TeCd antistructural defects in CdTe crystals

Two-temperature annealing with a controlled vapor pressure of tellurium P _Te2 is used to study CdTe〈Cl〉 crystals under conditions of high-temperature thermodynamic equilibrium of the crystal with the gas phase (735–940 °C). For low pressures P _Te2 (≥P _min) Cl_Te+ begins to condense because of the formation of V_Cd ⁻² in the crystal. As P _Te2 increases, this mechanism of exact self-compensation no longer operates because of the formation of Te_Cd+ intrinsic antistructural point defects. Pis’ma Zh. Tekh. Fiz. 23, 30–34 (February 26, 1997)     

High pressure and high temperature annealing on nitrogen aggregation in lab-grown diamonds

Diamond single crystals were grown by a high-pressure high-temperature gradient method using a molten Fe–Ni catalyst in a split-sphere apparatus at a pressure of 5.5 GPa and a temperature of 1473–1873 K. The as-grown crystals, ranging in size from 0.2 to 0.6 g, were generally deep yellow in color because of intake of nitrogen impurity during the process. Two different annealing methods were used to change their color to light and vivid yellow. One method involved annealing at 5.5 GPa and 2193–2473 K within the split-sphere apparatus. The other involved annealing of E-beam irradiated crystals at 1773 K in a high-vacuum furnace at 10⁻⁶ Torr. Distribution of C-center nitrogen, single substitutional nitrogen, and A-center nitrogen defects, a pair of nearest-neighbor nitrogen, were thoroughly studied by FT–IR spectroscopy. Upon annealing, C-center nitrogen defects decreased by 10–60%, while A-center nitrogen defects increased by 5–70%. It was confirmed that the irradiation process and intake of nickel impurity enhanced the nitrogen aggregation rate, which followed the second order kinetics. Measured activation energies were in the range of 2.88–3.01 eV, which were not strongly affected by the irradiation process. The results indicate that the nitrogen aggregation rate was enhanced by vacancies and interstitials introduced by E-beam irradiation.     

Effect of annealing on the spectroscopy performance of YVO4:Ce3+ single crystals

In this study, 1.0 at.% YVO₄:Ce³⁺ single crystals were grown in the protective atmosphere by using the Czochralski method. The crystals were annealed in Ar and H₂ atmospheres at different temperatures. The absorption and fluorescence spectra of the samples before and after annealing were measured. Results showed that the luminescent efficiency of the crystals was significantly enhanced after annealing in H₂ than after annealing in Ar. This phenomenon can be attributed to the existence of some Ce⁴⁺ ions in the crystal lattice. These Ce⁴⁺ ions can be effectively reduced to Ce³⁺ via annealing in H₂. With a fixed annealing time in H₂, the luminescent intensity significantly increased with increasing annealing temperature. The possibility of the crystal as white light material was also discussed according to the luminescence properties.     

Ion-beam-induced modification of the electrical properties of vacancy-doped mercury cadmium telluride

The effect of ion-beam milling (IBM) on the electrical properties of vacancy-doped mercury cadmium telluride (MCT) p-Hg_1−x Cd _x Te (x ∼ 0.22) has been studied. The samples were prepared by thermal annealing of molecular beam epitaxy (MBE)-grown heterostructures and the films and single crystals grown by liquid-phase epitaxy (LPE). The etching of samples by IBM resulted in the formation of donor centers. In MBE-grown heterostructures (but not in LPE-grown samples), the concentration of these centers reached ∼10¹⁷ cm⁻³. It is established that the appearance of a high concentration of donor centers in the heterostructures is caused by the IBM-induced activation of neutral defects formed during epitaxial growth. The probable nature of defects is discussed.     

溶剂熔区移动法生长Cd0.9Zn0.1Te晶体的工艺优化研

为了解决Cd_0.9Zn_0.1Te(CZT)晶体生长温度高、单晶率低、成分不均匀等问题, 采用溶剂熔区移动法(THM)在优化工艺参数下生长了掺In的CZT晶体, 在优化晶体的生长温度、固液界面处的温度梯度、原位退火过程等生长条件后, 生长出直径为45 mm的低Te夹杂浓度、高电阻率、高透过率、均匀的高质量CZT晶体。 X射线衍射结果显示, 晶体的结晶性较好、Zn成分轴向偏析小。红外透过光谱测试结果显示, 晶体内部的杂质、缺陷水平相对较少, 晶体整体的红外透过率在60%左右。紫外-可见光吸收光谱测试结果也进一步表明, 晶体的均匀性良好。采用红外显微镜对晶体内部的Te夹杂形貌及其尺寸进行观察, 结果表明Te夹杂的尺寸主要分布在0~10 μm之间。采用直流稳态光电导技术测得电子的迁移率寿命积约为8×10^-4 cm²/V。     

