L. Yu. Zakharov

Optical properties of Si nanocrystals prepared by magnetron sputtering

Visible photoluminescence (PL), optical transmission, and Raman scattering spectra of Si nanocrystals embedded in SiO2 matrix have been studied. Films were deposited by rf magnetron sputtering of compound SiO2/Si targets. Films containing silicon in the form of nanocrystals clusters show intense luminescence at room temperature. Films containing only amorphous Si clusters show little or no PL. Annealing in vacuum or in specific atmosphere leads to strong change of the PL spectrum and its intensity. Results are explained by strong influence of the Si/SiO2 interface state on integral PL emission.

Deposition of heteroepitaxial layers of topological insulator Bi2Se3 in the trimethylbismuth–isopropylselenide–hydrogen system on the (0001) Al2O3 and (100) GaAs substrates

Thin solid layers that are formed upon heating of the gaseous trimethylbismuth–isopropylselenide–hydrogen system on the (0001) Al2O3 and singular and vicinal (100) GaAs surfaces are studied. The conditions for deposition of metal Bi and phases of Bi4Se3, BiSe, and topological insulator Bi2Se3 using the MOCVD method are determined. Pure metastable phase BiSe is obtained for the first time. Bi2Se3 films with a thickness of no less than 200 nm, a relatively low volume concentration of 3 ×1018 cm–3, and a high mobility of carriers at 300 K (1000 cm2 V–1 s–1) are fabricated.

Metal-semiconductor-metal photodiodes based on ZnCdS/GaP wide-gap heterostructures

Good epitaxial ZnCdS layers are grown on GaP semiconductor substrates by metal-organic chemical vapor deposition. The respective photodiode structures are fabricated by the metal-semiconductor-metal method, and their characteristics are studied. The diodes feature low dark currents. The bias dependence of the spectral response of the detector is determined. The long-wavelength edge of the ZnCdS/GaP diodes shifts from 355 to 440 nm as the bias voltage varies from 40 to 80 V. At the maximal photosensitivity wavelength (355 nm), the ampere/watt sensitivity of the detector is 0.1 A/W.

SPECTRAL ELLIPSOMETRY OF MULTILAYER ZnS/ZnSe HETEROSTRUCTURES

By the method of spectral ellipsometry with binary modulation of the polarization state the dispersions of the refractive index n, absorption coefficient k, and layer thickness in ZnS/ZnSe multilayer structures grown by the chemical gas‐phase deposition method from heteroorganic compounds on GaGaAs‐substrates with ZnSe buffer layers have been determined. The efficiency of local ellipsometric measurements (with a light beam size less than 150 × 500 μm) permitting mapping of the parameters of structures with A2B6 layers up to a few microns thick has been demonstrated. The optical properties of oxide layers formed on the zinc selenide surface have been investigated. Multilayer structures (ZnSe/ZnS)n/ZnSe/GaAs with a pronounced exciton absorption and specific features in the reflection spectra coinciding in energy with exciton transitions, as well as Bragg mirrors with a reflection coefficient up to 99% in the blue region of the spectrum, have been studied.

MSM optical detector on the basis of II-type ZnSe/ZnTe superlattice

On the basis of a type-II ZnSe/ZnTe superlattice, a MSM (metal—semiconductor–metal) photodetector is fabricated and investigated. The detector features low dark currents and a high sensitivity. The spectral characteristic of the detector provides the possibility of the selective detection of three separate spectral portions of visible and near-infrared radiation.

An ultraviolet MSM photodetector with electrically tunable spectral sensitivity

Ultraviolet photodetectors based on interdigital Schottky-barrier contacts to a ZnCdS/GaP heterostructure, which have low dark currents, are fabricated and investigated. It is found that the characteristics of the spectral response of these detectors depend on the bias and the long-wavelength boundary of the response of a ZnCdS/GaP metal-semiconductor-metal (MSM) diode can be shifted from 355 nm to 440 nm as the bias varies from 40 to 80 V. It is found that, at the wavelength of the maximum photosensitivity (355 nm), the ampere-watt sensitivity of the detector is 0.1 A/W.

