Annealing of γ-ray irradiated lithium compensated p-type silicon

Abstract

Annealing behavior of electrical properties and photoluminescence spectra both at 77 °K in electron-irradiated melt-grown n-GaAs were investigated. Defects electrically active in the Hall mobility and carrier removal anneal through two stages centered at 250° and 460 °K. From the temperature dependence of carrier concentration the existence of a defect level located near 0.15 eV below the conduction band is supposed. Several emission bands are resolved at 1.51, 1.47, 1.415, 1.305 and ～1.2 eV in photoluminescence experiments. Electron irradiation (1.5–2.0 MeV) causes a remarkable decrease in emission intensity of 1.51 and ～1.2 eV bands. Recovery of emission intensity occurs remarkably when samples are annealed to 520 °K which would correspond to the 460 °K annealing stage for carrier concentration and Hall mobility. The 250 °K annealing stage is not observed in photoluminescence experiments. The 1.415 eV peak appears clearly after irradiation and grows remarkably with the 520 °K annealing, especially in Si-doped samples, resulting in large reverse annealing. This band is tentatively speculated to be a complex of Si on As site with As vacancy. Moreover, in samples doped with Te a new emission band at 1.305 eV (9500 Å) is observed after 470°–620 °K annealing.     

Low-temperature electron radiation damage in scandium

Electron irradiation of hcp scandium at T ? 12 K allowed to determine the energy threshold for Frenkel-pair creation, T_d = 13.8 ± 0.5 eV, and the defect resistivity, $\text{?}{}_{\mathrm{<mtext>F</mtext>}}\text{≈ 5 × 10}{}^{\mathrm{?3}}\text{Ω}\text{cm/F.P}$. The annealing spectrum exhibits four substages between 20 and 70 K, a broad substage centered at 105 K attributed to interstitial long-range migration, and a stage III between 240 and 300 K.     

Dependence of photoluminescence from a-Si nanoparticles on the annealing time and exciting wavelength

Thin films of SiO_x having thickness of 0.2 μm and oxygen content x=1.5 or 1.7 are prepared by thermal evaporation of SiO in vacuum. Then some samples are furnace annealed for various times (in the range ) at 770 and 970 K and some others are rapid thermal annealed at 970 K for 30 and 60 s. Photoluminescence (PL) measurements are carried out at room temperature using the 442 nm line of a He-Cd laser and the 488 nm of an Ar laser for excitation. The effect of the annealing conditions and wavelength of the exciting light on the shape of the PL from these films is explored. The deconvolution of the PL spectra measured with the 442 nm line from samples annealed at 770 K for reveals two distinct PL bands peaked at around 2.3 and 2.5 eV, which do not shift appreciably with increasing annealing time. In addition, at longer annealing times, a weak third band is resolved centred in the range 2.0-2.1 eV. It exists in the spectra of all samples annealed at 970 K being more prominent in the samples with x=1.5. The intensity of this band shows different dependences on the annealing time in the films with different initial composition. The results obtained are discussed in terms of radiative recombination via defect states in the SiO_x matrix (the 2.5 eV band) or at the a-Si-SiO_x interface (the 2.3 eV band). The band centred in the 2.0-2.1 eV range is related to recombination in amorphous silicon nanoparticles grown upon annealing.     

F-Zentren und Kolloide in der amorphen,hexagonalen und kubischen Phase von LiJ

By simultaneous evaporation of LiI and Li onto a cooled substrate F centers can be produced in the hexagonal (78 K<T _K <200 K) and amorphous (T _K <78 K) phase of one and the same salt. In both modifications there exist two types of centers F and F^*. The F^* center differs from the cubic F center (T _d -symmetry) by a nearby Frenkel defect. In hexagonal films the normal F band peaks at 2.58 eV, whereas the transitions of the F^* center appear at 2.92 and 2.58 eV too. Polarized irradiation at 20 K causes a dichroic behaviour of the F^* centers. Both types of centers can be transformed into one another photochemically. In the amorphous phase all transitions are shifted to lower energies by about 0.1 eV. After the phase change amorphous→hexagonal the absorption bands shift back by the same amount of energy. AboveT _K =230 K the excess metal forms colloids. The absorption bands are due to colloidal centers embedded in the crystalline material (2.25 eV) and films adsorbed to the crystallites (3.1 eV), respectively. By annealing a particle growth can be observed. After electrolytic colouration cubic single crystals of LiI exhibit an absorption band peaking at 2.36 eV. However, it is not yet sure, if this band is allowed to be ascribed to F centers.     