Effects of gradient heat treatment on Te-rich CdZnTe crystal

The gradient heat treatment was performed on Te-rich CZT crystal grown by the vertical Bridgman (VB) method, which was under the temperature of 1073 K and the temperature gradient of 2 K/mm and the velocity of 1.8 mm/h. IR transmission, IR microscope, I-V curves and glow discharge mass spectrometry (GDMS) revealed that Te inclusions moved towards the last-to-freeze region in CZT ingot, which proved that the gradient heat treatment has the possibility to purify the CZT ingot. Finally, after the gradient heat treatment, the resistivity of the CZT ingot was enhanced, and the IR transmittance was also improved.     

Charge transport properties of as-grown CZT by traveling heater method

In this present work we have grown Cd_0.9Zn_0.1Te doped with indium by the traveling heater method (THM) technique. Large 2 in diameter CZT ingots of more than 1 kg each were successfully grown by the THM technique in vertical configuration. In order to evaluate our as-grown CZT samples, charge transport characteristics were studied at and below room temperature. The key parameter investigated for as-grown CZT samples was the mobility-trapping time product and its temperature variation. Mobility-trapping time values as high as 9×10⁻³ cm²/V at 30 °C were measured for samples exhibiting resistivities in the 1-2×10¹⁰ Ω cm range. The as-grown samples showed moderately good resolution of 1.5-3.5% at 662 keV when fabricated. The variation of the internal electric field along the depth of the detector was studied for as-grown material to evaluate deformations inside the crystal due to the presence of residual stress or other defects.     

Use of near-infrared as a screening technique for CdZnTe substrates

Epitaxial layers of Cd _x Hg_1–xTe (CMT) are grown onto Cd_1–yZn _y Te (CZT) substrates in order to minimize misfit dislocations at the growth interface. For long wavelength focal plane array infrared detector requirements x = 0.22 CMT is nominally lattice matched to CZT alloys with y ~ 0.04. However, the rate of change of lattice parameter, as a function of y, means that the uniformity and definition of the required Zn concentration is important. We report here a non-contact, non-destructive technique for screening/mapping CZT substrates using the near infrared (NIR) band edge cut-on, defined by the wavelength corresponding to an absorption coefficient () = 10cm^–1, which automatically corrects for thickness or transmission variations. Details of the experimental set-up and a novel holder for vertical mounting of substrates are given. A comparison of results from this technique and X-ray diffraction (XRD) lattice parameter data is also presented.     

Deposition of AgGaS<Subscript>2</Subscript> thin films by double source thermal evaporation technique

In this study, polycrystalline AgGaS₂ thin films were deposited by the sequential evaporation of AgGaS₂ and Ag sources with thermal evaporation technique. Thermal treatment in nitrogen atmosphere for 5 min up to 700 °C was applied to the deposited thin films and that resulted in the mono phase AgGaS₂ thin films without the participation of any other minor phase. Structural and compositional analyses showed the structure of the films completely changes with annealing process. The measurements of transmittance and reflectance allowed us to calculate the band gap of films lying in 2.65 and 2.79 eV depending on annealing temperature. The changes in the structure with annealing process also modify the electrical properties of the films. The resistivity of the samples varied in between 2 × 10³ and 9 × 10⁶ (Ω-cm). The room temperature mobility depending on the increasing annealing temperature was in the range of 6.7–37 (cm² V⁻¹ s⁻¹) with the changes in carrier concentrations lying in 5.7 × 10¹³–2.5 × 10¹⁰ cm⁻³. Mobility-temperature dependence was also analyzed to determine the scattering mechanisms in the studied temperature range with annealing. The variations in the electrical parameters of the films were discussed in terms of their structural changes.     

Characterisation of vacancy-like defects in III–V compound semiconductors using positron annihilation technique

Single crystals of GaP and InSb were irradiated by 3 MeV electrons at 20 K to a total dose of 4 × 10¹⁸ e ⁻/cm². Isochronal annealing in the temperature region 77–650 K followed the irradiation. In GaP, the positron lifetime measurement indicated the presence of irradiation-induced vacancies in the Ga-sublattice. The vacancies disappeared at two stages observed in temperature ranges 200–300 and 450–550 K. In InSb the positron lifetime was found to increase by 8 ps compared to that in as-grown crystals (i.e. 282±2 ps) after irradiation. The increase indicated the presence of irradiation-induced defects; the crystal was found to recover until 350 K with a sharp annealing stage at 250–350 K.     

