Spectral shift of photoluminescence bands of the (SiC)1−x (AlN)x epitaxial films due to laser annealing

The effect of laser annealing on the photoluminescence properties of (SiC)_1?x (AlN)_x epitaxial films was studied. It was proposed that annealing causes the displacement of the Al and N atoms from their lattice sites and the formation of Al_Si-N_C donor-acceptor pairs acting as the luminescence centers. According to this model, the increase in the annealing time is accompanied by the formation of donor-acceptor pairs with the shortest interatomic distances at the expense of associations of the distant defects and by a shift of the respective photoluminescence band to the high-energy spectral region.     

Possibility of obtaining the (GaSb)1 − x (Si2) x films on silicon substrates by the method of liquid-phase epitaxy

Semiconductors - It is shown that it is possible to grow a continuous series of (GaSb)1 ? x (Si2) x (x = 0?1) alloys on silicon substrates by the method of liquid-phase epitaxy from a...     

Effect of annealing on the electrical properties of Pb1 − x Mn x Te single crystals with excess tellurium

The electrical conductivity σ, Hall coefficients R, and thermopower α of Pb_0.96Mn_0.04Te (Te) single crystals annealed at 573 K for 120 h are investigated. It is shown that, in contrast to unannealed samples, the investigated samples exhibit n-type conductivity and metal-type dependences σ(T) in the temperature range 77–300 K. It is suggested that, upon annealing, a portion of the excess tellurium atoms occupy vacancies in the lead sublattice with the formation of new vacancies in the tellurium sublattice of the samples.     

Ellipsometric study of ultrathin AlxGa1−x As layers

A method for rapid monitoring of the parameters of thin-layer semiconductor structures by ellipsometry is proposed. The results of ellipsometric analysis of the material thickness and composition distribution in Al_xGa_1?x As films grown by low-temperature liquid-phase epitaxy (LPE) are presented. The ellipsometric data are compared to those obtained by the Raman scattering spectroscopy.     

Internal microstrain and distribution of composition and cathodoluminescence over lapped AlxGa1−x N epilayers on sapphire

Structural properties and spatial inhomogeneity of MOCVD-grown Al_xGa_1?x N layers on (0001) sapphire substrates were studied. A nonuniform distribution of Al across the epilayer was observed in layers grown at constant flux rates of precursors. The model of compositionally graded layer formation is proposed on the basis of cathodoluminescence and X-ray data. It is established that homogeneous samples can be obtained by increasing the flux rate of trimethylaluminum at the initial stage of epilayer growth compared with that in all further stages. Lowering the growth rate reduces strain in epitaxial Al_xGa_1?x N layers. The influence of strain on the luminescence properties of the layers is discussed.     

Synthesis of compositionally different multicomponent metal-oxide films (SnO2) x (ZnO)1 − x (x = 1–0.5)

The study is concerned with high-purity SnO₂ and ZnO powders produced from salt solutions of corresponding metals by low-temperature hydrothermal synthesis. Fragments of SnO₂ and ZnO ceramic targets formed as 1 × 8 cm bars are fabricated by dry pressing. The bars are used to form composite targets for ion-beam sputtering and the fabrication of compositionally different (SnO₂) _x (ZnO)_{1 ? x} (x = 1–0.5) films appropriate for the production of gas sensors or transparent electronic devices. The optical and electrical parameters of the films with different compositions are studied.     

Cadmium(1−x)zinc(x)telluride thin films deposited by sequential pulsed laser deposition

In this work, sequential pulsed laser deposition was used for the deposition of cadmium zinc telluride (CZT) thin films. CZT is a ternary II–VI compound semiconductor with a tunable band gap between 1.51 and 2.26 eV. In this work, three different CZT film compositions were achieved at room temperature by sequential deposition of nanometric layers with a precise number of laser shots on the cadmium telluride (CdTe) and zinc telluride (ZnTe) targets. XPS, XRD and UV–vis transmittance techniques were used to characterize the CZT films. The atomic content of zinc ranged from 60% down to 13%. This represents an enlargement of the lattice constant from 6.19 to 6.41 Å, and a band gap decrement from 1.94 to 1.55 eV. In addition, the CZT film resistivity can be modulated between the CdTe (4.1×10⁷ Ω-cm) and ZnTe (2.8×10⁵ Ω-cm) values. Our results demonstrated that the sequential pulsed laser deposition can be used to obtain several CZT film compositions with precise control of its stoichiometry and can be extended to the production of other ternary compounds.     

