V. R. Romanyuk

Metal nanoparticle-enhanced photocurrent in GaAs photovoltaic structures with microtextured interfaces

The photocurrent enhancement effect caused by Au and Ag nanoparticles for GaAs-based photovoltaic structures of surface barrier or p-n junction type with microtextured interfaces has been investigated in dependence on the conditions of nanoparticles deposition and, respectively, on the shape and local dielectric environment of obtained nanoparticle arrays. Three nanoparticle deposition methods have been checked: 1) photoinduced chemical deposition of Au from aqueous AuCl3 solution forming nanowires on the ridges of quasigrating-type surface microrelief, 2) deposition of Ag nanoparticles from colloidal suspension on the GaAs substrate covered with poly(vinylpyridine), and 3) drop and dry deposition of Au/SiO2 core-shell nanoparticles from aqueous colloid solution. The comprehensive investigation of optical reflectance, photoelectric, and electrical characteristics of the fabricated barrier structures has shown the highest photovoltaic parameters for surface microrelief of quasigrating-type and electroless Au nanoparticle deposition. The analysis of characteristics obtained allowed us also to define the mechanisms of the total photocurrent enhancement.

Effect of Fe, Co, and Cr impurities on the thermoelectric properties of Cd x Hg1−x Se

We have studied the effect of doping with 3d transition metals (iron, cobalt, and chromium) on the thermoelectric properties of single crystals of CdxHg1−xSe solid solutions at temperatures from 77 to 400 K and the effect of thermal annealing in Hg or Se vapor on their electrical properties. The results indicate that chromium and cobalt produce no energy levels in the band structure of CdxHg1−xSe solid solutions. Therefore, these dopants do not create resonant donor levels superimposed on continuum states of mercuric selenide. Fe doping produces an energy level whose position can be controlled by varying the composition of the solid solutions.

The physical properties of CdTe doped with V and Ge

CdTe:(V, Ge) single crystals are grown using the Bridgman-Stockbarger method. The impurity concentrations in the melt are NV = 1 × 1019 cm−3 and NGe = 5 × 1018 and 1 × 1019 cm−3. Electrical and galvanomagnetic characteristics are studied in the temperature range 300–400 K. It is found that the equilibrium characteristics are governed by deep levels (ΔE = 0.75–0.95 eV) located close to the midgap. Low-temperature optical absorption spectra indicate that the impurity levels of V and Ge ions in the low-energy region are in different charge states. In addition, the samples are annealed in Cd vapor and then rapidly cooled. This annealing causes the decomposition of various complexes formed during the crystal growth and an increase in both electrical conductivity and charge carrier concentration.

Electrical properties and microstructure of CdxHg1 − x − yCrySe crystals

Crystals of the CdxHg1 − x − yCrySe (x = 0.4, y = 0.1) quaternary solid solution have been grown by the Bridgman method, and their microstructure and electrical properties have been studied. The crystals are shown to contain various types of inclusions in the form of filaments and triangles.

Magnetic ordering in CrxHg1 − xSe crystals grown by solid-state recrystallization

CrxHg1 − x crystals grown by solid-state recrystallization have been characterized by electron paramagnetic resonance spectroscopy, transport measurements, and X-ray microanalysis. The results demonstrate that the crystals contain rectangular HgCr2Se4 inclusions elongated along one of their axes and irregularly shaped CrxHg1 − x and CrHg inclusions. In the range 77–400 K, the electrical properties of samples cut from different parts of the crystals are typical of semiconductors with a strongly degenerate electron gas.

OPTICAL AND PHOTOELECTRIC INHOMOGENEITY OF CdTe:V CRYSTALS

The optical and photoelectric properties of CdTe:V crystals with the doping impurity concentration NV = 5·1018–5·1019 cm−3 are investigated and the possibility of their use as a photorefractive material is considered. As is seen from the spectra of optical transmission, the crystals of both types possess high transparency (50–65%), which for CdTe:V specimens with NV = 5·1019 cm−3 decreases sharply and in the range 12–14 μm does not exceed 5%, whereas for CdTe:V crystals with vanadium concentration of 5·1018 cm−3 such a value of transmission remains unchanged up to 25 μm, implying a good optical quality of the latter crystals and their possible application in the spectral range 1.06–1.25 μm in modern fiber-optic communication lines.