Effect of temperature on thermally induced defects in silicon

Deep level transient spectroscopy has been used to study thermally activated defects in silicon. It has been observed that different annealing temperatures activate different defects in silicon, which were lying on inactive sites before annealing. Two deep mid-gap levels at energy positions E _c −0.48 eV and E _c −0.55 eV were found to be introduced by different heat treatments. It is also noted that heat treatment at 1,250 °C suppresses the concentration of deep level at E _c −0.23 eV and enhances the concentration of deep level at E _c −0.25 eV, while heat treatment at 950 °C has an opposite effect. Annealing response of the level at E _c −0.48 eV is found different to the annealing response of the level at E _c −0.55 eV which suggests them two different levels.     

Structure and electrical conductivity of selenium-ion-implanted CdSe films

We have studied the effect of annealing on the spectral and photoelectric properties of polycrystalline CdSe films produced by thermal evaporation and implanted with Se ions to doses from 5 × 10¹⁵ to 5 × 10¹⁶ cm⁻². The results demonstrate that, when cadmium vacancies and selenium interstitials are major defects, annealing leads to the formation of microcrystalline two-phase layers during recrystallization, which have low p-type conductivity due to a shallow acceptor at E _v + 0.04–0.05 eV, related to interstitial selenium.     

Annealing behavior of light-induced metastable defects in a-Si1−x C x : H

We have used the room-temperature constant-photocurrent method and dark-conductivity measurements to study the annealing kinetics of light-induced metastable defects in a set of a-Si_1?x C _x : H (x≤0.11) films. Light-induced metastable defects created at room temperature started annealing at higher temperatures for alloys with high carbon contents. The annealing activation-energy distribution function was calculated to be a narrow Gaussian peaked at about 1 eV for the unalloyed sample. For the alloys, the peak position shifts to higher energies with increasing carbon content. The variation of the dark conductivity of the samples was measured as a function of annealing time and annealing temperature. A similarity between the observed increase in the dark conductivity and the annealing rate of light-induced defects was identified.     

Iron and gold related defects in water quenched silicon

Thermally induced defects in heat-treated and then quenched in water n-silicon samples have been studied using deep level transient spectroscopy. Two deep levels at energies E _c – 0.48 eV and E _c – 0.25 eV are observed in high concentration. The emission rate signatures and annealing characteristics showed the DLTS signal due to level at energy position E _c – 0.48 eV is not only due to Au(A) but some other level also contributes to this signal. The energy state at E _c – 0.25 eV is identified to be pinned with E _c – 0.48 eV. The annealing characteristics also revealed the contribution of Au–Fe complex in DLTS signal of E _c – 0.25 eV level. A complementary behavior of these two levels in annealing characteristics has also been observed.     

Relaxation processes with conductivity as-physical parameter in amorphous GeXSe1−X films

Relaxation processes in amorphous Se_XGe_1−X films are studied with electrical conductivity as a physical parameter. After a review of the essential theories, experimental results for x = 0.08, 0.12 and 0.16 are presented either at room temperature or with annealing. The relaxation processes are found to be governed by a distribution of activation energies and the corresponding activation energy spectrum is proposed for x = 0.08 and x = 0.12 with a maximum value at 0.87 and 0.92 eV respectively. This enables us to interpret the phenomenon in terms of defects elimination: C₃ being eliminated with the apparition of the so called VAP (C₃⁺, C₁⁻) which are in turn progressively eliminated with weaker energies.     

Interaction of copper atoms with radiation-induced defects in silicon

The annealing behavior of radiation-induced defects in Czochralski-grown n-type Si crystals doped with copper via high-temperature (600 and 650°) indiffusion has been studied using Hall effect measurements and deep level transient spectroscopy. The results indicate that radiation-induced vacancy-type defects (divacancies V ₂ and vacancy-oxygen complexes VO) are effective traps for copper atoms. The inter- action of Cu with VO and V ₂ reduces their annealing temperature and leads to the formation of electrically active centers at E _c − 0.60 eV and E _c − 0.17 eV, which are assumed to be Cu-VO and Cu-V ₂ complexes. The enhanced annealing of the radiation-induced vacancy-type defects in Si〈Cu〉 is due to the fact that these defects capture Cu interstitials released from neutral Cu-containing associates at temperatures above 150°C.     

