A. V. Mudryi

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 (EgA=1.050 eV and EgB=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.

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

Intense blue luminescence of anodic aluminum oxide

The luminescence spectra of aluminum oxide with an ordered system of through pores have been studied. The diameter and density of pores were ≈ 50 nm and 1.2 × 1010 cm−2, respectively. Amorphous aluminum oxide formed by anodization of aluminum foil in an oxalic acid electrolyte shows intense luminescence in the blue spectral region. Processing of spectra with the use of an oxalic acid approximation by Gaussian curves gives three bands peaking at ∼ 382 (3.2 eV), 461 (2.7 eV), and 500 nm (2.5 eV), which correspond to different types of defects. The bands at 382 and 461 nm can be assigned to optical transitions involving F+ and F centers (vacancies of oxygen with one or two electrons), respectively. The lower-energy band near 500 nm can be presumably assigned to luminescence from F++ centers (vacancy of oxygen without an electron). Analysis of the luminescence excitation spectra has revealed an inhomogeneous character of the distribution of the corresponding luminescence centers in the Al2O3 matrix.

Determination of the Structural and Optical Characteristics of Cu 2 ZnSnS 4 Semiconductor Thin Films

The results of X-ray diffraction and optical studies of Cu2ZnSnS4 films produced by the flash evaporation of binary sulfide compounds under different technological conditions is reported. It is shown that it is possible to produce Cu2ZnSnS4 films, rather perfect in structural and optical respects, by choosing the optimal annealing temperatures at different Ar vapor pressures. The lattice parameters of the compounds are determined. The systematic shift in the photoluminescence bands under variations in the excitation level is established. It is found that the characteristics of the bands depend to a large extent on the annealing temperature, the Ar pressure during thermal treatment, and the resultant stoichiometry composition of the samples. It is shown that Raman studies and luminescence measurements can be used to assess the quality of the synthesized Cu2ZnSnS4 films and to obtain data on the energy structure of defects in the band gap.

Terbium photoluminescence in yttrium aluminum garnet xerogels

Based on a colloidal solution containing terbium, yttrium, and aluminum metal ions, a powder was synthesized and films of terbium-doped yttrium aluminum garnet Tb0.15Y2.85Al5O12 were grown on single-crystal silicon and porous anodic alumina. Annealing of the sample in a temperature range from 200–1100°C results in an increase in the photoluminescence intensity in the wavelength range from 480–640 nm, which is caused by Tb3+ ion intra-atomic transitions 5D4→7Fj (j = 3, 4, 5, 6). Annealing at 900°C and higher temperatures gives rise to low-intensity photoluminescence bands in the region of 667 and 681 nm, which correspond to transitions 5D4→7F0, 5D4→7F1, and room-temperature Stark term splitting, which suggests the existence of a crystalline environment of Tb3+ ions. The FWHM of spectral lines in the region of 543 nm decreases from ∼10 to ∼(2–3) nm as the xerogel annealing temperature is increased from 700 to 900°C and higher. Three bands with maxima at 280, 330, and 376 nm, which correspond to Tb3+ ion transitions 7F6→5I8, 5L6, 5G6, 5D3, are observed in the photoluminescence excitation spectra of the studied structures for the emission wavelength at 543 nm. X-ray diffraction detected the formation of a crystalline phase for a terbium-doped yttrium aluminum garnet powder after annealing at 1100°C.

Photoluminescence of erbium-doped aluminum oxide films with embedded silicon nanoparticles

Erbium-doped aluminum oxide films with embedded Si nanoparticles have been obtained by magnetron puttering of a composite (Al + Er2O3 + Si) target and subsequent electrochemical anodization at room temperature. The photoluminescence (PL) spectra of these films are measured in the temperature range 4.2–300 K. Efficient PL is observed at a wavelength of 1.54 μm without preliminary annealing of the samples, which indicates the possibility of activating Er3+ ions without any high-temperature treatment. The aluminum oxide films with embedded Si nanoparticles were observed to show stronger PL at a wavelength of 1.54 μm than similar films without Si nanoparticles. This effect can be explained by additional pumping of Er-based luminescence centers and energy transfer from the Si nanoparticles.

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 − 2

Optical properties of synthetic diamond single crystals

Synthetic diamond single crystals were grown by the thermal gradient method in a high-pressure apparatus in the presence of solvent catalysts (nickel, iron). Absorption, luminescence, and photoluminescence excitation measurements were performed in order to determine the nature of impurity-defect complexes in both as-grown crystals and crystals treated at high temperature (T≈2000–2200 K) and high pressure (P≈6.0–6.5 GPa). Different luminescence and absorption bands were assigned to impurity centers containing nitrogen and nickel atoms.

Optical spectroscopy of excitonic states in zinc diarsenide

The luminescence and transmission of zinc diarsenide single crystals near the fundamental absorption edge have been investigated in the temperature range 4.2–300 K. Intense luminescence and absorption lines at 1.0384, 1.0488, and 1.0507 eV, referring to the ground state (n=1) and excited states (n=2, n=3) of a free exciton were observed at low temperatures. The free-exciton binding energy was found to be ∼13.9 meV on the basis of the hydrogen-like model and the direct band gap was found to be 1.0523, 1.0459, and 0.9795 eV at 4.2, 78, and 300 K, respectively.

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.