Excitation power and temperature dependence of excitons in CuInSe2

Excitonic recombination processes in high quality CuInSe2 single crystals have been studied by photoluminescence (PL) and reflectance spectroscopy as a function of excitation powers and temperature. Excitation power dependent measurements confirm the identification of well-resolved A and B free excitons in the PL spectra and analysis of the temperature quenching of these lines provides values for activation energies. These are found to vary from sample to sample, with values of 12.5 and 18.4meV for the A and B excitons, respectively, in the one showing the highest quality spectra. Analysis of the temperature and power dependent PL spectra from the bound excitonic lines, labelled M1, M2, and M3 appearing in multiplets points to a likely assignment of the hole involved in each case. The M1 excitons appear to involve a conduction band electron and a hole from the B valence band hole. In contrast, an A valence band hole appears to be involved for the M2 and M3 excitons. In addition, the M1 exciton multiplet seems to be due to the radiative recombination of excitons bound to shallow hydrogenic defects, whereas the excitons involved in M2 and M3 are bound to more complex defects. In contrast to the M1 exciton multiplet, the excitonic lines of M2 and M3 saturate at high excitation powers suggesting that the concentration of the defects involved is low. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709448

Diamagnetic shift of the A free exciton in CuGaSe2 single crystals

Single crystals of CuGaSe2 were studied using magnetophotoluminescence inmagnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82 x 10(-6) eV/T-2. This rate was used to calculate the reduced mass as 0.115m(0), the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m(0) (m(0) is the free electron mass) of the free A exciton using a low-field perturbation approach and the hydrogenic model

Excited states of the free excitons in CuInSe2 single crystals

High-quality CuInSe2 single crystals were studied using polarization resolved photoluminescence (PL) and magnetophotoluminescence (MPL). The emission lines related to the first (n=2) excited states for the A and B free excitons were observed in the PL and MPL spectra at 1.0481 meV and 1.0516 meV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 meV and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E-g(A)=1.050 eV and E-g(B)=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model

A photoluminescence study of CuInSe2 single crystals ion implanted with 5 keV hydrogen

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

Ion Beam Synthesis of InAs Nanocrystals in Crystalline Silicon

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

Optical properties of high quality Cu2ZnSnSe4 thin films

Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectr

A photoluminescence study of excitonic grade CuInSe2 single crystals irradiated with 6 Mev electrons

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

Electronic energy band parameters of CuInSe2 : Landau levels in magnetotransmission spectra

Magnetotransmission (MT) at magnetic fields up to 29 T was used to study the electronic structure of CuInSe2 in thin polycrystalline films. The zero field absorption spectra exhibited resolved A, B, and C free excitons. Quantum oscillations, due to diamagnetic excitons comprising electrons and holes from Landau levels quantized in the conduction and valence band, respectively, appeared in the MT spectra at fields over 5 T. Spectral energies of Landau levels and binding energies of the corresponding diamagnetic excitons, theoretically calculated assuming a quasicubic approximation of the CuInSe2 tetragonal lattice structure, helped to identify the character of the experimentally observed diamagnetic excitons. Spectral energies of diamagnetic excitons in the MT spectra with different circular polarizations were used to determine the electron and light hole effective masses, whereas heavy hole masses as well as the γ and γ1 Luttinger parameters, Ep Kane energy, and F parameter of the influence of remote bands, as well as their polaron values, were calculated using the Luttinger theory

Stimulated emission and lasing in Cu(In,Ga)Se2 thin films

Stimulated emission and lasing in Cu(In,Ga)Se 2 thin films have been demonstrated at a temperature of 20 K using excitation by a nanosecond pulsed N 2 laser with power densities in the range from 2 to 100 kW cm − 2 . Sharp narrowing of the photoluminescence band, superlinear dependence of its intensity on excitation laser power, as well as stabilization of the spectral position and of the full-width at half-maximum of the band were observed in the films at increasing excitation intensity. The stimulated emission threshold was determined to be 20 kW cm − 2 . A gain value of 94 cm − 1 has been estimated using the variable stripe length method. Several sharp laser modes near 1.13 eV were observed above the laser threshold of I thr ~ 50 kW cm −