Electrical characterization of impurity-free disordering-induced defects in n-GaAs using native oxide layers

Defects created in rapid thermally annealed n-GaAs epilayers capped with native oxide layers have been investigated using deep-level transient spectroscopy (DLTS). The native oxide layers were formed at room temperature using pulsed anodic oxidation. A hole trap H0, due to either interface states or injection of interstitials, is observed around the detection limit of DLTS in oxidized samples. Rapid thermal annealing introduces three additional minority-carrier traps H1 (E_V+0.44 eV), H2 (E_V+0.73 eV), and H3 (E_V+0.76 eV). These hole traps are introduced in conjunction with electron traps S1 (E_C-0.23 eV) and S2 (E_C-0.45 eV), which are observed in the same epilayers following disordering using SiO₂ capping layers. We also provide evidence that a hole trap whose DLTS peak overlaps with that of EL2 is present in the disordered n-GaAs layers. The mechanisms through which these hole traps are created are discussed. Capacitance–voltage measurements reveal that impurity-free disordering using native oxides of GaAs produced higher free-carrier compensation compared to SiO₂ capping layers. Received: 12 March 2002 / Accepted: 15 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +61-2/6125-0381, E-mail: pnk109@rsphysse.anu.edu.au     

Sequence of different types of nonlinear current oscillation in n-GaAs

In_xGa_1– xAs(x}<0.03)/GaAs lasers grown by vapor phase epitaxy using an In/Ga alloy source were characterized by double crystal X-ray (DCX) diffraction and deep level transient spectroscopy (DLTS) measurements. Based on the results obtained from (400), (511), and (¯511) DCX rocking curves, the obvious effect of In incorporation is to give an increase in the full width at half maximum of the rocking curves that correlates with a coherency of the epitaxial layers. From DLTS spectra according to the In content, the most prominent electron deep traps areE 4 (E _c-0.58eV) andE5 (E _c-0.84eV). TheE 4 trap density increases with In content while the change ofE 5 trap density is not monotonic. The trend ofE 5 trap densities versus In content is very similar to that of etch pit densities (EPDs), that is, a minimum in EPD andE 5 trap density is observed at an In content ofx0.003 but beyond this value the densities increase again with In content.     

On the mechanism of diffusion in sodium beta alumina

A microscopic interstitialcy-type diffusion mechanism for sodium beta-alumina involving three crystallographically different types of cation sites but only two equilibrium configurations of interstitialcy pairs is proposed. The resulting cation-site occupation probabilities are shown to agree with the experimental neutron-diffraction data of Roth et al. For various sizes of the associated regions around the charge-compensating oxygen interstitials (in which Na⁺ ions are not freely mobile), the ratio of the radiotracer diffusivity with respect to the charge diffusivity (the so-called Haven ratio, H_R)is determined. In agreement with the measurements of Kim et al.,H_R is found to increase with increasing temperature as a result of the decrease in the average size of the associated regions. It is concluded that, while at lower temperatures all excess Na⁺ ions are found in the associated regions around the oxygen interstitials, with increasing temperature more and more of them are freely mobile in the unassociated regions of the conduction plane. The formation enthalpy associated with the thermally activated creation of mobile “interstitials” is determined to be about 0.05 eV. The slope of the slightly curved Arrhenius plot associated with the proposed mechanism therefore consists of the sum of the energy of formation of freely mobile interstitials and the energies of migration of two types of interstitialcy pairs. The Raman and IR-conductivity results are found to be compatible with this emerging picture for the microscopic diffusion process in sodium β-alumina. Spectroscopic diffusion techniques (NMR, internal friction, dielectric loss) show more than one apparent activation energy E^A while, in the same temperature region, the d.c. ionic conductivity yields a unique value of E^A; reasons for this discrepancy are discussed.     