Sol–gel derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films: effect of annealing on structural,morphological and optoelectronic properties

Nanocrystalline Co₃O₄ thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co₃O₄ thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co₃O₄ films is improved by annealing. The dc electrical conductivity of Co₃O₄ thin films were increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 10¹⁹ cm⁻³ and 5.2–7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹ respectively. It is observed that Co₃O₄ thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Thermal stability and annealing behavior of photoluminescence from Eu doped YAG

Eu₂O₃ doped Y₃Al₅O₁₂ (YAG) crystals have been grown using a floating zone technique and evaluated thermal stability and annealing behavior of PL for a fluorescence thermo-sensor application. Color of the crystals grown varies from deep purple to colorless with O₂ concentration of the growth atmosphere and annealing in air. Photoluminescence (PL) peaking at λ = 590, 607, 624, 647 and 709 nm due to Eu³⁺ ions are observed from the crystals under UV excitation. Anomalous temperature dependence of PL intensity, which is observed in as-grown crystals, is improved greatly by annealing through the heat cycle. From annealing behavior of optical absorption spectra, residual Eu²⁺ ions are suggested to be responsible for the de-coloration and the improvement of anomalous temperature dependence of Eu doped YAG crystals.     

Electrical and optical properties of P-doped ZnO thin films by annealing temperatures in Nitrogen ambient

The effects of post-annealing temperature on the optical and electrical properties of P-doped ZnO thin films, grown on sapphire substrate, have been investigated when the annealing is performed under nitrogen ambient. Analysis of the XRD shows that regardless of the post-annealing temperature, the P-doped ZnO thin films have grown the (002) peak. The full width of half maximum decreases from 0.194 to 0.181° as the annealing temperature increases from 700 to 900 °C. This phenomenon means that the increase of annealing temperature causes enhancement of the thin film’s crystalline properties. The results of Hall effect measurements indicate that the P-doped ZnO thin films, annealed at 750 and 800 °C exhibit p-type behavior, with hole concentrations of 5.71 × 10¹⁷ cm⁻³ and 1.20 × 10¹⁸ cm⁻³, and hole mobilities of 0.12 cm²/Vs and 0.08 cm²/Vs, respectively. The low-temperature (10 K) photoluminescence results reveal that the peaks related to the neutral-acceptor exciton (A⁰X) at 3.355 eV, free electrons to neutral acceptor (FA) at 3.305 eV and donor acceptor pair (DAP) at 3.260 and 3.170 eV are observed in the films showing p-type behavior with the acceptors. Because P atoms replace O atoms to produce acceptors from P-doped ZnO thin films by the thermal activation process at the appropriate annealing temperature with nitrogen ambient, the p-type ZnO thin films can be fabricated in this way.     

Optically rewritable Bragg gratings in Mn2+ doped RbCdF3

Optical absorption, optically stimulated luminescence, and thermo-luminescence measurements have been made on RbCdF₃:Mn²⁺ single crystals with the aim of characterizing this compound for holographic storage. We show that there are stable traps that are filled after deep ultra-violet irradiation (<270 nm) and they can be emptied after ∼365 nm irradiation. The photo-induced changes in the optical properties can be used to create optically rewritable Bragg gratings in these crystals.     

Thermally stable and low-resistance W/Ti/Au contacts to n-type GaN

We report on the formation of thermally stable and low-resistance Ti/Au-based ohmic contacts to n-type GaN (4.0 × 10¹⁸ cm⁻³) by using a W barrier layer. It is shown that the electrical characteristic of the sample is considerably improved upon annealing at 900 °C for 1 min in a N₂ ambient. The contacts produce the specific contact resistance as low as 6.7 × 10⁻⁶ Ω cm² after annealing. The Norde and current–voltage methods are used to determine the effective Schottky barrier heights (SBHs). It is shown that annealing results in a reduction in the SBHs as compared to that of the as-deposited sample. Auger electron spectroscopy (AES), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) examinations show that nitride and gallide phases are formed at the contact/GaN interface. Based on the AES, STEM and XRD results, a possible ohmic formation mechanism is described and discussed.     

One-step and iterative thermo-mechanical treatments to enhance Σ3n boundaries in a Ti-modified austenitic stainless steel

