Electrophysical properties of epitaxial gallium arsenide doped with acceptor impurities

Epitaxial layers of gallium arsenide doped with zinc and cadmium were grown in a chloride vapor-transport system using diethylzinc and dimethylcadmium as the sources of the impurity. We studied the effect of the inlet pressure of the impurities and the growth temperature on the doping level of the layers. We investigated the temperature dependences of the hole concentration and mobility in layers doped with zinc and cadmium up to different levels.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 54–58, February, 1995.     

Electrophysical characteristics of epitaxial cadmium telluride films

Equilibrium electrophysical characteristics of epitaxial CdTe films grown by the thermal screen method and the quasiclosed volume method are investigated. It is established that the films in both cases are semiconductors with inhomogeneous potential relief of the band to whose formation the main contribution is from barriers on the boundaries of the growth patterns. It is shown that jump conductivity with a variable jump length due to inhomogeneity of the potential relief of the bands and the high states density at the Fermi level is observed in CdTe films synthesized by the quasiclosed volume method for relatively high temperatures.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 72–76, March, 1990.     

Electrophysical properties of epitaxial layers of solid solutions of lead and tin tellurides doped with cadmium

Epitaxial layers of Pb_1−xSn_xTe (x≈0.2), undoped and doped with cadmium, are grown in a quasi-closed volume using the hot-wall method on BaF₂ fragments. The doping impurity is introduced directly into the material of the vapor source before synthesis in an equi-atom ratio with additional tellurium. The boundary of the limit of homogeneity from the side of the metallic components and in the region of the stoichiometric composition of the epitaxial layers doped with cadmium and the undoped epitaxial layers is established. The electrical conductivity and the Hall effect are investigated in the 77–450 K temperature range, and the temperature dependences of the intrinsic concentrations and of the ratio of the electron and hole mobilities are established. The temperature dependence of the Hall mobility is also investigated. The stability of the electrical parameters of the epitaxial layers are studied. It is shown that doping with cadmium enables highly stable n-type epitaxial layers to be obtained. Chernovits Branch, Institute of Problems of the Study of Materials, Academy of Sciences of Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 59–64, July, 1996.     

Electrophysical properties of dielectric films in MDM-structures

Using the methods of reactive cathode sputtering in a low-voltage, penning-discharge installation, dielectric films from silica, silicon nitride, aluminum nitride, etc. are obtained. Parameters of the films in MDM structures, their optical properties and porosity are investigated as a function of the deposition rate, substrate temperature and reaction gas pressure. It is found out that the films from silicon nitride exhibit the highest dielectric strength and those from silicon dioxide show the least dielectric loss.     

Photoelectric phenomena and photoluminescence in epitaxial CdSe thin films

Photoelectric phenomena and photoluminescence (static characteristics) were studied in epitaxial CdSe thin films built up on sapphire and fluorite substrates in a feedthrough CdSe-H₂ gas-transport system. It has been established that the spectral pattern of the extrinsic luminescence and photosensitivity in epitaxial films is determined by the common centers E_V+0.06, E_V+0.27, e_v+0.48 and E_V+0.60 eV. The presence of such centers also explains the trends which the temperature characteristics of the photocurrent follow, the spectral pattern of infrared quenching, and the lux-ampere characteristics of these films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 61–66, March, 1975.     

Spectral and luminescence properties of gadolinium gallium garnet epitaxial films doped with terbium

Gadolinium gallium garnet single-crystal films containing terbium are grown through liquid-phase epitaxy from a supercooled solution melt in the PbO-B₂O₃ system. The optical absorption spectra in the wavelength range 0.2–10.0 μm and the luminescence spectra excited by synchrotron radiation with energies in the range 3.5–30.0 eV are investigated at temperatures of 10 and 300 K. It is revealed that the optical absorption spectra contain an absorption band with the maximum at a wavelength λ ≈0.260 μm, which corresponds to the spin-allowed electric dipole transition between the electronic configurations 4f ⁸(⁷ F ₆) → 4f ⁷(⁸ S)5d of the Tb³⁺ ions. The narrow low-intensity absorption bands attributed to the 4f → 4f transitions from the ⁷ F ₆ ground level to the ⁷ F _0–5 multiplet levels of the Tb³⁺ ions are observed in the wavelength range 1.7–10.0 μm. In the luminescence spectra measured at a temperature of 10 K, the highest intensity is observed for a band with the maximum at a wavelength λ ≈ 0.544 μm, which is associated with the ⁵ D ₄ → ⁷ F ₅ radiative transition in the Tb³⁺ ion.     

