CdS/CdTe薄膜太阳电池的深能级瞬态谱和光致发光研究

用深能级瞬态谱和光致发光研究了无背接触层的CdS/CdTe薄膜太阳电池的杂质分布和深能级中心.得到了净掺杂浓度在器件中的分布.确定了两个能级位置分别在E_V+0365 eV和E_V+0282 eV的深中心,它们的浓度分别为167×10¹² cm^-3和386×10¹¹ cm^-2,俘获截面分别为143×10^-14cm²和153×10^-16cm².它们来源于以化学杂质形式存在的Au和（或）Te_Cd^-复合体,或与氩氧气氛下沉积CdTe时的氧原子相关. 关键词： 深能级瞬态谱 光致发光 CdS/CdTe太阳电池     

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     

Photoluminescence and capacitance transients in highly Mg-doped GaN

Behaviors of the photoluminescence blue-band and near-bandgap peak and the relevant thermal ionization energies of the shallow and deep Mg-related acceptors have been studied, respectively. The 2.989 eV blue-band is attributed to the deep donor–acceptor-pair transitions involving a deep Mg-related acceptor at E_v+0.427 eV. The blueshift with increasing excitation power is explained by variation in the contribution of close and distant donor–acceptor-pairs to the luminescence. The redshift with increasing temperature results from thermal release of carriers from close donor–acceptor-pairs. The 3.26 eV near-bandgap peak is attributed to the shallow donor–acceptor-pair transitions involving a shallow Mg-related acceptor at E_v+0.223 eV. The relevant thermal ionization energies of the shallow and deep Mg-related acceptors, being about E_v+0.16 and E_v+0.50 eV, are determined from deep-level transient Fourier spectroscopy measurements. Received: 11 July 2001 / Accepted: 9 August 2001 / Published online: 2 May 2002     

The electrical properties of zinc in silicon

Electrically active deep levels related to zinc in silicon are investigated in n- and p-type silicon using Deep-Level Transient Fourier Spectroscopy (DLTFS) measurements. While in n-type silicon a level at E _C–0.49 eV is observed, the main zinc-related levels in p-type silicon are determined to be E _V+0.27 eV and E _V+0.60 eV. The latter are associated with zinc situated on regular silicon lattice sites. The emission rate of these centers exhibits a field dependence which cannot be quantitatively explained with the Poole-Frenkel model. On the other hand, a shallow level at E _V+0.09 eV is observed only in boron-doped silicon which may be related to a zinc-boron complex. Other zinc-related levels are found at E _V+0.23 eV and E _V+0.33 eV, their concentration depending on that of zinc on substitutional sites. In addition, the evaluation of depth profiles and the analysis of the field dependence of the emission rate based on the DLTFS method is presented.     

不同温度下制备的CdTe薄膜对太阳电池光电性能的影响

在不同温度下用近空间升华法（CSS）制备了CdTe多晶薄膜,结合I-V,C-V特性及深能级瞬态谱研究了不同温度制备的CdTe薄膜对CdS/CdTe太阳电池性能的影响.结果表明,制备温度对电池组件的开路电压影响不大,对短路电流和填充因子有影响,CdTe薄膜的深中心对温度和频率的响应基本一致.580℃制备的样品暗饱和电流密度最小,载流子浓度较高,光电特性较好,而且空穴陷阱浓度较低,深中心复合作用较小.在此研究基础上制备出了面积为300 mm×400 mm 关键词： 制备温度 CdTe薄膜 深能级瞬态谱（DLTS） CdS/CdTe太阳电池     

Characterization of defects introduced in Sb doped Ge by 3 keV Ar sputtering using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS)

We have used deep level transient spectroscopy (DLTS), and Laplace-DLTS to investigate the defects created in antimony doped germanium (Ge) by sputtering with 3 keV Ar ions. Hole traps at E_V+0.09 eV and E_V+0.31 eV and an electron trap at E_C−0.38 eV (E-center) were observed soon after the sputtering process. Room temperature annealing of the irradiated samples over a period of a month revealed a hole trap at E_V+0.26 eV. Above room temperature annealing studies revealed new hole traps at E_V+0.27 eV, E_V+0.30 eV and E_V+0.40 eV.     