The article discusses the results of a study on low-strain thermo-mechanical (one-step and iterative) processing to enhance Σ3 ⁿ boundaries in a Ti-modified austenitic stainless steel (alloy D9). Solution annealed (SA) specimens were subjected to 10% thickness reduction by rolling followed by annealing at 1173, 1223, and 1273 K for 0.5, 1, and 2 h. Anomalous grain growth with moderate increase in Σ3 ⁿ boundaries was observed after annealing at 1,173 K for 0.5 to 2 h. Prolific multiple twinning with minimum deviation of Σ3 and Σ9 boundaries from ideal orientation was achieved after annealing at 1,273 K for 0.5 to 2 h. A significant disruption in random boundary connectivity was obtained in these conditions due to the presence of large number of Σ3-Σ3-Σ9/Σ3-Σ9-Σ27 triple junctions. Iterative processing (up to 4 cycles) employing 10% thickness reduction followed by annealing at 1,273 K for 0.5 h revealed fluctuations in the evolution of Σ3 boundaries. The Σ3 fraction increased after 2nd and 4th iteration and there is a drop after 3rd iteration. This was attributed to the increased driving force for grain boundary migration due to dislocation pile-up at twin boundaries during earlier iterations. A two step iterative processing comprising of 10% deformation followed by annealing at 1,273 K for 0.5 h is the recommended thermo-mechanical processing to achieve enhanced fraction of Σ3 ⁿ boundaries (~73%) in alloy D9.     

Study of polycrystalline ZnTe (ZnTe:Cu) thin films for photovoltaic cells

In our work, polycrystalline ZnTe and ZnTe:Cu thin films were deposited by vacuum co-evaporation technology. The conductivity–temperature relationship was measured. And the properties of films were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and differential scanning calorimety (DSC). The results show that the as-deposited films are cubic and that the films annealed at 185°C are cubic and hexagonal. Cu _x Te are observed by XRD and XPS. DSC shows ZnTe:Cu film has a peak of decalescence at 170°C, which means that there can be a change. Therefore we assume ZnTe:Cu thin films have structure changes at 185°C and the existence of Cu _x Te leads to the abnormal conductivity–temperature relationship. During annealing, copper diffuse from grain boundary to lattices. 1/C ²-V curves show that Cu _x Te can form tunneling junction with CdTe, which can improve the back contact.     

Crystallization of (Fe,Mn)-based nanoparticles in sodium-silicate glasses

In this investigation, glasses from the system Na₂O/MnO/SiO₂/Fe₂O₃ are prepared using a conventional glass-melting technique. During annealing the glass, a nanocrystalline (Fe, Mn)-based spinel phase is precipitated. The phase composition and microstructure of the formed glass–ceramics are studied using X-ray diffraction and electron microscopy. Anomalous small-angle X-ray scattering experiment is used to gather information on the size, composition and element distribution for the precipitated (Fe, Mn)-based nanocrystals. The sizes of the formed spinel crystals, as determined by scanning electron microscopy and anomalous X-ray scattering, are in the range from 12 to 50 nm for annealing temperatures in the range from 550 to 700 °C. Annealing for a longer period of time at temperatures ≥600 °C results in the formation of a second crystalline phase, NaFe(SiO₃)₂ (aegirine). The ASAXS data show the formation of core–shell structure for the (Fe, Mn)-based crystals with core consisting mostly of iron oxide and a shell, depleted of Fe and Mn. The growth of the spinel crystals is assumed to be kinetically self-constrained.     

Charge Disproportionation and Superconductivity in Tl- and In-doped Lead Telluride

The “negative-U model” is analyzed and applied to Tl- and In-doped lead telluride, Pb_1−x Tl _x Te, and Pb_1−x In _x Te, respectively. The former, but not the latter, is superconducting (T _c<1.5 K) in a certain concentration range (x _c>0.003). At very low concentrations, carriers are created in the valence band and the conductivity is metallic, of the ordinary kind. Matsushita et al. and Erickson et al. explain this as due to disproportionation 2Tl²⁺→Tl⁺ and Tl³⁺. The latter authors are of the opinion that indium also disproportionates in the same way as thallium. If this would be the case, it would be hard to explain the absence of superconductivity at indium doping. In this paper it is shown that In²⁺ does not disproportionate under the given circumstances. The Hubbard model, extended and generalized, is therefore consistent with all experimental results.     

Distribution of Au atom number in the Au agglomerates generated during the out-diffusion process of supersaturated high-temperature substitutional Au in Si at 900 °C

Au atom number in the Au agglomerates generated during the annealing of supersaturated high-temperature substitutional Au in Si at 900 °C are measured by SIMS and their distributions have been investigated. The annealing time is chosen as 22.5, 90 or 360 h, which corresponds to initial, middle or near final stage of the annealing. Many “initial agglomerates” containing about 2.0 × 10⁵ Au atoms are generated and the distributions show an abrupt one with the peak at the atom number in the initial and middle stages. The “initial agglomerates” have absorbed supersaturated Au atoms within 0.86 μm. The “initial agglomerates” are generated even in the near final stage and grow up to containing about 4 × 10⁶ Au atoms by absorbing the Au atoms within 2.3 μm, finally. As the consequence, many agglomerates contain 5 × 10⁴–1.3 × 10⁶ Au atoms resulting in a broad distribution at the near final stage. Schematic models of agglomerations corresponding to each stage are proposed.