Gennadiy A. Medvedkin

Room Temperature Ferromagnetism in Novel Diluted Magnetic Semiconductor Cd1¡xMnxGeP2

High concentration of Mn atoms has been incorporated in the surface region of II-IV-V2 type chalcopyrite semiconductor CdGeP2. Photoluminescence spectrum at 20 K shows a peak around 3.2 eV, suggesting that the incorporation of Mn introduces an energy gap much higher than that of the host semiconductor (Eg=1.83 eV). Prominent magnetic hysteresis loops with coercivity of 0.5 kOe has been observed at room temperature. Magnetic force microscope (MFM) measurements reveal a stripe-shaped domain pattern on the top surface. Magneto-optical Kerr ellipticity spectrum measured at room temperature show a prominent peak at 1.7 eV and a broad tail up to 3.5 eV. We tentatively attribute the ferromagnetism to the double exchange interaction between Mn2+ and Mn3+ states due to the structural feature of II-IV-V2 type chalcopyrite compounds.

Ferromagnetic phenomenon revealed in the chalcopyrite semiconductor CdGeP2:Mn

High concentration of Mn atoms has been successfully incorporated into the chalcopyrite type II–IV–V2 semiconductor CdGeP2 by solid-state reaction technique without causing any structural changes. Polycrystalline powder of the chalcopyrite-related material in Cd–Mn–Ge–P quaternary system has been additionally synthesized by sintering technology. Well-defined M–H hysteresis loops were observed at room temperature in CdGeP2:Mn single crystal and polycrystalline powder samples grown independently. The Curie temperature has been determined to be 320 K for single crystal phase CdxMn1−xGeP2 and 310 K for the polycrystalline powder. Magnetic force microscopy (MFM) observation clearly showed a stripe domain pattern on the Mn-diffused surface of CdGeP2 single crystal. The magneto-optical Kerr ellipticity spectrum of CdGeP2:Mn crystal showed a peak around 1.75 eV at T=300 K.

Thermal oxidation of CuInSe2: Experiment and physico-chemical model

Abstract The thermal oxidation of CuInSe 2 single crystals and bulk polycrystalline plates of n- and p-type conductivity with polished facets have been carried out at elevated temperatures of 400 to 610°C in dry oxygen/air atmosphere. All crystals demonstrated an enhancement in hole conductivity near the surface. Additionally, transparent layers of In 2 O 3 chemical composition grew on the surface. Electron-probe analysis, Rutherford backscattering, X-ray diffraction, and optical and photoelectric experimental data have provided a basis to develop a physico-chemical model for the thermal oxidation of CuInSe 2 crystals. The model includes the In 2 O 3 compound appearance, V Se , V Cu vacancy absorption, Se i , Cu i extra atom and Cu x Se generation. The chemical reactions are accompanied by arising dislocations and mechanical stresses at the In 2 O 3 /CuInSe 2 interface.

Electron Paramagnetic Resonance and Photoluminescence Study of Defects in CuGaSe2 Single Crystals Grown by the Traveling Heater Method

Electron paramagnetic resonance (EPR) at T = 4.2 K and photoluminescence (PL) spectra at T = 20 K have been employed to elucidate point defect features in CuGaSe2 crystals grown by the traveling heater method. Isotropic and anisotropic paramagnetic centers have been found in crystals as-grown and annealed in various gas mediums. Three PL bands have been observed and the influence of H2, O2 and Se2 annealing has been studied. The presence of donor singlet VSe+ has been evidenced in as-grown and H2 annealed crystals. Complex study of EPR, PL spectra and defect physics models have allowed the addition of the point defect ensemble in CuGaSe2 with defect pairs (2VCu- + GaCu2+), VCu and other defect complexes, according to treatments used in this work.

Photoluminescence of CdSnP2 Single Crystals in the Vicinity of the Fundamental Optical Edge

The influence of chemical etching on the emission properties of undoped CdSnP2 crystals has been studied. The appropriate treatment gives rise to integral strengthening of photoluminescence and redistribution of emissions in such a manner that the longest wavelength band disappears and the exciton line flames up. The shortest wavelength line at 1.243 eV with the 2kT half-width has been observed successfully for the first time. The doublet structure observed near the fundamental optical edge was attributed to the free exciton and bound-to-shallow level state in CdSnP2.

Computer modeling and visualization of hidden defects in thin film solar cells on CuInSe2 and Cu(In,Ga)Se2

The laser scanning technique was used to realize two- and three-dimensional optoelectronic images of polycrystalline solar cells based on thin films of CuInSe2 and CuInGaSe2. Topograms obtained with the aid of the laser-beam-induced current and computer modeling reveal microregions with reduced photovoltaic efficiency and provide a detailed picture of distribution of hidden inhomogeneities over the entire active surface of the solar cells. Gradation of the microdefects with intensity and size has been achieved using post-experimental graphic and false-color processing of the obtained three-dimensional images.

Optical sensors sensitive to the light polarization: Phenomenological consideration through electronic parameters

The polarization coefficient dependences on a depth of embedding p-n junction, diffusion length of minor charge carriers, surface recombination rate and lifetime of the carriers have been derived and analyzed numerically for optical sensors sensitive to the light polarization. The characteristic electronic parameters are shown to change dramatically the magnitude and sign of photopleochroism coefficient.