Transition metal impurities in silicon: New defect reactions

Recent investigations on transition-metal impurities in silicon emphasizing the effect of the combined diffusion of two transition metals are presented and briefly discussed. The electronic properties and basic thermal kinetics are analysed by DLTS. The conversion of a Pd-related multivalent defect atE _c-0.35 eV andE _c-0.57 eV to the Pd-related defect atE _c –0.22 eV is observed, and a Pd-Fe complex level atE _c –0.32 eV is identified. The annealing characteristics of the multivalent Rh levels atE _c-0.33 eV andE _c-0.57 eV are observed, and used to analyse the influence of prior Rh doping on the Au diffusion. A complex formed by the codiffusion of Au and Cu is observed atE _v+0.32eV andE _v+0.42 eV, and shown to exhibit bistable behavior as does a similarly produced Au-Ni complex observed atE _v + 0.35 eV andE _v+0.48 eV.     

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.     

Concentrations of radiation defects with almost isoenergetical levels in silicon

Isochronous annealing of radiation defects with almost isoenergetical levels (indistinguishable from each other by means of temperature dependence of the majority charge carriers concentration) in silicon is studied. The concentrations of G- and A-centres with a level E _c?0.17 eV in n-Si and some (unidentified) vacancy-type and V₂+B complexes with a level E _v+0.22 eV in p-Si are determined.     

Deep levels in low‐energy electron‐irradiated 4H‐SiC

Deep levels introduced by low‐energy (200 keV) electron irradiation in n‐type 4H‐SiC epitaxial layers grown by chemical vapour deposition were studied by deep level transient spectroscopy (DLTS) and photoexcitation electron paramagnetic resonance (photo‐EPR). After irradiation, several DLTS levels, EH1, EH3, Z_1/2, EH5 and EH6/7, often reported in irradiated 4H‐SiC, were observed. In irradiated freestanding films from the same wafer, the EPR signals of the carbon vacancy in the positive and negative charge states, V_C⁺ and V_C^‐, respectively, can be observed simultaneously under illumination with light of certain photon energies. Comparing the ionization energies obtained from DLTS and photo‐EPR, we suggest that the EH6/7 (at ～E_C – 1.6 eV) and EH5 (at ～E_C – 1.0 eV) electron traps may be related to the single donor (+ | 0) and the double acceptor (1– | 2–) level of V_C, respectively. Judging from the relative intensity of the DLTS signals, the EH6/7 level may also be contributed to by other unidentified defects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the validity of the amphoteric-defect model in gallium arsenide and a criterion for Fermi-level pinning by defects

Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, anamphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancyV _Ga ^2– and the triply positively charged defect complex (AS_Ga+V _As)³⁺, with As_Ga being the antisite defect of an As atom occupying a Ga site andV _As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect systemV _Ga ^2– /(As_Ga+V _As)³⁺ is supposed to be able to pin the GaAs Fermi level at approximately theE _v +0.6 eV level position, which requires that the net free energy of theV _Ga/(As_Ga+V _As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about theE _v +1.2 eV level position instead of the neededE _v +0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future.     

Trap centers in Au-implanted MOS structures

Trap centers in the Si-SiO₂ interface region of MOS structures doped by ion implantation of gold have been investigated using constant capacitance deep level transient spectroscopy (CC-DLTS). Gold doses of 10¹²–3 × 10¹³ cm^–2 were implanted into the back surface of the wafers and were then redistributed during a diffusion anneal for 30 min at 1100° or 900° C. Three Au-related trap levels have been observed in the interface region, which were attributed to the Au-donor (E _v +0.35 eV), the Au-acceptor (E _v +0.53 eV), and the Au-Fe complex (E _v +0.45 eV). The trap concentration profiles show that the Si-SiO₂ interface affects the Au concentration in a depth range of 1 m from the interface and that gettering of Au occurs at the interface. The interface state density is independent of the Au concentration at the interface even for concentrations of 10¹⁵ cm^–3.     