Energy features of bound polaron states in colored NaCl and KBr crystals

Thermoionization of bound polaron states in γ-irradiated KBr and NaCl crystals is studied in the temperature range 71–104 K. It is shown that the complex shape of the thermoionization curves in this temperature range is determined by the presence of three types of electron traps that are unstable (each trap decays according to an exponential law) and one type of stable trap. This explains a sharp break on the dependence of the logarithm of the lifetime on the reciprocal temperature, which is observed for a KBr crystal, as well as a number of discrepancies in the results obtained by other authors. The physical parameters (activation energy H for thermoionization, the optical absorption peak E _op, the spectral photoionization threshold E _i, and the energies of phonons participating in the optical absorption, L _op, and in photoionization, L _phc) obtained in the present paper and in our earlier studies on KCl, NaCl, and KBr crystals are analyzed, and the relations between these quantities predicted by available theories are considered.     

Study of non-exponential electron capture by the main electron trap in GaAs0.62P0.38

In deep level transient spectroscopy (DLTS) exponentiality of level population changes in thermal emission as well as in capture processes is assumed. This is however, contrary to what is often observed in experiment. In this paper a model for interpretation of DLTS data in the case of non-exponential capture of electrons is proposed. It is assumed that the height of the capture of carrier changes locally according to the Gaussian distribution This model is applied to the case of deep electron trap with thermal activation energy equal to ΔE_B = 0.39 eV, observed in VPE GaAs_0.62P_0.38. Te. This model provides a capture barrier as well as a capture cross-section which are different from the ones predicted by the exponential transient model i.e., the ones derived from the slope of capacitance changes due to the filling pulse versus pulse duration at very short times.     

The nature of the C-defects in nickel and their rôle in the interpretation of radiation damage in metals

In previous Perturbed-Angular-Correlation (PAC) studies of the - emission of ¹¹¹In probe nuclei in cold-worked or particle-irradiated nickel, it has been found that thermal annealing in the temperature regime of recovery stage III leads to the formation of so-called C-defects (Cubic defects). This is indicated by the occurrence of a new frequency of about 80 Mrad/s, in addition to the frequency (200 Mrad/s) that is due to ¹¹¹In on substitutional sites. Obviously, the C-defects are complexes consisting of ¹¹¹In and the intrinsic point-defect species that migrates freely in recovery stage III. Therefore, they have played an important rôle in the long-standing controversy on whether the recovery-stage-III defects are vacancies (one-interstitial model) or self-interstitials (two-interstitial model). The present paper reports on a novel experimental effort to reveal the nature of the C-defects by combining PAC studies on nickel samples differently pretreated in a systematic way, investigations of the Extended X-ray Absorption Fine Structure (EXAFS) on In-doped nickel, and measurements of the decay rate of ¹¹¹In nuclei in the Electron-Capture-Induced Decay (ECID). On the basis of the results of these experiments it is concluded that the defects trapped by substitutional ¹¹¹In atoms (In_s) in recovery stage III are self-interstitials (I), as expected according to the two-interstitial model. Moreover, there is evidence that the C-defects are In interstitials on tetrahedral sites (In_i) that form exclusively in the vicinity of the specimen surface from In_s – I pairs via the reaction In_s+I In_i.     

深能级陷阱对FET的光瞬态特性、等效噪声电流和漏电流升高的影响

本文基于位于准费密能级下深受主陷阱和剩余空穴,在平衡(无光照)和非平衡(有光照)条件下单位时间内空穴浓度变化率的微分方程基础上,导出了指数衰减理论方程,可很好地解释深能级对FET光脉冲瞬态特性的影响,指出了深能级是衰减长尾产生的根本原因,并测定了GaAs MESFET、GaAlAs TEGFET Si JFET的光脉冲瞬态特性,验证了理论模型的准确性。探讨了能级深度E_T等因素对衰减曲线的影响。测定了上述三类器件的等效噪声电压与频率f之间的关系,应用文献[6]的公式得出了相应的等效噪声 关键词：     

Resonant modes due to anion interstitials and anion vacancies in fluorites

The resonant modes due to anion interstitials and anion vacancies in fluorites are computed on the basis of a Green's function formalism. The Green's functions are calculated on the basis of shell model fitted to the phonon dispersion curves of the respective crystals. The force constant changes are calculated by finding the relaxations of the different host atoms and then using the short range potential due to Catlow and Norgett. The calculated frequencies of the resonant mode due to anion interstitials in BaF₂; shows good agreement with the experimental results. The results discussed in a comparative fashion for the three crystals CaF₂, SrF₂; and BaF₂; along with the possibility of their experimental detection.     

