Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Influence of plastic deformation on the photoconductivity of CdTe

Investigation of photoconductivity have been performed on p-type phosphorus doped CdTe (5 × 10¹⁵ cm⁻³) deformed by compression at room temperature. Using a technique of axial illumination, the contribution of the surface to the photoconductivity is suppressed. In the investigated energy range (0.08–1.54 eV), and at room temperature, a maximum of the signal of the non-deformed material is of found at 1.312 ± 0.009 eV, with a half width of 0.100 eV, whereas the 0.3% deformed material presents a maximum at 1.348 ± 0.009 eV with the same half width. At 223 K these peaks are shifted to higher energies, the half width remaining unchanged, and the amplitudes being ∼ 30 times higher.     

Non-stoichiometry of apatites at high temperatures

Schottky defects in apatites are formed by a decomposition reaction at temperatures in excess of 1000°K. In this investigation thermogravimetrie experiments on fluorapatite single crystals and powders have been carried out in the temperature range 1000–1600°K. Relative weightlosses of 1.2 × 10⁻³ per hour corresponding to Ca/P decreases of 0.0002 per hour have been observed at 1675°K. In the temperature range studied the number of vacancy triplets formed per second is in the order of 10¹⁸. The activation energy (1.15 eV) involved indicates that dislocations might play an important role in the decomposition process.     

Crystal Data,Electrical Resisitivity and Mobility in Cu3In5Se9 and Cu3In5Te9 Single Crystals

X-ray powder diffraction data were obtained for Cu₃In₅Se₉ and Cu₃Te₉, which were found to crystallize in orthorhombic and tetragonal systems, respectively. The electrical resistivities and Hall mobilities of these compounds were investigated in the temperature range 35–475 K. Cu₃In₅Se₉, was identified to be n-type with a room temperature resistivity of 3 × 10³ Ω·cm which decreases with increasing temperature. For T < 65 K impurity activation energy of 0.03 eV and for T > 350 K onset of intrinsic conduction yielding a band gap energy of 0.99eV were detected. The neutral impurity scattering was found to dominate at low temperatures, while in the high temperature region thermally activated mobility was observed. Cu₃In₅Te₉ exhibits p-type conduction with a room temperature resistivity of 8.5 × 10⁻³ Ω·cm decreasing sharply above 400 K and yielding an impurity ionization energy of 0.13 eV. The temperature dependence of mobility indicates the presence of lattice and ionized impuritiy scattering mechanisms above and below 160 K, respectively.     

Untersuchung epitaktischer Molybdänkarbidschichten an Molybdän-(110)-Oberflächen

The initial phases of high temperature (1700 K) carburization of (110) molybdenum surfaces by C₆H₆ at low pressure are examined with low energy electron diffraction (LEED) and emission electron microscopy. After an exposition of about 8 · 10⁻⁵ Torr · sec a (4 × 4) superstructure was observed by means of LEED, interpreted as coincidence lattices with the Mo₂C (10.0) plane parallel to the Mo (110) surface. Heating a sample without further exposition resulted in the appearance of a complex and of a (2 × 2) superstructures. After an exposition of about 2 … 9 · 10⁻³ Torr · sec needle shaped molybdenum carbide crystallites grew on the surface into the [111] and [111] directions. The orientation Mo₂C (10.1) parallel to Mo (110) was concluded from the LEED patterns.     

Determination of optical parameters of Ga0.75In0.25Se layered crystals

The optical properties of the Ga_0.75In_0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380–1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10–300 K. The rate of change of band gap energy (γ = –6.2 × 10^–4 eV/K) and absolute zero value of the band gap (E_gi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index values. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical Characterization of Irradiation plus Annealing – induced VAsZnGa Pairs in p-type GaAs (Zn) Crystals

Effect of fast electron irradiation (E =2.2 Mev, ϕ_c = 1 × 10¹⁶ el/cm²) and subsequent annealings (T = 150 to 350 °C, t = 10 to 600 min) of zinc-doped p-type GaAs crystals on the formation and dissociation of V_AsZn_Ga, pairs is studied. An analysis of the formation and dissociation kinetics of V_AsZn_Ga pairs permitted to find the diffusion coefficient of radiation-induced arsenic vacancies D(D = 1.5 × 10⁻¹⁸, 1 × 10⁻¹⁷ and 5 × 10⁻¹⁷ cm²/s at 150, 175 and 200 °C accordingly), their migration energy ϵ_m(ϵ_m = 1.1 eV), the binding energy of V_AsZn_Ga, pairs ϵ_b(ϵ_b = 0.5 eV), and also their dissociation energy ϵ_d(ϵ_d = 1.6 eV).     