Growth,electronic and magnetic properties of doped ZnO epitaxial and nanocrystalline films

We have used oxygen plasma assisted metal organic chemical vapor deposition along with wet chemical synthesis and spin coating to prepare Co_xZn_1-xO and Mn_xZn_1-xO epitaxial and nanoparticle films. Co(II) and Mn(II) substitute for Zn(II) in the wurtzite lattice in materials synthesized by both methods. Room-temperature ferromagnetism in epitaxial Co:ZnO films can be reversibly activated by diffusing in Zn, which occupies interstitial sites and makes the material n-type. O-capped Co:ZnO nanoparticles, which are paramagnetic as grown, become ferromagnetic upon being spin coated in air at elevated temperature. Likewise, spin-coated N-capped Mn:ZnO nanoparticle films also exhibit room-temperature ferromagnetism. However, the inverse systems, N-capped Co:ZnO and O-capped Mn:ZnO, are entirely paramagnetic when spin coated into films in the same way. Analysis of optical absorption spectra reveals that the resonances Co(I)↔Co(II)+e^- _CB and Mn(III)↔Mn(II)+h⁺ _VB are energetically favorable, consistent with strong hybridization of Co (Mn) with the conduction (valence) band of ZnO. In contrast, the resonances Mn(I)↔Mn(II)+e^- _CB and Co(III)↔Co(II)+h⁺ _VB are not energetically favorable. These results strongly suggest that the observed ferromagnetism in Co:ZnO (Mn:ZnO) is mediated by electrons (holes). PACS 75.50.Pp     

Electrophysical properties and energetical spectrum of heteroepitaxial germanium films

An epitaxial growth of Ge films from molecular beam is characterized by thermodynamical nonequilibrium. This leads to formation of numerous structural defects connected with local levels in the band gap (mainly acceptor-type). Depending on the deposition temperature the density of such levels may change in wide range (10¹⁶–10¹⁸ cm^?3). This determines various mechanisms of impurity conduction. The tails of the density of states in the band gap are also connected with the defect structure of the films. Stresses in heteroepitaxial Ge films result in the splitting of the valence band atk = 0 and in a change of the band gap. Thus, these stresses have influence on the electrical and optical properties of the films.     

Electrophysical properties of zinc-sulfide films obtained by high-frequency magnetron sputtering

The structure and electrophysical properties of zinc-sulfide films obtained by high-frequency magnetron sputtering are investigated. It is shown that the electrical strength of the films is no less than 10⁶ V·cnr^–1, the width of the forbidden band is 3.2–3.3 eV, and the refractive index is 1.8. The films are tested as electroluminescent layers in thin-film electroluminescent emitters. Luminescence with a brightness of 150 cd/m² is obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 29–32, June, 1990.It remains to thank A. A. Miller for perfecting the electron-microscope investigations.     

Strain-induced properties of epitaxial VOx thin films

We have grown VOx thin films on different substrates in order to investigate the influence of epitaxial strain on the transport properties. We found that the electric conductivity is much larger for films grown under compressive strain on SrTiO3 substrates, as compared to bulk material and VOx films grown under tensile strain on MgO substrates. A clear crossover from metallic to semiconducting behavior is observed when increasing the oxygen content x. Apparently, the application of strain induces a Mott-Hubbard insulator-to-metal transition in VOx<1. The VOx/SrTiO3 films show an unexpected large positive magnetoresistance effect at low temperatures, which is not found in the VOx films grown under tensile strain on MgO or on a substrate with a similar lattice parameter.     

Electrical properties of epitaxial magnesium-manganese-zinc ferrite films

The resistivity of Mg-Mn-Zn ferrite films from 2.4 to 12 μ thick was studied as a function of the temperature during cyclic heating from 20 to 450 °C and subsequent cooling. The resistivity and activation energy were found as functions of the film thickness. A study was made of the effect of annealing in air on the resistivity, activation energy, exchange-interaction parameter, saturation magnetization, and domain structure of the Mg-Mn-Zn ferrite films.     

Electrophysical properties of MIS structures with nanodimensional β-cyclodextrin Langmuir-Blodgett films

Mixed cyclodextrin-phenanthrene monolayers at the water-air interface are studied. The formation conditions for Langmuir-Blodgett films on single-crystalline substrates are found. Aluminum/Langmuir-Blodgett film/single-crystal n-Si structures are obtained, and their properties are investigated by taking current-voltage and lux-ampere characteristics. The deposition conditions of the Langmuir-Blodgett film and its thickness are shown to influence the electrophysical and photoelectric properties of the heterostructures.     

Electrophysical properties of anode oxide films on an indium antimonide surface

Anode oxide films are widely used for the passivation of the surface of semiconductors of group A^IIIB^V (GaAs [1–5], InSb [6–8], InAs [9], etc.) and as a subgate dielectric in MOS devices on a base of these materials. As well as a study of the properties of the boundary of separation of an anode oxide-semiconductor, the investigation of the electrophysical properties of such anode oxide films is an independent and extremely important problem. This is due to the fact that such characteristics of MOS devices as the charge stability, hysteresis phenomena, leakage currents through the gate, etc., are largely determined by the volume properties of the dielectric layer (by the spectrum of localized electron states in the volume, the mechanism of charge transfer through the dielectric film, etc.). At the same time, much less attention has been paid to the study of the properties of anode oxide films than to the investigations of the boundary of separation of a dielectric and a semiconductor. In this paper we investigate the electrophysical properties of anode oxide films of indium antimonide obtained by anode oxidation of a semiconductor substrate in a 0.1 N aqueous solution of KOH. We measured the dependence of the capacitance of the anode oxide on frequency (f), on temperature (T), and on the bias voltage (V), as well as the DC current-voltage characteristics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 79–83, April, 1981.     

