The electronic structure of the oxygen vacancy in ZnO has been found to be sensitive to the corrections applied to the local (spin) density approximation (LSDA) band gap underestimate. Here, the ``$\mathrm{LSDA}+U$'' approach, in which Hubbard-$U$ corrections are added to the local density approximation, is applied to both $\mathrm{Zn}\phantom{\rule{0.2em}{0ex}}d$ and $\mathrm{Zn}\phantom{\rule{0.2em}{0ex}}s$ orbitals. The justification of this approach is discussed. Transition state energies are calculated self-consistently instead of applying a posteriori corrections. The supercell size dependence and applicability of Makov--Payne corrections is investigated and an extrapolation approach inversely proportional to the cell volume is used. The $0∕2+$ transition level is found at $0.80\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above the valence-band maximum and a small negative $U$ behavior is obtained with $U=\ensuremath{-}0.05\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The Kohn--Sham one-electron levels in the different charge states are also presented and relevant experimental results are discussed.

First-principles calculation of the O vacancy in ZnO: A self-consistent gap-corrected approach

The red shift and the broadening of the Raman signal from microcrystalline silicon films is described in terms of a relaxation in the q-vector selection rule for the excitation of the Raman active optical phonons. The relationship between width and shift calculated from the known dispersion relation in c-Si is in good agreement with available data. An increase in the decay rate of the optical phonons predicted on the basis of the same model is confirmed experimentally.

The one phonon raman spectrum in microcrystalline silicon

We demonstrate the complete tunability of a general strategy to intercalate zero-valent atoms into two-dimensional (2D) layered materials. A chemical method was used to intercalate high densities of copper (up to 55 atomic percent) into synthesized nanomaterials such as MoO3, Sb2Te3, In2Se3, and GaSe. These materials were characterized using TEM, EDX, electron diffraction, XRD, Raman, EELS, and XPS to observe the effects of intercalation, determine the concentration of copper, and confirm the zero-valent nature of the intercalant as well as unchanged structure of the host material. This technique reveals the power and potential to observe unique chemical and physical phenomena and to control such properties for particular applications.

/pdf/general-strategy-for-zero-valent-intercalation-into-two-4th787ya41.pdf

General Strategy for Zero-Valent Intercalation into Two-Dimensional Layered Nanomaterials

Action of a laser-induced plane shock wave has been considered as the mechanism of doping of CdTe surface region with In. CdTe crystals coated with a relatively thick In film were subjected to irradiation with KrF excimer laser pulses. The In film was not completely evaporated under irradiation and it served further as an electrode in the fabrication of nuclear radiation detectors. Dopant atoms, implicated by laser-induced stress and shock waves, penetrated into CdTe. An In-enriched region was formed and a built-in p-n junction arose at the depth where a stress wave was converted to a shock wave.

Laser-induced shock wave stimulated doping of CdTe crystals

We review prior and on-going works in using laser annealing (LA) techniques in the development of chalcogenide-based [CdTe and Cu(In,Ga)(S,Se)2] solar cells. LA can achieve unique processing regimes as the wavelength and pulse duration can be chosen to selectively heat particular layers of a thin film solar cell or even particular regions within a single layer. Pulsed LA, in particular, can achieve non-steady-state conditions that allow for stoichiometry control by preferential evaporation, which has been utilized in CdTe solar cells to create Ohmic back contacts. Pulsed lasers have also been used with Cu(In,Ga)(S,Se)2 to improve device performance by surface-defect annealing as well as bulk deep-defect annealing. Continuous-wave LA shows promise for use as a replacement for furnace annealing as it almost instantaneously supplies heat to the absorbing film without wasting time or energy to bring the much thicker substrate to temperature. Optimizing and utilizing such a technology would allow production lines to increase throughput and thus manufacturing capacity. Lasers have also been used to create potentially low-cost chalcogenide thin films from precursors, which is also reviewed.

https://www.spiedigitallibrary.org/journals/journal-of-photonics-for-energy/volume-5/issue-1/050999/Laser-processing-for-thin-film-chalcogenide-photovoltaics--a-review/10.1117/1.JPE.5.050999.pdf

Laser processing for thin film chalcogenide photovoltaics: a review and prospectus

The dynamics of modification of the surface structure in p-CdTe (111) crystals subjected to nanosecond ruby laser pulses with a lasing wavelength within the fundamental-absorption region (ℏω=1.78 eV) is studied. It is shown that, depending on the radiation dose, the surface morphology changes in the following order: the formation of tellurium film, an increase in the density of dislocations under the tellurium film, and the formation of ordered quasi-periodic structures of both micrometer and nanometer size. The size of the structures and the character of their distribution are shown to be dose-dependent.

The Evolution of Surface Structures in p -CdTe Crystals under Pulsed Laser Irradiation

Photoelectric properties of cadmium telluride films subjected to laser radiation

The effect of a threshold process of surface melting on the acoustic response in CdTe and GaAs subjected to pulsed laser radiation is considered and the mechanisms of excitation of sonic signals are analyzed. Melting thresholds of the surface of binary compounds CdTe and GaAs are established under irradiation by pulses of nanosecond duration of ruby and neodymium lasers from measurements of the amplitude of the acoustic response.

Effect of melting on the acoustic response of CdTe and GaAs subjected to the pulsed laser irradiation

Variations in the minority-carrier lifetime, photoluminescence spectra, dark current and photocurrent temperature dependences of high-resistivity p-CdTe crystals under the action of the laser shock wave are investigated. It is shown that the variations in the aforementioned characteristics during the passage of the shock wave are defined by the generation of the nonequilibrium carriers from deep centers, and, after that, the variations are defined by the formation of intrinsic defects and their subsequent interaction with the defects existing in the initial crystals.

Variation in the defect structure of p-CdTe single crystals at the passage of the laser shock wave

Atomic-force spectroscopy and Raman scattering are applied to study structural modification of the p-CdTe (111) surface under exposure to pulsed multimode ruby laser radiation of nanosecond duration and a power density below the material-melting and destruction thresholds. It is shown that irradiation of crystals produces nanometer quasi-ordered surface nanoclusters 1.0–11.3 nm in height with a lateral size of 41–336 nm. Possible mechanisms of their formation are discussed.

P. E. Mozol

Papers

The Evolution of Surface Structures in p -CdTe Crystals under Pulsed Laser Irradiation

Photoelectric properties of cadmium telluride films subjected to laser radiation

Effect of melting on the acoustic response of CdTe and GaAs subjected to the pulsed laser irradiation

Variation in the defect structure of p-CdTe single crystals at the passage of the laser shock wave

Atomic-force microscopy and Raman scattering studies of laser-induced structural disordering on the p-CdTe surface