Sb complexes and Zn interstitials in Sb-implanted ZnO epitaxial films

In the present work, post-annealing is adopted to investigate the formation and the correlation of Sb complexes and Zn interstitials in Sb-ion implanted ZnO films, by using Raman scattering technique and electrical characterizations. The damage of Zn sublattice, produced by ion bombardment process is discerned from the unrecovered E2 (L) peak in annealed high Sb+ dose implanted samples. It is suggested that the Zn sublattice may be strongly affected by the introduction of Sb dopant because of the formation of SbZn-2VZn complex acceptor. The appearance of a new peak at 510 cm 1 in the annealed high dose Sb+ implanted samples is speculated to result from (Zn interstitials-O interstitials) Zni-Oi complex, which is in a good accordance with the electrical measurement. The p-type ZnO is difficult to obtain from the Sb+ implantation, however, which can be realized by in-situ Sb doping with proper growth conditions instead.     

Kinetics of crowdion reactions

The basic equations which govern diffusion-controlled reactions of crowdions (crowdion-vacancy annihilation, conversion of crowdions to dumbbell interstitials by means of crowdion-crowdion collisions, as well as conversion of crowdions at dumbbells and at impurities) are derived. ‘Off-line’ crowdions, which are unable to recombine with their ‘own’ vacancies, as well as ‘on-line’ crowdions, which anneal out preferentially in that way, are taken into account. Approaches to the solution of these equations are presented and compared with those found in the literature. In particular, an expression that was fitted successfully by Frank, Seeger, and. Schottky to the Corbett-Smith-Walker annealing data in stage I_E of electron-irradiated copper is rederived from the basic equations as an approximate solution for the regime of uncorrelated recovery. This means that the annealing kinetics in stage I_E of electron-irradiated copper may be explained in terms of the conversion-two-interstitial model.     

注氮GaAs中的深能级及其对自由载流子的补偿

详细研究了注氮n型GaAs中深的和浅的杂质缺陷的电学性质。深能级瞬态谱(DLTS)技术测量表明,能量为140keV和剂量为1×10¹³cm^-2的氮离子注入并经800℃退火30min的GaAs中存在四个电子陷阱,E₁(0.111),E₂(0.234),E₃(0.415),E₄(0.669)和一个空穴陷阱H(0.545),而在能量为20keV和剂量为5×10^{14关键词：}     

Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at E_v+0.128~eV, originates from the vacancy of Cd (V_Cd. The electron trap E1, found at E_c-0.178~eV, is considered to be correlated with the interstitial Cu_i⁼ in CdTe.     

Thermoluminescence kinetic study of binary lead-silicate glasses

This paper describes a detailed experimental study of the thermoluminescence (TL) properties of four binary lead-silicate glasses, with PbO concentrations ranging from 32% to 62% in mole percent. The TL glow peaks between room temperature and 300 °C were analyzed using a systematic thermal cleaning technique. The T_max-T_stop and E-T_stop methods of analysis were used to identify the number of peaks under the glow curves, and to obtain the activation energy E for each TL trap. A computerized glow curve fitting analysis is used to fit the experimental data to four first-order peaks with maxima at temperatures of 54, 80, 110 and 210 °C, as measured with a heating rate of 2 °C/s. The kinetic parameters of the glow-peak at 210 °C were confirmed by using phosphorescence decay methods of analysis. The TL traps associated with the low-temperature TL peak at 54 °C are found to depend strongly on the PbO concentration of the samples, while the higher-temperature TL peaks show a behavior independent of the PbO concentration. The activation energy E and frequency factor s of the low-temperature TL trap associated with the peak at 54 °C are consistent with a trap involving a delocalized transition through the conduction band. However, the activation energies and frequency factors for the higher-temperature TL traps are consistent with traps involving localized transitions via an excited state below the conduction band. The data suggest that these higher-temperature TL traps are associated with the common silicate matrix in these binary silicate glasses.     