Annealing effect of thermal spike in MgO thin film prepared by cathodic vacuum arc deposition

MgO films were prepared by using pulsed cathodic vacuum arc deposition technique. The substrate bias voltage was in the range of −150 to −750 V. Film structure was investigated by X-ray diffraction (XRD). The annealing effect of thermal spike produced by the impacting of energetic ions was analyzed. The calculated results showed that the lifetime of a thermal spike generated by an energetic ion with the energy of 150 eV was less than one picosecond and it was sufficient to allow Mg²⁺ or O^2- to move one bond length to satisfy the intrinsic stress relief in the affected volume. The MgO(200) lattice spacings of the films deposited at different bias voltages were all larger than the ideal value of 2.1056 Å. As the bias amplitude increased the lattice spacing decreased, which indicated that the compressive stress in the film was partially relieved with increasing impacting ion energy. The stress relief also could be reflected from the film orientation with bias voltage. The biaxial elastic modulus for MgO(100), MgO(110) and MgO(111) planes were calculated and they were M₍₁₀₀₎ = 199 GPa, M₍₁₁₀₎ = 335 GPa and M₍₁₁₁₎ = 340 GPa, respectively. The M values indicated that the preferred orientation will be MgO(200) due to the minimum energy configuration when the lattice strain was large. It was confirmed by the XRD results in our experiments.     

Structural and optical study of GaMnAs/GaAs

GaMnAs/GaAs was obtained with mass-analyzed low energy dual ion beam depostion technique with Mn ion energy of 1000 eV and a dose of 1.5 × 10¹⁸ Mn⁺/cm² at the substrate temperature of 400°C and was annealed at 840°C. X-ray diffraction spectra showed that Ga_5.2Mn, Ga₅Mn₈, -Mn and Mn₃Ga were obtained in the as-grown sample. After annealing Mn₃Ga and -Mn disappeared, Ga₅Mn₈ tended to disappear, Ga_5.2Mn crystallized better and new phase of Mn₂As was generated. The photoluminescence spectra of the as-grown sample showed that the 1.5042 eV GaAs exciton peak, 1.4875 eV peak involving a carbon acceptor and a broad band near 1.35 eV. After annealing at 840°C, the 1.5042 eV peak and 1.4875 eV shifted to 1.5065 and 1.4894 eV, respectively, and the photoluminescence intensity of the 1.35 eV band increased greatly.     

Influence of the self-buffer layer on ZnO film grown by atmospheric metal organic chemical vapor deposition

ZnO films with and without a self-buffer layer were grown on c-plane sapphire substrates by atmospheric metal organic chemical vapor deposition. The influence of the buffer layer thickness, annealing temperature and annealing time on ZnO films has been investigated. The full width at half maximum of the ω-rocking curve of the optimized self-buffer layer sample is only 395 arc sec. Its surface is composed of regular columnar hexagons. After the buffer layer was introduced, the A₁ longitudinal mode peak at 576 cm^− 1, related to the defects, disappears in Raman spectra. For the photoluminescence, besides the strong donor binding exciton peak at 3.3564 eV, an ionized donor binding exciton and a free exciton peak is respectively observed at 3.3673 and 3.3756 eV at the high-energy side in the spectrum of the sample with the buffer layer.     

YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next-Generation Laser-Driven Lighting

Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) transparent ceramic phosphors (TCPs) are regarded as the most promising luminescent converter for laser-driven (LD) lighting. High-quality YAG:Ce³⁺ TCPs are still urgent for high efficiency LD lighting devices. YAG:Ce³⁺ TCPs in a vacuum ambience by using nano-sized raw materials are prepared. Controlling defects by adding nano-sized MgO and SiO₂ simultaneously enables a high transmittance nearly 80%. After annealing in air furthermore, the luminous efficiency is enhanced greatly from 106 to 223 lm W⁻¹, which is the best result reported now for LD lighting. These results demonstrate that the optimizing YAG:Ce³⁺ TCPs in a fitting strategy will brighten once again in the next-generation LD lighting. Based on scanning electron microscopy (SEM) coupled with a cathodoluminescence system, defects and Ce³⁺ distributions in grains are identified directly for the first time.     