Ultraviolet Luminescence Depending on Zn Interstitial in ZnO Polycrystalline Films

The ultraviolet emission line at 3.315eV is observed at 8K in ZnO polycrystalline films and investigated by temperature-dependent photolumineseence spectra and cathodoluminescence spatial image. The relative intensity of 3.315 eV emission line depends strongly on growth and annealing conditions. The cathodoluminescence image shows that the 3.315 eV emission localizes on the surface and ridge of ZnO grain. These results suggest that the 3.315 eV emission attributes to Zn interstitials at the grain surface and ridge. This emission is stable in the range from 8 K to 300 K and contributes to the room temperature ultraviolet band.     

Stimulated self-trapped exciton emission in CsI:Pb

Defects of the type of V_K and Pb⁺ centres were created in CsI:Pb under the 4.03 eV XeCl laser line irradiation at 10 K. After irradiation, the self-trapped and localized exciton emission excited by the same XeCl laser line was observed as a result of the recombination of electrons, optically released from Pb⁺, with the V_K centres. A strongly superlinear dependence of the emission intensity on the excitation intensity was found for the 3.65 eV emission of the self-trapped exciton. A much weaker superlinearity was observed for the visible localized exciton emission. Optical amplification of the exciton emission was considered as the most probable reason of the observed phenomenon. At 10 K, optical gain G=3.74 was calculated for the self-trapped exciton emission.     

Low temperature photoconductivity in electron - irradiated p-type Si

The photoconductivity spectra of p-type silicon irradiated at ～15 °K with 1.2 MeV electrons were studied in the wavelength range from 1.2 to 5.5 μ at temperatures from 23 to 80 °K. The 3.9 μ photoconductivity band appears immediately after irradiation in all crystals already at low temperatures, giving further evidence that it is due to the divacancy formed directly during irradiation by electrons. Three main annealing stages of the photoconductivity have been observed; (a) below 160 °K, (b) 160–250 °K, and (c) 280–360 °K. A radiation-induced deep level at E_v , +(0.12±0.02 eV disappears upon annealing at stage b. The annealing behavior of the spectra depends strongly on the measuring temperature. The dependence of the spectra on chopper speed was also investigated.     

X-ray irradiation enhanced critical current density and strong pinning sites created in Gd1Ba2Cu3O7−x thin films

An enhancement of the critical current density (to more than 10⁶ A/cm² below 65 K) of Gd₁Ba₂Cu₃O_7–x superconducting thin films was achieved by X-ray irradiation with oxygen annealing. This process of X-ray irradiation with oxygen annealing introduced stable pinning centers into the crystal and also increased the activation energy from 0.1 eV to 0.25 eV.     

Zn(0001) water interaction: An ultraviolet photoelectron spectroscopy investigation

The (0001) face of a Zn crystal has been exposed a ～300°K and at ～345°K up to 20.000L of water with no modification of the photoemission spectra at hν = 21.2 eV. Approximately one monolayer of reaction products is seen after condensing water at low temperature (～140°K) and desorbing it thermally. A broad peak at ～5 eV below Fermi level is seen and is attributed mostly to the formation of hydroxide.     

The defects produced by electron irradiation in tellurium-doped germanium

Abstract

The nature of the irradiation induced defects in germanium single crystal doped with tellurium was studied by DLTS and electrical measurements.

The E_c-0.21 eV level produced by irradiation with 1.5 MeV electrons was studied by DLTS technique. It was found that the defect associated with the E_c-0.21 eV level is divacancy. The E-center like defect (group V impurity-vacancy pair) introduces the E_c-0.20 eV level in samples doped with group V impurity. The level introduced by tellurium (group VI impurity)-vacancy pair is located at deeper than E_c-0.21 eV.

The E_c-0.16 eV level was generated by the annealing at 430 K. A model for the defect associated with the level is proposed to be a tellurium-vacancies complex.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Evidence for the existence of a complex isoelectronic center in Si : In

The effect of 1 MeV electron irradiation and a 100° annealing stage on the intensity of the U₂ line at 1.1182 eV is presented. Evidence is provided from intensity vs. excitation power measurements that the U₂ radiative recombination involves only a single exciton. Eight models are discussed, with a complex isoelectronic center being favored.     