A study of deformation-produced deep levels inn-GaAs using deep level transient capacitance spectroscopy

Deformation-produced deep levels, both of electron and hole traps, have been studied using deep level transient capacitance spectroscopy (DLTS) for an undopedn-type GaAs (HB grown) compressed at 440°C. Concentrations of two grown-in electron trap levels (E _c −0.65eV andE _c −0.74eV) and one grown-in hole trap level (E _v +∼0.4eV) increase with plastic deformation, while that of a grown-in electron trap level (E _c −∼0.3eV) decreases in an early stage of deformation. While no new peak appeared in the electron trap DLTS spectrum after plastic deformation, in the hole trap DLTS spectrum a broad spectrum, seemingly composed of many peaks, newly appeared in a middle temperature range, which may be attributed to electronic energy levels of dislocations with various characters.     

Isothermal capacitance transient spectroscopy (ICTS) study for midgap levels in Hb-GaAs by rapid thermal annealing

We studied the midgap levels by using isothermal capacitance transient spectroscopy (ICTS) in Hb-GaAs which had been processed by rapid thermal annealing (RTA). As the annealing time at 850 °C increased, the EL2 trap (E _c–0.81 eV) was transformed to the EX2 trap (E _c–0.73 eV) and eventually to the EX1 trap (E _c–0.87 eV). The diffusivity of the EL2 trap obtained from the experimental result of the heat treatment was about 1.02·10^–8cm²/s at 850 °C. This result indicate that the EL2 trap contains an interstitial arsenic atom. The result of the transformation to the EX1 and EX2 traps suggests that, when the EL2 trap is V_AsAS_iV_GaAs_Ga, the EX2 trap may be V_AsV_GaAs_Ga, which As_i is diffused out during a thermal annealing.     

Influence of Accelerator Content on Cure Kinetics of Sulfur-vulcanized Natural Rubber

Based on the cure characteristics of the NR/S/TBBS system, a kinetic model with induction, curing, and post-cure periods was chosen to simulate the cure reaction of this system. Cure curves reflecting the evolution of crosslink density were recorded as a function of curing time for NR compounds using a rubber processing analyzer (RPA). The cure curves were then non-linear fitted and the kinetic parameters were determined. The results showed that the simulated curves fit well with the experimental curves. As the concentration of activated sulfurating agents, A_o, increased, the activity of crosslink precursors increased (K₂ increased), while the activity for crosslinks to degrade decreased (K₆ decreased) due to shortening of the sulfur chain both in crosslink precursors and in crosslinks, leading to the improved thermal stability of NR vulcanizate at elevated temperatures. Increased accelerator amount also increased the competition of the reaction to form crosslinks over the reaction to form dead by-products, which improved the efficiency of sulfur. Reaction activation energy E₂ and E₆, calculated from K₂ and K₆ through the Arrhenius equation, showed that E₆ is higher than E₂. The increase of accelerator dosage led to the decrease of E₂ and increase of E₆, which explained the phenomenon of improved anti-reversion.     

Thermodiffusion of interstitials in a film

A general expression is obtained for the thermodiffusion coefficientD _T of a film, also for its dependence on temperature, film thickness and type of concentration distribution of the interstitials, according to its profile. In neglecting interaction of interstitials with each other in a model of a film with single-plane boundaries with the vacuum and the substrate, it is shown thatD _T>D _T ^(∞) is possible, whereD _T ^(∞) is the thermodiffusion coefficient of a bulk specimen. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 43–46, September, 1996.     

注硅半绝缘GaAs的深能级

用深能级瞬态谱(DLTS)详细研究了硅离子注入Liquid-encapsulated Czochralski(缩写为LEC)半绝缘GaAs的深中心。结果表明,在注硅并经高温退火的有源区中观测到4个多子(电子)陷阱,E₀₁,E₀₂,E₀₃和E₀₄。它们的电子表观激活能分别为0.298,0.341,0.555和0.821eV。其中E₀₄与EL2有关,但不是EL2缺陷。E₀₄的电子 关键词：