Comparison between results of optical and electrical measurements of free electron concentration in n-InAs specimens

A theoretical model has been developed for determining the free electron concentration in n-InAs specimens from characteristic points in far IR reflection spectra. We show that this determination requires plasmon-phonon coupling be taken into account, otherwise the measured electron concentration proves to be overestimated. A correlation between the electron concentration Nopt and the characteristic wavenumber ν+ has been calculated and proves to be well fit by a third order polynomial. The test specimens have been obtained by tin or sulfur doping of indium arsenide. The electron concentration in the specimens has been measured at room temperature using two methods: the optical method developed by the Authors (Nopt) and the conventional four-probe Hall method (the Van der Pau method, NHall). The reflecting surfaces of the specimens have been chemically polished or fine abrasive ground. The condition Nopt > NHall has been shown to hold for all the test specimens. The difference between the optical and the Hall electron concentrations is greater for specimens having polished reflecting surfaces. The experimental data have been compared with earlier data for n-GaAs. A qualitative model explaining the experimental data has been suggested.

Динамика решетки и электронные свойства нелинейного кристалла BaGa-=SUB=-2-=/SUB=-GeS-=SUB=-6-=/SUB=-: комбинационное рассеяние, ИК отражение и расчет ab initio

We have measured the polarized Raman scattering and IR reflection spectra of a BaGa_2GeS_6 crystal, the Ga and Ge atoms of which are disordered, randomly occupying crystallographic positions of the same kind. The IR reflection spectra have been processed by the dispersion analysis method. The dispersion of phonons, the density of phonon states, the electronic band structure, and the partial densities of electronic states have been calculated in the DFT approximation using the alchemical potential method for disordered Ga and Ge atoms. It has been found that the stretching vibrations in the vibrational spectra are separated from the bending modes by a gap of about 100 cm^–1 and that the band structure of the crystal has an indirect energy gap.

Синтез и оптические свойства пленок оксида титана, модифицированных кобальтом

Using X-ray phase analysis, scanning electron microscopy atomic force and magnetic force microscopy, and IR spectroscopy the properties of polycrystalline TiO2 films modified by cobalt during magnetron sputtering and subsequent pulsed photon processing in air have been investigated. It has been found that in the course of the modification, a nanocrystalline (with a grain size of ~ 50 nm) film consisting of cobalt and titanium oxides is formed. Their surface exhibits magnetic properties. In the IR reflection spectra obtained at different incident angle of beam, two of the transverse optical (TO) phonons and their corresponding longitudinal (LO) phonons above 500–600 cm–1 were observed, which identify the formation of Co3O4 in the spinel structure. The study of optical absorption indicates the predominant existence in the films of phases with direct optical transitions. The optical band gap value was 1.43 and 1. 83 eV for Co3O4 and 2.65 eV for the cubic phase of CoO.

Исследование длинноволновых инфракрасных спектров отражения моно- и поликристаллов SmS в области гомогенности

The far- and mid-IR reflection spectra of Sm_1 + x S ( x = 0–0.17) samples are recorded and analyzed, as well as their electrical and structural parameters at a temperature of T = 300 K. The bond ionicity in SmS is shown to fall with a decrease in the area of the X-ray coherent scattering region and an increase in the concentration of donor impurities and, consequently, conduction electron concentration. The electrical conductivity of stoichiometric SmS single crystals and polycrystals can be determined with an error of 10% from the IR reflection spectra. Due to the low structural quality of the samples, the electrical conductivity cannot be determined in the case of deviation from stoichiometry.

SPECTRAL INVESTIGATIONS OF NANOCOMPOSITES ON THE BASIS OF POROUS SILICON

The results of experimental studies of porous silicon nanocomposites with biological materials: powder mineral phase of bone (hydroxyapatite) and biochemical solution identical to the natural tear fluid are presented in the work. Layers of porous silicon have been obtained in the process of electrochemical etching silicon wafers. There have been studies of IR reflection spectra of samples of nanocomposites in the range 4000-550 cm-1 produced.