Temperature dependence of the cathodoluminescence spectra of irradiated light-emitting-diode structures with multiple InGaN/GaN quantum wells

The cathodoluminescence spectra of regions of light-emitting structures with multiple InGaN/GaN quantum wells unirradiated and irradiated with an electron beam are investigated in the temperature range from liquid-nitrogen temperature to room temperature. It is shown that a new emission line with an energy of 2.69 eV emerges as a result of irradiation in addition to the initial 2.6 eV line. The intensity of the emission line associated with Mg in p-GaN also increases after irradiation.     

Investigation of interaction between lithium and tantalum under a silicon film coating by electron-stimulated desorption technique

The electron-stimulated desorption of Li⁺ ions from lithium layers adsorbed on the tantalum surface coated with a silicon film has been investigated. The measurements are performed using a static magnetic mass spectrometer equipped with an electric field-retarding energy analyzer. The threshold of the electron-stimulated desorption of lithium ions is close to the ionization energy of the Li 1s level. The secondary thresholds are observed at energies of about 130 and 150 eV. The threshold at an energy of 130 eV is approximately 30 eV higher than the ionization energy of the Si 2p level and can be associated with the double ionization. The threshold at 150 eV can be caused by the ionization of the Si 2s level. It is demonstrated that the yield of Li⁺ ions does not correlate with the silicon amount in near-the-surface region of the tantalum ribbon and drastically increases at high annealing temperatures. The dependence of the current of Li⁺ desorption on the lithium concentration upon annealing of the tantalum ribbon at T>1800 K exhibits two maxima. The ions desorbed by electrons with energies higher than 130 and 150 eV make the largest contribution to the current of lithium ions after the annealing. The yield of lithium ions upon ionization of the Li 1s level at an energy of 55 eV is considerably lesser, but it is observed at higher concentrations of deposited lithium. The results obtained can be interpreted in the framework of the Auger-stimulated desorption model with allowance made for relaxation of the local surface field.     

Effect of the annealing environment on the optical properties of ZnO/GaAs grown by MOCVD

The optical properties of ZnO grown on (1 0 0) GaAs substrate using metalorganic chemical vapor deposition are investigated by photoluminescence (PL) spectroscopy. Postgrowth annealing in nitrogen and oxygen was performed for different times and temperatures in order to incorporate As from the substrate into the ZnO thin films. The PL spectra of the samples annealed in different ambients reveal that the effect of As diffusion into the ZnO thin films is more pronounced when the annealing is performed in oxygen at 550 °C. The 11 K PL spectra show the appearance of a transition at ∼3.35 eV after annealing in oxygen at 550 °C for 1 h. A further increase in the annealing temperature leads to the disappearance of this line, while for annealing times longer than 2 h at 550 °C, it is no longer prominent. The increase in intensity of this new transition is also accompanied by the enhancement of radiative centers related to structural defects, such as the stacking fault-related transition at 3.31 eV and the Y-line. Temperature dependent PL illustrates the excitonic nature of the new transition at ∼3.35 eV, which is therefore assigned to (A⁰, X) transition, where the acceptor is possibly the 2V_Zn-As_Zn complex, with an activation energy E_A in the range of 160-240 meV. Furthermore, the enhancement of the radiative centers related to structural defects is regarded as evidence that As atoms tend to segregate in the vicinity of structural defects to relieve local strain.     

Temperature,injection level,and frequency dependences of the luminescence in lightly - and heavily-doped CdTe:In

The temperature dependence, injection level dependence, and modulation frequency response of cathodoluminescence have been measured in Te-rich CdTe:In for materials with In concentrations ranging from 3 × 10¹⁵cm^?3 to 1 × 10¹⁸cm^?3. In lightly-doped material, the 80 K luminescence shows sharp band-edge emission near 1.57 eV and a broad impurity-defect band near 1.4 eV. As temperature increases, the 1.4 eV band quenches out, leaving only the band-edge emission. In heavily-doped material, the band- edge emission is absent and the 80 K luminescence shows only the 1.4 eV band. As the temperature increases from 80 K to 300 K, the 1.4 eV band does not quench out but rather undergoes a complex evolution into a long tail on the band-edge emission which begins to appear at approximately 140 K. At a temperature of 200 K, where the luminescence of the heavily-doped material consists of a broad but structured band approximately 0.2 eV in width, frequency response measurements indicate that band-to-band transitions contribute to the high-energy part of the broad luminescence while the remainder of the band results from slower transitions. The frequency and temperature dependences suggest that the luminescence involves an impurity level that has merged with a band edge at an In concentration of $\text{1 × 10}{}^{18}\text{cm}{}^3$. We interpret this behavior as suggesting that the 1.4 eV luminescence in Te-rich CdTe:In results from a partially-forbidden transition between conduction band and a deep acceptor level rather than from an intracenter type of transition.     