Hole mobility and trapping in PVK films doped with CdSe/CdS and CdSe quantum dots

Experimental study of the hole mobility in polyvinylcarbazole (PVK) films doped with two kinds of nanocrystals, on bare core CdSe and core-shell CdSe/CdS quantum dots, with concentrations ranging from 3 · 10¹⁰ to 3 · 10¹⁵ cm⁻³, is presented. The quantum dots investigated were made using colloidal chemistry. The hole mobility was measured using the time-of-flight technique as a function of the applied electrical field in the range 10⁵–10⁶ V/cm and for temperatures from 20°C to 50°C. The transient curves, being featureless on a linear plot, show on a double logarithmic scale a sharp inflection point indicating a dispersive carrier drift process. The recovered values of the mobility are in the range 3 · 10⁻⁸–10⁻⁶ cm²·V⁻¹·s⁻¹ and their field and temperature dependences can be analyzed formally within the framework of the Gaussian disorder model proposed by B?ssler. The energetic disorder is, within the experimental accuracy, independent of the concentration and type of quantum dots for the CdSe quantum dots at all concentrations and for the CdS/CdSe quantum dots up to 10¹⁴ cm⁻³. The spatial disorder factors are very large (from 5.3 to 8.7) and do not depend in a systematic way upon the type and concentration of quantum dots (QDs). The experiments show that the apparent mobility does not change considerably with concentration, but it was found that the samples with CdSe/CdS quantum dots at concentrations from 10¹⁵ to 3 · 10¹⁵ cm⁻³ show a decreased photocurrent response. The dependence of the time-integrated transients (corresponding to the full charge value) upon the quantum-dot concentration has been determined. Differences in total photogenerated charge for pure and doped polymer films imply that the quantum dots of that type are the hole traps with capture times much more smaller than the transit time and with emission times a few orders longer than the transit time. CdSe quantum dots without a shell do not seem to exhibit the same properties as core shells and do not produce considerable changes in the charge transfer, even at a density of 10¹⁵ cm⁻³.     

CdSe epitaxial films and nanostructures grown by the isothermal closed space sublimation technique

The use of the isothermal closed space sublimation technique for growing CdSe very thin films and nanostructures is reported. In this technique, the samples are grown by exposing a substrate alternately to elemental sources of Cd and Se. The whole system is at the same temperature, so the only driving force for the film growth is the vapour pressure difference between the elemental source and the film surface. This is due to the difference in chemical potential between the pure elements and the elements when forming the compound. Between subsequent exposures the surface is exposed to the carrier vapour. In this step, re-evaporation of the non-stable outermost part of the films can be controlled. This procedure leads to a self-regulated growth rate in which the size of the deposited materials is controlled very accurately. In this way, nanostructures and epitaxial thin films of CdSe were grown on single-crystal substrates. For the nanostructure growth a nanoporous anodic alumina membrane (AAM) was interposed between the elemental sources and the substrate. Optical and structural properties of the structures are reported. The structural characterization using x-ray diffraction and high resolution electron microscopy reveals the epitaxial quality of the films and the chemical composition and morphology of the semiconductor filled AAM samples.     

Electro-optical properties of doped anthracene films

Electroluminescence in anthracene doped with anthraquinone (10^?3 mole%) films are presented. Films are deposited at room temperature in a vacuum of 10^?5 torr. It is observed that at constant frequency the brightness/voltage relationship follows the relation $\text{B = B}{}_0\text{exp}\text{(?b/V}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}$. The results show that electroluminescent brightness increases linearly with frequency. At lower frequencies green electroluminescent (EL) emission and at higher frequencies blue EL emission is observed. Similar nature for I–V and brightness/voltage relationship are found in anthracene doped with 10^?4 mole% anthraquinone.     

Optical properties of BiFeO3 epitaxial thin films

The properties of neodymium-doped BiFeO₃ nanosized films on magnesium oxide single-crystal substrates are studied. The films are obtained using high-frequency sputtering with the aid of layered growth. The structural perfection of the films is analyzed using the X-ray diffraction. The transmission of the films with different thicknesses is studied in the wavelength interval 200–1100 nm. The spectra are processed with the aid of a dispersion formula for permittivity of a sum of oscillators with allowance for damping, so that direct and indirect transitions can be revealed. The absorption edges are estimated to be 2.81 and 2.78 eV for the direct transitions of the films with thicknesses of 14 and 60 nm, respectively.     

Preparation and properties of epitaxial ZnGeP2 films

Thermodynamic analysis has been applied to the vapor over a ZnGeP₂ crystal when the chlorine source is provided by ZnCl₂. ZnGeP₂ film growth has been examined and the electrophysical and photoluminescence parameters have been measured. All these autoepitaxial films have the chalcopyrite structure, while those parameters are determined by the defects and the substrate orientation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 74–78, April, 1988.We are indebted to L. G. Lavrent'eva for interest, to A. I. Gribenyukov and T. E. Tkachenko for assistance in growing the single crystal; and to F. Kim for the microprobe analysis.