Mechanism of the current flow in Pd-(heavily doped p-AlxGa1−x N) ohmic contact

The physical mechanism of the current flow in Pd-(heavily doped p-Al_xGa_1?x N) ohmic contact is studied. Chloride-hydride epitaxy was used to grow the p-Al_0.06Ga_0.94N solid solution with uncompensated acceptor concentration N _a –N _d ranging from 3×10¹⁸ up to 10¹⁹ cm^?3. Thermal vacuum deposition and subsequent thermal treatment were used to form an ohmic Pd contact. It is shown that, after the thermal treatment, the Pd-p-Al_0.06Ga_0.94N barrier contact with a potential barrier height of about 2.3 V becomes ohmic and the barrier height decreases to approximately 0.05 V. For uncompensated acceptor concentration N _a –N _d =3×10¹⁸ cm^?3, thermionic emission is found to be the main mechanism of the current through the Pd-p-Al_0.06Ga_0.94N ohmic contact. An increase in N _a –N _d to approximately 10¹⁹ cm^?3 in the solid solution leads to a transition from thermionic emission (at high temperatures) to tunneling (at low temperatures).     

Photosensitivity of thin-film structures based on (CuInSe2)x(2ZnSe)1−x solid solutions

Polycrystalline (CuInSe₂)_x(2ZnSe)_1−x films (x=0.6–1.0) with p-type conductivity and a thickness of 0.5–0.9 μm were obtained by pulsed laser evaporation. It is shown that a chalcopyrite-sphalerite transition occurs in the above system for x=0.7. The obtained films were used to fabricate the photosensitive structure of the In/p-(CuInSe₂)_x(2ZnSe)_1−x and InSe(GaSe)/(CuInSe₂)_x(2ZnSe)_1−x types. Spectral dependences of photovoltaic-conversion quantum efficiency were studied, and the photosensitivity of the structures in relation to the type of energy barrier and the composition was analyzed. It is concluded that the structures under consideration can be used as broadband photovoltaic converters. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 5, 2000, pp. 576–581. Original Russian Text Copyright ? 2000 by V. Rud’, Yu. Rud’, Bekimbetov, Gremenok, Bodnar’, Rusak.     

Study of the recombination process at crystallite boundaries in CuIn1 − x Ga x Se2 (CIGS) films by microwave photoconductivity

The loss kinetics of photogenerated charge carriers in thin polycrystalline chalcopyrite CuIn_1?x Ga _x Se₂ (CIGS) films has been studied by microwave photoconductivity (at 36 GHz). The films were synthesized using the ampoule method and three variants of physical vapor deposition with subsequent selenization: magnetron sputtering, thermal deposition, and modified thermal deposition with intermetallic precursors. The photoconductivity was excited by 8-ns nitrogen laser pulses with maximum intensity of 4 × 10¹⁴ photons/cm per pulse. Measurements were performed in the temperature range 148–293 K. The photoresponse amplitude is found to depend linearly on the sizes of coherent-scattering regions in the film grains, which were calculated from X-ray diffraction data. The photoresponse decay obeys hyperbolic law. The photoresponse half-decay time increases with a decrease in both temperature and light intensity. It is shown that the recombination of free holes with trapped electrons is very efficient near the crystallite boundaries.     

Nonvolatile memory cells based on the effect of resistive switching in depth-graded ternary Hf x Al1 − x O y oxide films

A nonvolatile memory cell prototype based on the effect of resistive switching in thin Hf _x Al_{1 ? x} O _y oxide films grown by atomic layer deposition (ALD) with a Al depth-graded profile has been developed. This prototype imitates the arrangement of memory cells between the metallization layers of integral circuits. The obtained results are much superior to the parameters of conventional flash memory cells in increasing the reset speed and decreasing the reset voltage.     

Organometallic VPE growth of AlxGa1−xAs

The " hybrid" organometallic VPE process for the growth of Al_xGa_l-xAs has been explored. Six growth parameters have been considered; substrate orientation, substrate temperature during growth, total flow rate and ratios of Al, HC1 and As to the total group III flow rate. The effects of these six growth parameters on the growth process (growth rate, composition and surface morphology) and the materials properties (carrier concentration, photoluminescence intensity and spectrum) have been systematically studied. A technique has been developed for the growth of heterostructures by changing only the H₂ diluent flow rate. This results in high quality heterostructures with x changing from 0.05 to 0.30 in > 100 å.     

Phase formation upon the interaction of thin films in the system Yb1 − x Sm x Te-As2Te3

Phase formation upon the interaction of thin Yb_{1 ? x} Sm _x Te (x = 0.02) and As₂Te₃ films obtained through their simultaneous and successive evaporation is studied. It is shown that the Yb_{1 ? x} Sm _x As₄Te₇ phase is formed upon interaction of the thin films at a temperature of 473 K and the Yb_1?x Sm _x As₂Te₄ phase at 503 K.     

