V. I. Ivanov-Omskii

Modification of Hg1−xCdxTe properties by low-energy ions

We present an overview concerning the modification of properties of HgCdTe solid solutions and related Hg-containing materials under surface treatment with low-energy (60–2000 eV) ion beams. The conditions for conductivity-type conversion in p-material, dose, and time dependences of the depth of the conversion layer are analyzed. The modification of electrical properties of n-type material subjected to ion-beam treatment is discussed. The suggested mechanisms of conductivity-type conversion under low-energy ion treatment of HgCdTe doped with vacancies or acceptor impurities are regarded. Properties of p-n junctions produced by this technique are reviewed, and electrical and photoelectric parameters of HgCdTe IR photodetectors fabricated by low-energy ion treatment are analyzed. Several examples of novel device structures developed with the use of the method are presented.

Photoluminescence of Hg1 − xCdxTe based heterostructures grown by molecular-beam epitaxy

Photoluminescence (PL) of Hg1 − xCdxTe-based heterostructures grown by molecular-beam epitaxy (MBE) on GaAs and Si substrates has been studied. It is shown that a pronounced disruption of the long-range order in the crystal lattice is characteristic of structures of this kind. It is demonstrated that the observed disordering is mostly due to the nonequilibrium nature of MBE and can be partly eliminated by postgrowth thermal annealing. Low-temperature spectra of epitaxial layers and structures with wide potential wells are dominated by the recombination peak of an exciton localized in density-of-states tails; the energy of this peak is substantially lower than the energy gap. In quantum-well (QW) structures at low temperatures, the main PL peak is due to carrier recombination between QW levels and the energy of the emitted photon is strictly determined by the effective (with the QW levels taken into account) energy gap.

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T3 in the case of Auger recombination.

Negative Luminescence and Devices Based on This Phenomenon

Recent publications concerned with infrared emitters whose electrical modulation results in absorption of radiation detected as negative luminescence are reviewed. The main properties of the devices based on this phenomenon are analyzed.

One-phonon Raman spectra of carbon in composite films prepared by modification of amorphous hydrogenated carbon by copper and cobalt

One-phonon visible-range Raman spectra of a-C: H〈Cu〉 and a-C: H〈Co〉 composite films with comparable metal and carbon contents were studied in the frequency region 1200–1700 cm−1 including the carbon sp2-bond vibrations. Broad bands G and D characteristic of unmodified a-C: H films, as well as some additional features, are observed experimentally in the spectra. By unfolding the spectra into Gaussian components, it was possible to follow the variation of Raman shifts and of contributions of individual components to the spectrum as a function of metal content and thermal annealing. The data obtained, complemented by available information on carbon sp2-coordinated systems, show that incorporation of Cu or Co favors growth and ordering of graphite-like nanoclusters in a-C: H, the effect being substantially stronger in the case of Co. It is shown that the process of metal-stimulated graphitization includes carbon bond breaking with the formation of short chainlike fragments and their linkage with the formation of aromatic-ring nanoclusters. A qualitatively similar sp2-structure rearrangement takes place under thermal annealing. For the Cu and Co concentrations studied, the linear dimensions La of graphite-like clusters are estimated to vary from ∼0.8 nm in unannealed a-C: H to ∼1.0 and ∼1.2 nm in annealed a-C: H〈Cu〉 and a-C: H〈Co〉, respectively. The number of aromatic rings in these clusters is approximately estimated to increase from 12 to 16 (for Cu) and 20 (for Co).

Optical observation of bonded and quasi-free hydrogen in diamond-like carbon

Abstract The technique of vacuum UV Raman spectroscopy is applied to diamond-like carbon (a-C:H) films in order to study the state of hydrogen non-bonded with host carbon atoms. Under resonant excitation, a series of Raman bands related to rotational levels of a stretched H2 molecule is observed. The data are used to estimate the parameters of the H2 molecule in a-C:H. A model of the reversible transfer of hydrogen between the molecular state and states bonded to carbon is discussed.

Raman Scattering and Far Infrared Reflection–Absorption Spectra of the Four‐Component Solid Solution ZnxCdyHg1−x—yTe

The Raman spectra for three compositions of Zn x Cd y Hg 1-x-y Te (ZMCT) solid solution were obtained at 300 K. The experimental method allowed us to observe TO-phonon lines. The comparison of the spectra for compositions with x = 0.02, y = 0.7 and x = 0.12, y = 0.17 shows the appearance of additional lines at 163 and 175 cm -1 besides two lines which are observed in the range 120 to 150 cm -1 . Far Infrared Reflection Spectra (FIRS) were obtained for five compositions. Theoretical models for three modes of the four-component solid solution were constructed for the interpretation of the FIRS spectra of ZMCT. We obtained good agreement between the results of RS and FIRS which allowed us to determine the LO- and TO-phonon frequencies for HgTe-, CdTe- and ZnTe-like lattices.

Analysis of size-distribution function of metallic nanoclusters in hydrogenated amorphous carbon matrix

A method is proposed for mathematical processing of TEM images of nanocomposites with a large amount of non-uniform noise. The approach is 2D spline filtering of the image using the values of average background intensity. The method has been applied to TEM images of amorphous carbon doped with copper. A size distribution function of copper clusters has been obtained which is in a good accordance with earlier data. A dependence of cluster-to-cluster distance on cluster size has been found. This dependence validates the hypothesis of fluctuation growth of the clusters at lower metal contents and their coalescence at higher contents.

Magnetotransport phenomena in multimode lattices

The phonon and electron subsystems in the quaternary solid solutions of (ZMCT) were studied by means of Raman scattering and magnetophonon resonance. The Raman spectra for several compositions confirm that the phonon spectra exhibit three-mode behaviour. The cluster mode has also been observed. Four kinds of LO phonon (with HgTe-like, CdTe-like and ZnTe-like sublattices and ZnTe clusters) participate in the electron-phonon interaction. Four types of one-phonon magnetophonon resonance and two types of magnetophonon resonance on the difference of phonon frequencies have been observed. The peculiarities of the electron transport in these lattices are discussed.

Optical properties of amorphous carbon films deposited by magnetron sputtering of graphite

The thermal stability of amorphous carbon (a-C and a-C:H) has been studied by ellipsometry and spectrophotometry in the visible and near-UV range (1.5–5.6 eV). The dielectric function of amorphous carbon has been derived and analyzed using the Kramers-Kronig technique. The conventional analytical approach is shown to be insufficient for the analysis of thermally treated samples. The fundamental absorption edge is analyzed with respect to collective effects in nanoscale fragments of the graphite-like component of the amorphous carbon structure. Two types of graphite-like clusters contributing to the spectral dependence of the fundamental absorption edge and modified by thermal treatment are revealed.