Temperature dependence of electrical conductivity and hall effect of Ga2Se3 single crystal

Electrical conductivity (σ) and Hall coefficient (R_H) of single crystal grown from the melt have been investigated over the temperature range from 398 K to 673 K. Our investigation showed that our samples are p-type conducting. The dependence of Hall mobility an charge carrier concentration on temperature were presented graphically. The forbidden energy gap was calculated and found to be 1.79 eV. The ionization energy of impurity level equals 0.32 eV approximately. At 398 K the mobility equals to 8670 cm² V⁻¹ s⁻¹ and could described by the law μ = aTⁿ (n = 1.6) in the low temperature range. In the high temperature range, adopting the law μ = bT^–m (as m = 1.67), the mobility decreases. This result indicates that in the low temperature range the dominant effect is scattering by ionized impurity atoms, whereas in the high temperature range the major role is played by electron scattering on lattice vibrations (phonons). At 398 K the concentration of free carriers showed a value of about 1.98 × 10⁷ cm⁻³.     

An AES/XPS study of oxygen involved reactions on InSb

The oxidation of ion-etched InSb(110)-cleavage planes was investigated by means of AES and XPS, respectively. Whereas the sticking coefficient of oxygen at indium sites was found to reach a saturation value after slight ion bombardment, the oxygen uptake rate of antimony remains low (sticking probability in the 10⁻⁷ range) with raising ion dose to a point where a drastical change in oxidation behaviour occurs at ion doses in the 10⁻² As · cm⁻² range. Then indium and antimony are nearly simultaneously oxidized with sticking coefficients of roughly 10⁻³. Cluster formation is discussed as one possible mechanism to explain the experimental findings. Adsorption experiments on disordered surfaces can contribute to a better understanding of surface reactions during gas phase growth of single crystals, since the in-growth situation of the top layer of the latter is far away from the ideal situation that is prepared by in situ cleaving only.     

AES Depth Profiling of Nitrogen Implanted Fe(001)

Auger electron spectroscopy (AES) combined with a well controlled ion mill is applied for the study of nitrogen implanted (N⁺₂ ions, 120 keV) into iron single crystals in doses ranging from 8 × 10¹⁶ to 5 × 10¹⁷ N-atoms/cm², also with subsequent heat treatment. The nitrogen depth profiles are Gaussian-like in shape for doses up to 1.5 × 10¹⁷ N-atoms/cm². Athigher doses deviations are observed. The nitride bonding state was indicated but a part of the implanted nitrogen appears to be weakly bonded.     

Auger spectrometric studies on fracture surfaces of tool steel

The fracture surfaces of tool steel K-13 (Hungarian Standard) were studied by Auger electron spectroscopy. Notched specimens of 3 × 3 mm² were fractured in UHV (6 × 10⁻⁸ Pa) with a fracturer (Riber FR 100) and studied with a CMA analyser (Riber OPC 103). With our modification the fracturer was operated within the −150°C −+230°C temperature range. The fracture surfaces were tested with a scanning electron microscope (JEOL JSM 35). The evaluation of Auger spectra was based on the PHI (PALMBERG et al.). Handbook, however the backscattering correction of Jablonski was applied in some cases. The choice of adequate fracturing temperature proved to be very important. Low temperature fracture of this steel alloy is producing very rigid transgranular fracture. The effects of sample heat treatment and of fracturing temperature as well were studied in details. The Auger spectra of fracture surfaces are strongly affected by the heat treatment of the samples. The grain boundary fracture surface of a sample austenitized at 1100°C quenched and tempered at 600°C exhibited a strong enrichment of P, correlating with the enrichment of Cr, V and Mo. The transgranular fracture surface of the same sample but without tempering corresponded to the bulk composition. In some cases and spots on the fracture surfaces, giant S or P peaks were associated with secondary phases (inclusions) on the SEM pictures.     

Influence of thermal annealing on the composition and structural parameters of DC magnetron sputtered titanium dioxide thin films

Titanium dioxide films have been deposited using DC magnetron sputtering technique. Films were deposited onto RCA cleaned p‐silicon substrates at the ambient temperature at an oxygen partial pressure of 7 × 10^–5 mbar and sputtering pressure of 1 × 10 ^–3 mbar. The deposited films were annealed in the temperature range 673–873 K. The structure and composition of the films were confirmed using X‐ray diffraction and Auger electron spectroscopy. The structure of the films deposited at the ambient was found to be amorphous and the films annealed at 673 K and above were crystalline with anatase structure. The lattice constants, grain size, microstrain and the dislocation density of the film are calculated and correlated with annealing temperature.     

Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1‐x) mixed crystals (0.25 ≤ x ≤ 1)

The optical properties of the TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400–1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS_2xSe_2(1‐x)mixed crystals. The transmission measurements carried out in the temperature range of 10–300 K revealed that the rates of change of the indirect band gaps with temperature are γ = –9.2×10^–4 eV/K, –6.1×10^–4 eV/K, –4.7×10^–4 eV/K and –5.6×10^–4 eV/K for TlInS₂, TlInS_1.5Se_0.5, TlInSSe and TlInS_0.5Se_1.5 crystals, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Incorporation of nitrogen into galliumarsenide grown by chloride VPE

The incorporation of nitrogen into GaAs in the halide-VPE system using NH₃ as the doping source is investigated. The concentration of incorporated N depends on the NH₃ flow rate and increases with decreasing deposition temperature. Concentrations up to 6 × 10¹⁷ cm⁻³ could be detected far above the calculated equilibrium value. By a comparison of SIMS-data with those obtained from IR it is found that most of the N-atoms are situated substitutionally on As lattice sites. Normal-pressure 2 K photoluminescence measurements show N-related luminescence peaks at 1.508 and 1.496 eV. Most probably this luminescence arises from complexes of N with undeliberately introduced impurities. For the 1.508 eV center a complex Si_Ga-N_As is discussed. — A new N-related metastable deep center with the energy levels E_c-0.33, E_c-0.41, and E_c-0.68 eV could be found by DLTS.     

Deep levels and growth conditions of LPE GaAs crystals

Deep levels in LPE GaAs were studied in relation to growth conditions. The residual deep levels in LPE layers are hole traps 0.50 and 0.65 eV above the top of the valence band. Their concentrations are of the order of 10¹³ cm^-3 for growth temperatures between 650 and 840°C, and increase with increasing growth temperature. The activation energy of incorporation is about 0.7 eV, which is very close to that of an arsenic vacancy. It is also noted that their concentrations near the grown surface are independent of the growth temperature. This indicates that the hole traps undergo an annealing effect after the growth period. From the experimental results for Fe and oxygen doping, each impurity acts as a deep level only when it makes a complex defect with a gallium vacancy, otherwise they are shallow levels, The distribution coefficients at 750°C are 1 × 10^-7 and 1.1 × 10^-5 for the deep and Fe and the shallow acceptor, respectively.     

Electrical conductivity and thermoelectric power of liquid AgSb Te2

The electrical conductivity and thermoelectric power of liquid AgSb Te₂ have been investigated as a function of temperature. Experimental data are analyzed in terms of a recent model proposed by Mott. The activation energy for electrical conductivity and thermoelectric power is found to be approximately 0.50 eV with a large temperature coefficient γ ～ 7 × 10^?4 eV/deg K. The gradual transition from a semiconducting to a metallic behaviour has been observed at high temperature.     

Fluorine laser-induced silicon hydride Si–H groups in silica

Formation and destruction of silicon hydride (Si–H) groups in silica by F₂ laser irradiation and their vacuum ultraviolet (VUV) optical absorption was examined by infrared (IR) and VUV spectroscopy. Photoinduced creation of Si–H groups in H₂-impregnated oxygen deficient silica is accompanied by a growth of infrared absorption band at 2250 cm⁻¹ and by a strong increase of VUV transmission at 7.9 eV. Photolysis of Si–H groups by 7.9 eV photons in this glass was not detected when the irradiation was performed at temperature 80 K. However, a slight destruction of Si–H groups under 7.9 eV irradiation was observed at the room temperature. This finding gives a tentative estimate of VUV absorption cross section of Si–H groups at 7.9 eV as 4 × 10⁻²¹ cm², showing that Si–H groups do not strongly contribute to the absorption at the VUV fundamental absorption edge of silica glass.     

Growth,electrical and optical behaviour of nanocrystalline Ag2Cu2O3 films produced by RF magnetron sputtering

Thin films of Ag₂Cu₂O₃ were formed on glass substrates by RF magnetron sputtering technique under different oxygen partial pressures in the range 5 × 10^‐3 – 8 × 10^‐2 Pa using mosaic target of Ag₇₀Cu₃₀. The influence of oxygen partial pressure on the core level binding energies, crystallographic structure, and electrical and optical properties of the deposited films was studied. The atomic ratio of copper to silver in the films was 0.302. The oxygen content was in correlation with the oxygen partial pressure maintained during the growth of the films. The films formed at oxygen partial pressures < 2 × 10^‐2 Pa was mixed phase of Ag₂Cu₂O₃ and Ag. The films deposited at 2 × 10^‐2 Pa were single phase of Ag₂Cu₂O₃. The crystallite size of the films formed at 2 × 10^‐2 Pa was 12 nm, while those films annealed at 473 K was 16 nm. The nanocrystalline Ag₂Cu₂O₃ films formed at oxygen partial pressure of 2 × 10^‐2 Pa showed electrical resistivity of 8.2 Ωcm and optical band gap of 1.95 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Comparison of lead solubility in NaCl crystals from data obtained by different methods

The solvus of the NaCl: Pb²⁺ system was found in the concentration range from 1.5 × 10⁻³ to 1.9 × 10⁻² mol% at temperatures ranging from 375 to 430 °C from the data of flotation measurements of the crystal density. The heat of impurity dissolution equal to 2.0 ± ± 0.6 eV and the change in the vibrational entropy in the formation of the solid solution S_v/K= 20 ± 10 were determined. Reasons for a difference in the estimates of lead solubility in NaCl, obtained from temperature dependences of light scattering and by other methods: measurement of the density, electric conductivity, and the electron-microscopic decoration of the same crystals are discussed.