P.I. Kuznetsov

Superlattice ZnSxSe1−x/ZnSySe1−y on (100) GaAs obtained by a photoassistant metal-organic chemical vapour deposition method

Abstract The influence of radiation in the visible spectral range on the growth rate and composition of ZnSxSe1−x during the usual metal-organic chemical vapour deposition process was observed. This fact was used to grow the superlattice under pulse radiation from a xenon or tungsten lamp directed at a GaAs substrate. Superlattices with periods of 60–1500 A were obtained by this method.

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.

Ultrathin CdSe quantum wells

Abstract We report a survey of samples containing ultrathin layers of CdSe embedded in ZnSe or ZnS0.06Se0.94 matrices. CdSe single quantum wells (SQW) with well widths in the range 0.3–3 ML show several bands in the photon energy range from 1.7 to 2.4 eV. Similar bands have been attributed recently to self-organised quantum dots. Temperature-dependent photoluminescence (PL) shows that the bands in our samples vanish, without significant peak shift, at moderately high temperatures. Preliminary time-resolved PL shows that they also have relatively long lifetimes (ca. 30−250 ns). In all samples, the SQW exciton band lying at higher energies shows line narrowing with increasing temperature. Variations due to quantum-well thickness induce a correlation between the luminescence peak energy and the optical bandwidth which may be used to systematise our observations.

A bicolor photodetector of ultraviolet radiation based on a low-dimensional ZnCdS/ZnMgS/GaP heterostructure

A bicolor photodetector of ultraviolet radiation based on a ZnCdS/ZnMgS/GaP heterostructure is designed and analyzed. At low bias voltages, the detector has a narrowband response at a wavelength of 350 nm, which is determined by the composition of the ZnCdS quantum well. As the bias increases to 80–100 V, the maximum sensitivity of the detector is shifted to a wavelength of 450 nm with subsequent rapid decrease. In this case, the spectral sensitivity characteristic of the detector covers the region of the maximum pigmentation effect of solar 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.

A polarization analyzer of optical radiation on the basis of the light diffraction by sound

A device with an acousto-optic polarization splitter as the basic unit has been developed to record polarization-modulated optical signals. It spatially separates input radiation into two beams with mutually orthogonal polarizations. The difference of their intensities serves as the measure of changes in the input-radiation polarization plane. Experiments were performed using a TeO2 single crystal as the acousto-optic splitter and showed the high efficiency of splitting optical radiation with a wavelength of 0.63 μm in the range of acoustic frequencies of 10–26 MHz.

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.

Excitons in ZnSe1 − xSxZnSe1 − ySy superlattices grown by photomodulated MOCVD

Abstract The superlattices ZnSe 1 − x S x ZnSe 1 − x S y of alternating layers of solid solutions differing in composition were grown by photomodulated MOCVD method. A high quality of our samples was evidenced by the sharp exciton spectra and high intensity of exciton luminescence. The analysis of the band shapes of 1LO and 2LO exciton replica shows that the excitons in our SLs can be considered as free particles with the equilibrium kinetic energy distribution. The exciton motion in the studied SLs has essentially three-dimensional character due to the small height of the barriers. However, the periodic potential of SL perturbs the exciton wave vector, introducing additional elastic exciton scattering which can be detected through the band-shapes of phonon-assisted exciton luminescence.