Dependence of surface morphology of CVD diamond films on deposition conditions

The diamond films have been deposited by the hot filament CVD method on molybdenum substrates from the mixture reactant gas of acetone and hy-drogen.The surface morphologies of the obtained diamond films under various de-position conditions have been observed by scanning electron microscope (SEM).The experimental results strongly indicate that the surface morphologies of the re-sulting films have closely related to the deposition conditions,i.e.,reaction pres-sure.For molybdenum substrates,under the lower reaction pressure the surface morphologies of the grains comprising the resulting films mainly display the small single crystal cubo-octahedron and double small crystal cubo-octahedron;under the higher reaction pressure ,the surface morphologies mainly display the large cauliflower-like .These results show that there are various crystal habits for CVD diamond under various deposition conditions .     

Dependence of surface morphology of CVD diamond films on deposition conditions

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Influence of cation-vacancy imperfection on the electrical and photoelectric properties of the Cu1 − x Zn x InS2 alloy

The growth technology of single crystals of Cu_{1 ? x} Zn _x InS₂ alloys (x = 0–12) of n-type conductivity is developed. The formation mechanism of the alloy is investigated by X-ray structural analysis. It is shown that the single crystals have chalcopyrite structure, and the unit-cell parameters depend on the alloy composition. The temperature dependence of the electrical conductivity in the temperature range T = 27–300 K and the spectral distribution of the photoconductivity at T ≈ 30 K are investigated. Induced photoconductivity is found for CuInS₂-ZnIn₂S₄ with a content of ～8 and ～12 mol % ZnIn₂S₄ and thermally stimulated currents are investigated.     

Effect of rapid thermal annealing on the parameters of gallium-arsenide low-barrier diodes with near-surface δ-doping

The results of experimental studies of the effect of rapid thermal annealing on low-barrier diode structures used in the fabrication of microwave detectors for imaging arrays are indicative of an increase in the effective barrier height. Assuming that this effect is related to the diffusion spreading of the silicon δ-doped layer, which determines charge transport in the modified diode, a theoretical model is developed and the diffusion coefficient for silicon in the near-surface region of gallium arsenide (D ≈ 2 × 10^?14 cm²/s at 600°C) is estimated. A comparison with published data makes it possible to assume that diffusion in the near-surface layers is greatly facilitated compared to that in the bulk. It is suggested that the cause of acceleration of the diffusion can be a high electric field formed by the charged plane of the detector and it can also be related to an increased density of defects near the surface. The practical result consists in the emerging possibility of increasing (within a certain range) the effective barrier height in the grown structures, which will make it possible to adapt the parameters of low-barrier diodes to the optimal value in order to obtain sensitive detectors.     

Structure and optical properties of heterostructures based on MOCVD (Al x Ga1 − x As1 − y P y )1 − z Si z alloys

Epitaxial heterostructures produced by MOCVD on the basis of Al _x Ga_{1 ? x} As ternary alloys with the composition parameter x ≈ 0.20–0.50 and doped to a high Si and P atomic content are studied. Using the high-resolution X-ray diffraction technique, scanning electron microscopy, X-ray microanalysis, Raman spectroscopy, and photoluminescence spectroscopy, it is shown that the epitaxial films grown by MOCVD are formed of five-component (Al _x Ga_{1 ? x} As_{1 ? y} P _y )_{1 ? z} Si _z alloys.     

A study of galvanomagnetic phenomena in MBE-grown n-CdxHg1−x Te films

The magnetic-field dependences of the Hall coefficient and the conductivity of n-type Cd_xHg_1?x Te epitaxial structures were measured at 77 K. The structures were grown by molecular-beam epitaxy with a prescribed solid solution composition profile across the thickness. A specific feature of the obtained dependences is that the conductivity and the absolute value of the Hall coefficient decrease with an increasing magnetic field. The obtained experimental dependences can only be described in terms of a model including low-mobility electrons. It is shown that anodic oxide deposited onto the Cd_xHg_1?x Te film surface makes the concentration of low-mobility electrons higher and that of anodic fluoride lower. The possible reasons for the appearance of low-mobility electrons are discussed. The most probable sources of such electrons are surface layers and electrical microheterogeneities in Cd_xHg_1?x Te films.     

Microdeformations of the crystal lattice of PbTe1 − x Br x solid solutions

Microdeformations of the crystal lattice of PbTe_{1 ? x} Br _x solid solutions depending on the bromine content are determined by analysis of the physical broadening of X-ray reflections. It is found that they increase with the introduction of bromine from 0.188% (for undoped PbTe) to 0.283% for PbTe_{1 ? x} Br _x at x = 0.02. The microstrains remain constant with a further increase in the bromine content.