Investigation on deep level defects in rapid thermal annealed undoped n-type InP

Deep levels in rapid thermal annealed Pd/n-InP Schottky contacts have been studied using deep level transient spectroscopy. It is observed that the as-deposited Pd/n-InP Schottky sample exhibit two deep levels with activation energies of 0.53 and 0.70 eV. In samples annealed at 400 °C, three deep levels having activation energies 0.18, 0.30 and 0.86 eV below the conduction band are observed and for samples annealed at 500 °C, four deep levels with activation energies 0.33, 0.44, 0.70 and 0.82 eV are observed. Fourier transform infrared spectroscopy measurements have been carried out on undoped as-deposited and annealed InP wafers at 300, 400 and 500 °C. The measurements revealed high concentration of hydrogen complexes in the form of V_InH₄ existing in InP wafer. The results show that V_InH₄ complex annihilates with increase of annealing temperature and results in the formation of P _In ²⁺ and V _P ⁺ defects at 0.70 and 0.44 eV, respectively.     

DLTS study of annihilation of oxidation induced deep-level defects in Ni/SiO2/n-Si MOS structures

This paper describes the fabrication of MOS capacitor and DLTS study of annihilation of deeplevel defects upon thermal annealing. Ni/SiO₂/n-Si MOS structures fabricated on n-type Si wafers were investigated for process-induced deep-level defects. The deep-level traps in Si substrates induced during the processing of Ni/SiO₂/n-Si have been investigated using deep-level transient spectroscopy (DLTS). A characteristic deep-level defect at E _C = 0·49 eV which was introduced during high-temperature thermal oxidation process was detected. The trap position was found to shift to different energy levels (E _C = 0·43, 0·46 and 0·34 eV) during thermal annealing process. The deep-level trap completely anneals at 350°C. Significant reduction in trap density with an increase in recombination life time and substrate doping concentration as a function of isochronal annealing were observed.     

A comparative study of the electrical properties of reduced and unreduced LiTaO<Subscript>3</Subscript> crystals

We have carried out a comparative study of the electrical properties of lithium tantalate (LiTaO₃) crystals in a wide temperature range (300–900 K) before and after reductive treatment in H₂O vapor and subsequent oxidative annealing. The results demonstrate that, in the temperature range of Li⁺ ion conduction (550–900 K), the activation enthalpy for ionic conduction in the reduced lithium tantalate crystal is H _a = 1.37 eV, which slightly exceeds that in the initial state of the crystal (1.34 eV). In the temperature range 390–450 K, the σ(T) data for the unannealed crystal are well represented by the Arrhenius law in the presence of two carrier types, with activation energies E ₁ = 1.03 eV and E ₂ = 0.29 eV, characteristic of proton and electron hopping conduction, respectively. After reductive annealing, the activation energy for conduction is ~0.65 eV, characteristic of the activation energy for bipolaron conduction. After subsequent oxidative annealing of the reduced crystals in dry air, the activation energy is ~1.2 eV. It seems likely that the presence of oxygen vacancies in the reduced LiTaO₃ crystal stimulates hydrogen release from the crystal during oxidative annealing.     

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

ZnO is an efficient luminescent material in the UV-range ∼3.4 eV with a wide range of applications in optical technologies. Sputtering is a cost-effective and relatively straightforward growth technique for ZnO films; however, most as-grown films are observed to contain intrinsic defects which can significantly diminish the desirable UV-emission. In this research the defect dynamics and optical properties of ZnO sputtered films were studied via post-growth annealing in Ar or O₂ ambient, with X-ray diffraction (XRD), imaging, transmission and Urbach analysis, Raman scattering, and photoluminescence (PL). The imaging, XRD, Raman and Urbach analyses indicate significant improvement in crystal morphology and band-edge characteristics upon annealing, which is nearly independent of the annealing environment. The native defects specific to the as-grown films, which were analyzed via PL, are assigned to Zn_i related centers that luminesce at 2.8 eV. Their presence is attributed to the nature of the sputtering growth technique, which supports Zn-rich growth conditions. After annealing, in either environment the 2.8 eV center diminished accompanied by morphology improvement, and the desirable UV-PL significantly increased. The O₂ ambient was found to introduce nominal O_i centers while the Ar ambient was found to be the ideal environment for the enhancement of the UV-light emission: an enhancement of ∼40 times was achieved. The increase in the UV-PL is attributed to the reduction of Zn_i-related defects, the presence of which in ZnO provides a competing route to the UV emission. Also, the effect of the annealing was to decrease the compressive stress in the films. Finally, the dominant UV-PL at the cold temperature regime is attributed to luminescent centers not associated with the usual excitons of ZnO, but rather to structural defects.     