Selective UV radiation detection on the basis of low-dimensional ZnCdS/ZnMgS/GaP and ZnCdS/ZnS/GaP heterostructures

The detecting properties of periodic heterostructures with ZnCdS quantum wells separated by ZnMgS or ZnS barrier layers are studied. Heterostructures are grown on semi-insulating GaP substrates by metal organic vapor-phase epitaxy (MOVPE). On their basis, metal–semiconductor–metal (MSM) diodes with interdigital Schottky contacts 3 μm, distances between them of 3 μm, and a total detector area of 100 × 100 μm are fabricated. The detectors have low dark currents (10–12 A); at low bias voltages, they provide a narrow- band response (full-width at half-maximum of FWHM = 18 nm at a wavelength of 350 nm) which is controlled by the ZnCdS quantum-well composition. As bias is increased to 70 V, the maximum detector sensitivity shifts by a wavelength of 450 nm, which is caused by penetration of the external-bias electric field into the semi-insulating GaP substrate. In this case, the narrow-band response of the detector at a wavelength of 350 nm is retained, i.e., the two-color detection of light is provided.

Nature and spatial localization of electroluminescence sources in the metal-composite layer-semiconductor structures

Variations in the electroluminescence spectra and intensity of the metal-composite layer-semiconductor (Au-SiOxNy(Si)-cSi) structures as functions of the characteristics of the luminescent-active transition region at the interface of the cSi substrate and the SiOxNy(Si) composite layer are studied. New information on localization of the electroluminescence sources in the transition region is obtained. It is found that the transition region contains various luminescence-active silicon inclusions, which contribute to both the short-wavelength (λ ≈ 500–1000 nm) and long-wavelength (λ ≈ 1000–1600 nm) branches of electroluminescence. The effect of technological factors on the electroluminescence spectra, intensity, and quantum efficiency is analyzed.

Electroluminescence mechanisms in SiO x N y (Si) nanocomposite films

With a view to creating the Si LED, the mechanisms of electroluminescence (EL) in SiOxNy(Si) nanocomposite films with Si nanocrystals embedded in the SiOxNy matrix are studied experimentally and theoretically. The most important results are obtained from a Au/SiOxNySi)/p-Si structure having a semitransparent electrode, the oxynitride film containing Si nanocrystals with a mean size of 3–5 nm and a concentration of ∼1018 cm−3; the measurements are made on a reverse-biased structure (substrate potential negative). Room-temperature EL is observed in the visible and IR ranges; the respective peaks are located at wavelengths of 600–700 and about 1200 nm. The study examines current-voltage characteristics of the structure and the dependence of integrated EL intensity on current, voltage, film thickness, the type of substrate conductivity, etc. The following conclusions are drawn from the experimental and theoretical results: The IR branch is mainly associated with carrier heating, avalanche ionization, and formation of light-emitting microplasmas near the substrate-film interface. The visible branch is linked to (i) hot-electron injection from the substrate into the film and (ii) impact excitation of luminescent centers at nanocrystal-matrix interfaces.

Photo-MOVPE growth and characterization of ZnSeZnxCd1 − xSe heterostructures

Abstract We have studied the growth of ZnCdSe layers on (1 0 0) GaAs substrates using atmospheric metalorganic vapor phase epitaxy (MOVPE). It was found that surface fluctuations of temperature were the main reason for compositional non-uniformity. The photo-assisted technique and a mechanism for rotational and back and forth movement of the substrates have been used for the growth of the Zn 0.45 Cd 0.55 Se- and CdSe-based heterostructures giving good homogeneity of the width and composition on a 12 cm 2 area at growth temperatures as low as 400–425°C. Strained single Zn 0.45 Cd 0.55 Se layers embedded in a ZnSe matrix were pseudomorphic up to the thickness of 4.5 nm. Strong green emission from a single well and 50 periodic Zn 0.45 Cd 0.55 Se ZnSe superlattices (SL) are observed under 441.6 nm HeCd laser excitation at 77 K.