V. G. Klyuev

Luminescence and photoconductivity of alkali-metal-doped cadmium sulfide films

Data are presented on the luminescence and photosensitivity of cadmium sulfide films doped with an alkali metal (Na or K) in the presence of chlorine. The doping is shown to increase the luminescence quantum yield by more than one order of magnitude in comparison with undoped CdS films. The doped films are resistant to high-intensity UV radiation, which usually initiates photochemical reactions.

Recombination processes in pyrolytic cadmium sulfide films

The study concerns the photoelectric properties of pyrolytic CdS films, both undoped and doped with alkali metals. It is established that the films exhibit a long relaxation time of the photoconductivity at room temperature (t = 103−104 s). The long relaxation is due to internal potential barriers between regions different in conductivity. The activation energy of the stored-up conductivity is determined at E = 0.68 eV. By thermostimulated conductivity studies of the films, three types of electron localization levels are found. These are related to sulfur vacancies (0.48 eV), oxygen substituting for sulfur (0.5 eV), and adsorbed alkali metal atoms (0.53 eV). On the basis of the results of studies of recombination processes, the model of energy levels in the band gap of pyrolytic CdS films doped with alkali metals is developed.

Relationship between structural and optical properties of colloidal CdxZn1−xS quantum dots in gelatin

Abstract. Aqueous synthesis of mixed cadmium and zinc sulfides colloidal quantum dots (QDs) has been successfully realized. Colloidal CdxZn1−xS QDs are formed in a cubic crystal lattice with particle size of ∼2  nm. The blueshift of optical absorption spectra from 420 to 295 nm and recombination photoluminescence from 646 to 483 nm with increasing zinc content in QDs was observed. Optimum photoluminescence intensity occurs for QDs with Cd0.3Zn0.7S composition. With increasing zinc content up to Cd0.3Zn0.7S, luminescence intensity increases and decreases when zinc content is larger than 0.7. The increase in photoluminescence intensity is explained by the increase in the number of point defects, such as complexes of interstitial metal atoms–metal vacancies [Mei−VMe]. Such complexes occur due to displacement of the metal atom at the center of the elementary tetrahedron due to substitution of one of the four sulfur atoms by an impurity atom, such as an oxygen atom.

Photoconductivity of CdS films, undoped and doped with alkali-metal impurity ions

The nonequilibrium electron processes that occur during photoconductivity increase and relaxation in pyrolytic CdS films, both nominally undoped and doped with alkali metals, are studied. The photocurrent increase and relaxation are slow. In some cases, the experimental curve describing the photoconductivity increase is S-shaped or exhibits several thresholds. The dependence of the steady-state photocurrent on the excitation intensity is superlinear. The introduction of alkali-metal impurities increases the photocurrent in the CdS films by up to an order of magnitude compared to the photocurrent in the undoped films. The experimentally observed features of the photoconductivity kinetics of the structures under study are attributed to the profound effect of trapping centers of several types on the behavior of nonequilibrium charge carriers.

New method for measuring the IR surface impedance of metals

A method for measuring the IR optical properties of metals, which implies the analysis of the angular distribution of the photons emitted from the edge of a metal plate due to the conversion of thermal surface plasmons, has been theoretically and experimentally shown. In this work an increased accuracy of the proposed method in the IR region is demonstrated in comparison with more conventional methods based on the Fresnel formulas. This conclusion is supported experimentally with data obtained from the surface impedance measurement of copper in the range from 8 to 9 μm at 185°C.

Photostimulated Luminescence Flash: from Scientific Photography to Photonics of Nanostructured Materials

We have analyzed the possibilities of using the phenomenon of photostimulated luminescence flash for optical diagnosing of energy levels of structural and impurity defects of semiconductor crystals and nanostructures. New data on the spectra of deep localized states associated with adsorbed few-atom clusters Znn on the surface of ZnS; clusters Cdn, Cun, and Agn on the surface of CdS; and clusters Agn on the surface of AgBr(I) have been presented, as well as results of investigation of photostimulated assembling processes of few-atom clusters on the surface of crystals using this phenomenon. We are the first to show the potential of the luminescence flash technique for studying the mutual arrangement of the levels of dye molecules and the bands of the crystal on the surface of which they are adsorbed, as well as of the spectra of localized states in colloidal CdS semiconductor quantum dots.

A Method for Determining the Ionization Spectra of Monodispersed Clusters of Noble Metals Adsorbed on the Surfaces of Ionic–Covalent Crystals

The method described is based on the vacuum deposition of separate monodispersed molecular metal ions from a mass-separated beam on the surfaces of ionic–covalent crystals and the detection of ultralow concentrations (108 cm–2) of adsorbed states using the method of photostimulated luminescence flash.

Photoelectric properties of CdS films with nanostructured surfaces

The results from studying the photoelectric properties of CdS films with nanostructured surfaces and synthesized via pyrolysis of thiourea coordination compounds are presented. It is shown that the photocurrent limiting effect is observed in the studied structures at higher intensities of the excitation light. This effect, which is attributable to the optical smoothing of nonuniform barrier relief, could find practical application in optoelectronics.

Crystalline and optical properties of Cd x Zn 1– x S (0.5 ≤ x ≤ 1) films doped with silver

The results from studying CdxZn1–xS (0.5 ≤ x ≤ 1) films fabricated via pyrolysis from thiourea coordination compounds of cadmium and zinc bromides doped with silver ions having impurity concentrations of 10–7, 10–6, 10–5, 10–4, and 10–3 mol L–1 in sputtered solutions are presented. Films prepared at 400°С have the wurtzite lattice. The bandgap of pure and doped films, determined from absorption spectra near the edge of fundamental absorption, varies linearly from 2.5 to 3.11 eV. An order of magnitude increase in the intensity of luminescence is observed after doping with silver.

Luminescence and optical properties of Cd0.9Zn0.1S films doped with copper

Results from investigating Cd0.9Zn0.1S films prepared via spray pyrolysis using thiourea coordination compounds [Cd(N2H4CS)2Br2] and [Zn(N2H4CS)2Br2], doped with copper ions in concentrations of 10−7–10−4 at %, are presented. The crystal structure of the films is investigated. The films’ optical band gap widths are 2.63–2.68 eV. The intensity of photoluminescence increases for the films doped with ions of copper.