The Hd-center interaction with a Rb+ ion during irradiation and thermal annealing in kBr

The role of Rb⁺ ions on defect formation in KBr has been studied. The impurity suppresses colorability due to X-raying at 6 K, but does not result in the formation of any centers characteristic to Rb⁺ ions at this temperature. A new optical absorption band peaked at 3.19 eV is produced only by thermal annealing of irradiated KBr:Rb. This band is annealed in parallel to the annealing of the F band in a stage at 55 K, obeying second-order rate equation with an activation energy of 0.102 eV. This band is ascribed to the H_A(Rb⁺)-center. Calculation is made on the elastic interaction energy between the H-center and a Rb⁺ ion, to show that the interaction along 〈110〉 is repulsive, whereas that along 〈001〉 is attractive. Based on this result of calculation, the structure and the formation mechanism of the H_A(Rb⁺) center, and origin of suppression of colorability at 6 K are discussed. The difference in the interaction of the interstitial atom with Rb⁺ during its dynamical motion and thermal motion is emphasized.     

Hole formation and charge transfer in Y1−xCaxSr2Cu2GaO7, a new oxide superconductor

The technique of transmission electron energy loss spectrometry (EELS) in parallel detection has been utilized to analyze the fine structures associated with the O K and Cu L₃ absorption edges of recently discovered Y_1−xCa_xSr₂Cu₂GaO₇ (0.1 ≤ x ≤ 0.4) series of compounds, which exhibit superconductivity when annealed under high-pressure oxygen atmosphere. We find subtle but significant changes in EELS spectral features of nonsuperconducting and superconducting specimens of these compounds. A broad pre-edge feature is observed below the O K absorption edge, at about 528.2 eV which emerges with Ca-doping alone. Evidence is presented for another O K secondary pre-edge feature, at about 1.1 eV below the first O K pre-edge feature in only those specimens which have undergone high-pressure oxygen treatment (i.e. superconducting specimens). We interpret the O K pre-edge feature as due to formation of holes on oxygen sites and propose that the first broad pre-edge feature (at 528.2 eV) is associated with holes on oxygen sites other than the CuO₂ planes, which are responsible for normal conductivity. The second smaller pre-edge feature (at 527.1 eV) is most probably associated with holes in the CuO₂ planes, which are associated with superconductivity in this system. The presence of a secondary smaller O K pre-edge feature in the superconducting specimens appears to correlate well with a broad shoulder on the high energy side of the Cu L₃ edge. The results are interpreted in terms of oxidation of CuO₂ planes through charge transfer between copper and oxygen in the CuO₂ planes, i.e. covalent mixing of O and Cu orbitals at the Fermi level as a result of high oxygen pressure annealing.     

退火对非故意掺杂4H-SiC外延材料386 nm和388 nm发射峰的影响

10 K条件下,采用光致发光(PL)技术研究了不同退火处理后非故意掺杂4H-SiC外延材料的低温PL特性.结果发现,在370—400 nm范围内出现了三个发射峰,能量较高的峰约为3.26 eV,与4H-SiC材料的室温禁带宽度相当.波长约为386 nm和388 nm的两个发射峰分别位于~3.21 eV和~3.19 eV,与材料中的N杂质有关.当退火时间为30 min时,随退火温度的升高,386 nm和388 nm两个发射峰的PL强度先增加后减小,且退火温度为1573 K时,两个发射峰的PL强度均达到最大. 关键词： 光致发光 退火处理 能级 4H-SiC     

Pseudo Stark and uniaxial stress splitting of the 6955 Å zero-phonon line in LiF

The spectral resolution of quartz crystals bent to a cylindrical form by means of four rods was investigated with CuKα radiation in a reflection type arrangement. The crystal adjustment was made optically using interference fringes. With the crystal bent to a circular cylinder the deviations from exact focusing inherent to the Johann case could be measured and were found to be in agreement with theory. — Crystals bent to a logarithmic spiral have also been studied. With a 24 mm broad reflecting area (mean radius of curvature 1 m; (13¯40)-plane) an uncorrected full width at half maximum intensity of 0.43 XU or 2.25 eV was observed for the CuKα ₁ line, in agreement with double crystal spectrometer measurements.