry significantly changed the PL spectra. The origin of the features observed in the PL spectra is discussed.

A survey of most recent studies of optical absorption, photoluminescence, photoluminescence excitation, and photomodulated reflectance spectra of single-crystalline hexagonal InN layers is presented. The samples studied were undoped n-type InN with electron concentrations between 6 × 10 18 and 4 × 10 19 cm -3 . It has been found that hexagonal InN is a narrow-gap semiconductor with a band gap of about 0.7 eV, which is much lower than the band gap cited in the literature. We also describe optical investigations of In-rich In x Ga 1-x N alloy layers (0.36 < x < 1) which have shown that the bowing parameter of b ∼ 2.5 eV allows one to reconcile our results and the literature data for the band gap of In x Ga 1-x N alloys over the entire composition region. Special attention is paid to the effects of post-growth treatment of InN crystals. It is shown that annealing in vacuum leads to a decrease in electron concentration and considerable homogenization of the optical characteristics of InN samples. At the same time, annealing in an oxygen atmosphere leads to formation of optically transparent alloys of InN-In 2 O 3 type, the band gap of which reaches approximately 2 eV at an oxygen concentration of about 20%. It is evident from photoluminescence spectra that the samples saturated partially by oxygen still contain fragments of InN of mesoscopic size.

The photoluminescence (PL) properties of combined Ge/Si structures representing a combination of large (200–250 nm) SiGe disk-like quantum dots (QDs) and the groups of smaller (40–50 nm) laterally ordered QDs grown on the nanodisk surface are studied. The experimental results are analyzed basing on the calculations of energy spectra, electron and hole wave functions. It is found that the strain accumulation in multi-layered structure is the main factor providing the room temperature PL. The new type of QD structures that should provide the observation of enhanced PL from SiGe QDs at room temperature is proposed. The structures represent the stacked compact groups of laterally aligned QDs incorporated in Si at the distance 30–40 nm above the large nanodisks.

CuInSe2 is a direct band gap semiconductor compound with chalcopyrite structure, which is used in solar cell absorber layers. The CuInSe2-based technologies are amongst the leaders for thin film photovoltaics (PV) in terms of conversion efficiency and stability. The very high absorption coefficient of CuInSe2, one of the highest in the region from 0.9 to 2.5eV (greater than 10 5 cm � 1 from 1.04eV) 1 amongst semiconductors used for solar cell absorbers, 2 provides an opportunity to reduce the absorber layer thickness down to submicron values. This lowers the cost of solar cells making them competitive against conventional sources of electricity. The 20.8% laboratory scale record for the conversion efficiency in CuInSe2-based solar cells 3 is, however, well below the theoretical limit of 30% for a single junction PV device 4 suggesting a lack of knowledge on the electronic properties of CuInSe2-based solar cells in general and of CuInSe2 in particular. Improvements in the structural quality of CuInSe2 by reducing the defect concentrations below a level where sharp excitonic features appear in the optical spectra make the methods of optical spectroscopy significantly more efficient and broaden the range of techniques available for analysis. Early optical spectroscopy studies of the excitonic properties of CuInSe2 revealed the complexity of the valence band, which is split into A, B, and C sub-bands by the simultaneous influence of the non-cubic crystal field and spin-orbit coupling. 5 Recently, the excitonic studies were extended by works based on new advances in the material structural quality 6‐9 determining accurate values of the A and B exciton binding energies Eb 7 and hole effective masses. 9 Significantly fewer papers however are concerned with the C exciton, although the C-band parameters are necessary for

Nanostructuring may impart new spectral luminescence properties to Ln-containing glasses untypical of disordered materials, which may considerably raise the competitiveness of the corresponding glass lasers and light transformers. Among the problems that can be solved by nanostructuring are obtaining Nd-containing glasses with an increased fraction of quanta emitted in the 4 F 3/2 4 I 13/2 transition ( λ ~ 1.34 μ m) and glasses characterized by efficient UV excitation of IR luminescence. These problems have remained topical for years for a number of practical applications. They are also of great interest from the viewpoint of materials science. This work is devoted to an attempt to obtain such

Using low-temperature (4.2–78 K) photoluminescence, we study the processes of defect formation in silicon films on sapphire irradiated with high-energy particles (electrons, γ-quanta of60Co). It is established that carbon atoms, as a residual process impurity, participate in the formation of luminescence centers stable up to annealing temperatures of about 550 K. For carbon-containing centers we reveal a shift in the spectral lines relative to their position in spectra of single-crystal silicon. It is proposed that this spectral shift is associated with the presence of internal stresses of about 5·108 N/m2 in the silicon films.

The free-exciton series with n=1,2 in high perfect CuInSe2 and CuGaSe2 single crystals have been observed in photoluminescence. The exciton binding energy and direct energy gap are estimated as 9.5 meV and 1.7305 eV at 4.2 K for CuGaSe2. New values are determined for the band gap energy Eg=1.0459 eV and for the excitonic binding energy 5.1 meV in CuInSe2 at 4.2 K. The temperature dependence of the n=1 excitonic line between 4.2 and 300 K have been studied.

Bulk crystals of the ternary CuAlTe2 semiconductor with chalcopyrite structure were prepared and their structural and optical properties, including transmission and reflectance, were investigated. It was evaluated that the value of optical gap energy equals 1.65 eV at 293 K. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)