Preparation of MgO nano-rods with strong catalytic activity via hydrated basic magnesium carbonates

MgO nano-rods of several microns in length and 50–100 nm in width were prepared by calcining nesquehonite phase, obtained by simple precipitation using (NH₄)₂CO₃ under ambient condition. The MgO nano-rod with reasonably high surface area (75–120 m² g⁻¹) exhibits strong activity in solvent-free base catalyzed Claisen-Schmidt condensation giving 99% conversion in 2 h and is easily recyclable with no significant change in catalytic activity. Presence of numerous basic sites of different strengths (surface hydroxyl groups, low coordinate O²⁻ sites) is attributed to the observed effect.     

Atomic carbon in magnesium oxide Part VI: Electrical conductivity

In the range 300–1270 K the d.c. conductivity of high-purity arc-fused MgO single crystals was found to be very different during heating and cooling and after room temperature annealing. Measurements with and without guard ring and by the 4-point method gave essentially the same results. Two distinctly different activation energies were found: the 2.5 eV mechanism, already reported in the literature, which is characteristic for high temperatures, > 1000 K, and a 1.1 eV mechanism which progressively builds up in the 700–870 K interval during heating. Between 700–870 K the conductivity rises sharply and cooling yields 1.1 eV-branches which can be cycled many times. Room temperature annealing, however, destroys the 1.1 eV mechanism and leads again to sharply rising conductivity curves in the 700–870 K interval. Remarkable instabilities and occasional short circuiting phenomena were observed during cooling from temperatures slightly above 870 K. In this temperature region the conductivity reacted very fast to a change from Ar to O₂. Together with supporting evidence provided by other methods the conductivity behavior appears to be governed by the presence of atomic carbon in the MgO.     

Optical and dielectric properties of CuAl2O4 films synthesized by solid-phase epitaxy

The synthesis and properties of CuAl₂O₄ thin films have been examined. The CuAl₂O₄ films were deposited via reactive direct current magnetron sputter using a CuAl₂ target. As-deposited films were amorphous. Post-deposition annealing at high temperature in oxygen yielded solid-phase epitaxy on MgO. The film orientation was cube-on-cube epitaxy on (001) MgO single-crystal substrates. The films were transparent to visible light. The band gap of crystalline CuAl₂O₄ was determined to be ∼ 4 eV using a Tauc plot from the optical transmission spectrum. The dielectric constant of the amorphous films was determined to be ∼ 20-23 at 1-100 kHz.     

Defects in TiO2 films on p+-Si studied by positron annihilation spectroscopy

Variable-energy positron annihilation spectroscopy has been applied to the study of defects in TiO₂/p⁺-Si structures, in the as-grown state and after annealing in vacuum and in hydrogen, to investigate whether annealing (and film thickness) resulted in an increase of vacancy-type defects in the oxide films. It was found that the concentration of such defects remained unchanged after vacuum annealing for all films studied, but after H₂ annealing more than doubled for 150 nm-thick films, and increased by an order of magnitude for 100 nm-thick films. The nature of the vacancies was examined further by measuring high-precision annihilation lines and comparing them with a reference Si spectrum. The changes observed in the ratio spectra associated with oxygen electrons suggest that the defects are oxygen vacancies, which have been shown to enhance electroluminescence from TiO₂/p⁺-Si heterostructure-based devices.     

Defect-impurity complexes with high thermal stability in epi-Si n+-p diodes irradiated with MeV electrons

Defect-impurity complexes with high thermal stability which were generated after high temperature annealing of silicon n⁺-p diodes irradiated with 4 MeV electrons at 300 K have been studied by means of deep level transient spectroscopy (DLTS). Such defects are of interest because of their possible application in controlling the carrier lifetime in silicon power devices. The parameters of four deep level traps have been determined and compared with the results of photoluminescence studies on thermal stability of electron-irradiation-induced defects. A donor like trap with an energy level at E_v + 0.39 eV was assigned to a complex incorporating an interstitial carbon atom and two oxygen atoms (C_iO_2i), which gives rise to the P-line (hν = 0.767 eV) in photoluminescence spectra.     

The effect of annealing on the electroluminescence of SiO<Subscript>2</Subscript> layers with excess silicon

We have studied the effect of annealing on the electroluminescence (EL) spectrum of Si-SiO₂ structures containing excess ion-implanted silicon in the oxide layer. The implantation of 150-keV silicon ions to doses in the range from 5×10¹⁶ to 3×10¹⁷ cm⁻² leads to the appearance of an intense emission band at 2.7 eV in the EL spectrum. The postimplantation annealing leads to a decrease in the intensity of this band and to the appearance of a new EL band at 1.6 eV assigned to radiative transitions in defect centers formed at the boundaries between silicon nanoclusters and silicon dioxide.