Pair Recombination Luminescence Research Articles

Strategic improvement of Cu2SnS3 thin film by different heating rates and photoluminescence investigation

Cu2SnS3 (CTS) thin films have been synthesized on molybdenum-coated soda lime glass substrates by sulfurization the Cu-Sn alloy precursors grown by radio-frequency magnetron sputtering technique. Strategic improvement has been carried out on the composition, structural, morphological and optical properties of CTS thin films sulfurized by rapid heating rate and slow heating rate. The annealing heating rate can adjust the ratio of Cu/Sn, improve the crystallinity and surface morphology. The ratio of Cu/Sn is close to the stoichiometric composition of CTS under slow heating rate with more loss of Sn. Structural characterization exhibits the CTS thin film sulfurized by slow heating rate has a better crystallinity without secondary phase. The CTS thin film obtained at slow heating rate presents a larger average grain size and smooth surface. The optical band gap of CTS thin films is at the vicinity of 0.87 eV. Photoluminescence (PL) spectroscopy has been used to study the carrier recombination mechanism and the electronic structure of CTS thin film by excitation power and temperature dependent measurements. The peak observed from PL spectra of CTS thin film conforms to the donor-acceptor pair recombination luminescence.

Exciton luminescence from Cu2SnS3 bulk crystals

The optical properties of Cu2SnS3 (CTS) bulk crystals grown by chemical vapor transport were studied by photoluminescence (PL) spectroscopy. The PL spectra from the CTS bulk crystals were analyzed as a function of excitation power and temperature. The main phase of the as-grown samples was determined to be monoclinic CTS by Raman spectroscopy. The observed PL spectra from the CTS bulk crystals were composed of peaks corresponding to free-exciton, two bound-excitons, and donor-acceptor pair recombination luminescence. The peak energies for the free-exciton and two bound-exciton emissions were 0.9317, 0.9291, and 0.9260 eV, respectively, at temperature of 4.2 K. The bound-exciton luminescence was not observed above 30 K. The thermal activation energies for the free-exciton and two bound-exciton emissions were 6.5, 4.8, and 5.2 meV, respectively. The fundamental band gap in the CTS bulk crystals was expected to be ca. 0.94 eV.

Donor-acceptor pair recombination luminescence from monoclinic Cu2SnS3 thin film

The defect levels in Cu2SnS3 (CTS) were investigated using photoluminescence (PL) spectroscopy. A CTS thin film was prepared on a soda-lime glass/molybdenum substrate by thermal co-evaporation and sulfurization. The crystal structure was determined to be monoclinic, and the compositional ratios of Cu/Sn and S/Metal were determined to be 1.8 and 1.2, respectively. The photon energy of the PL spectra observed from the CTS thin film was lower than that previously reported. All fitted PL peaks were associated with defect related luminescence. The PL peaks observed at 0.843 and 0.867 eV were assigned to donor-acceptor pair recombination luminescence, the thermal activation energies of which were determined to be 22.9 and 24.8 meV, respectively.

Luminescence characteristics of the LPE‐grown undoped and In‐doped ZnO thin films and bulk single crystals

AbstractThe time‐resolved emission spectroscopy using the fs‐laser pulse and ps X‐ray excitations was employed to compare the luminescence characteristics of the liquid phase epitaxy grown ZnO films and the hydrothermally grown single crystals. Reabsorption of the excitonic emission is demonstrated in the bulk ZnO. In the In‐doped films the donor‐acceptor pair recombination luminescence was evidenced above 400 nm and its decay was found to obey the t–1 law. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic structure of intrinsic defects and mechanism of donor-acceptor pair luminescence in CuI crystal

The electronic structures of γ phase copper iodide crystal and the intrinsic point defects associated with iodine and copper have been studied with relativistic density functional theory and embedded cluster method. The simulations for point defects show that the tetrahedron interstitial copper atoms and copper vacancies may lead to the shallow donor and acceptor levels in the energy gap, which is related with the origins of the broad donor-acceptor pair recombination luminescence band 420—430 nm of CuI crystal.

Effect of the isotopic mass of gallium on the indirect gap of GaP

We have obtained pair recombination luminescence spectra of four GaP crystals with different gallium isotopic compositions. The frequency shifts measured vs. average isotopic mass allow us to determine dE 0/ dM=0.19(1) meV/ amu , where E 0 is the indirect gap and M the average gallium isotopic mass. From this mass derivative, a contribution of the gallium vibrations to the zero-point mass renormalization of the gap of 27 meV is estimated. Subtracting this contribution from the total zero point renormalization, as determined from the temperature dependence of the indirect gap, yields a contribution of 59 meV of the phosphorus vibrations to the gap renormalization. These results are discussed in comparison with similar data for group IV, III–V, and II–VI semiconductors. A comparison with theoretical calculations is also presented.

Time-resolved donor-acceptor pair recombination luminescence in highly n- and p-doped II–VI semiconductors

Time resolved luminescence measurements of the donor-acceptor pair (DAP) luminescence of n-doped CdS:In bulk crystals, undoped bulk ZnSe crystals grown with various VI/II ratios, and p-doped ZnSe:N epilayers in the near band gap region are presented. The decay of the donor-acceptor pair recombination luminescence is investigated for dopant concentrations below the Mott density. A discussion on the basis of a statistical theory by Thomas and Hopfield for DAP recombination yields, by knowledge of the Bohr radii of the impurities, the number of electronically active impurity centres. The reliability of this method to determine impurity concentrations is discussed.

Dynamical aspects of edge luminescence in orthorhombic InI

Edge luminescence in orthorhombic indium iodide has been investigated under pulsed dye laser excitation at liquid helium temperature. Emission spectra consist of several lines with approximately the LO phonon energy spacing C̵ω LO (13.8 meV). Time-resolved spectra reveal bound exciton (BE) luminescence and donor-acceptor (DA) pair recombination luminescence. The spectral shape changes strongly with time. The fast component (τ<10 ns) consists of the bound exciton BE 0 peak followed by LO-phonon side bands. The slow component (τ<100 ns) is composed of a no-phonon component DA 0 followed by several LO-phonon replicas. This series of peaks shifts to lower energy with time. An anti-Stokes component appears at the DA 0 peak with significant intensity for the laser energy lower than that of the first member of the series, DA 0. This component is interpreted to originate from the cascade excitation of electrons (holes) at deeper traps.

Radiated recombination in CdGa 2Se 4

The photoluminescence of single crystals of CdGa 2Se 4 is studied as a function of temperature, of the excitation intensity, and of the polarization of the exciting light. A possible level scheme for optical transitions in the perfect crystal is given and evidence is also found for donor-acceptor pair recombination luminescence.

Sharp-line, donor–acceptor pair recombination luminescence in Si(In,Li), Si(Ga,Li), Si(Al,Li), and Si(B,Li)

The observation of sharp-line, donor–acceptor pair recombination luminescence in Si following the diffusion of the donor Li into samples previously doped with the acceptors B, Al, Ga, or In is reported. Shell assignments have been made for most of the numerous new photoluminescence lines. These assignments indicate that the principal donor introduced into the samples was the Li–O complex, and that the principal acceptor in the In-doped samples was the In–X centre. Results for the Al- and Ga-doped samples are consistent with ordinary Al and Ga acceptors, while those for B are inconclusive due to the extreme weakness of the sharp-line structure. This study not only confirms that donor–acceptor pair recombination in Si can give rise to sharp luminescence line series, but shows that this process is quite widespread, given the proper concentrations of donors and acceptors.