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.     

Studies of annealing of point defects and their influence on the electrical degradation and recovery behaviors of heavily neutron irradiated silicon

We have investigated the annealing behaviors of point defects and their influence on the electrical degradation and recovery of heavily neutron irradiated silicon. It is found that high concentrations of divacancy (V₂) and vacancy-oxygen (VO) complexes are introduced in heavily irradiated silicon, which is responsible for the enhanced carrier recombination and therefore the observed drastic decrease of carrier lifetime. While the dopants deactivation from vacancy-phosphorus (VP) complexes and carrier compensation from VO and V₂ complexes result in the remarkable increase of resistivity. After post-irradiation isochronal annealing at 200–400°C the carrier lifetime and resistivity exhibit insignificant changes, which is attributed to the transformation of V₂ and VO complexes into [VO?+?O_i], V₂O, V₃O complexes at 200–300°C and the possible formation of VP-O complexes at 400°C. While the heat treatments at elevated temperatures (>400°C) result in the elimination of the majority of electrically active V_mO_n and the possible VP-O complexes, and therefore the carrier lifetime and resistivity of silicon begin to recover at 500°C and 650°C, respectively. However, the recovery of carrier lifetime is incomplete, which is due to the enhanced carrier-recombination from the survival defects with deep levels at E_C ? 0.24?eV and E_C ? 0.44?eV during annealing.     

Photoelectric phenomena and photoluminescence in epitaxial CdSe thin films

Photoelectric phenomena and photoluminescence (static characteristics) were studied in epitaxial CdSe thin films built up on sapphire and fluorite substrates in a feedthrough CdSe-H₂ gas-transport system. It has been established that the spectral pattern of the extrinsic luminescence and photosensitivity in epitaxial films is determined by the common centers E_V+0.06, E_V+0.27, e_v+0.48 and E_V+0.60 eV. The presence of such centers also explains the trends which the temperature characteristics of the photocurrent follow, the spectral pattern of infrared quenching, and the lux-ampere characteristics of these films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 61–66, March, 1975.     

<Emphasis Type="Italic">I-V,C-V</Emphasis> and deep level transient spectroscopy study of 24 MeV proton-irradiated bipolar junction transistor

This paper describes the effect of 24 MeV proton irradiation on the electrical characteristics of a pnp bipolar junction transistor 2N 2905A. I-V, C-V and DLTS measurements are carried out to characterize the transistor before and after irradiation. The properties of deep level defects observed in the bulk of the transistor are investigated by analysing the DLTS data. Two minority carrier levels, E _C − 0.27 eV and E _C − 0.58 eV and one majority carrier level, E _V +0.18 eV are observed in the base collector junction of the transistor. The irradiated transistor is subjected to isochronal annealing. The influence of isochronal annealing on I-V, C-V and DLTS characteristics are monitored. Most of the deep level defects seem to anneal out above 400°C. It appears that the deep level defects generated in the bulk of the transistor lead to transistor gain degradation. A comparison of proton- and electron-induced gain degradation is made to assess the vulnerability of pnp transistor as against npn transistors.     

The effective-mass nature of deep-level point-defect states in semiconductors

The basic premise of Effective-Mass Theory (EMT) is that bound-state wavefunctions are constructible from Bloch functions in a small region or regions of k space. In contrast, deep-level wavefunctions are believed to involve Bloch functions from the entire Brillouin zone and several bands. In this paper we analyse the wavefunction of the deep vacancy level in Si obtained recently by self-consistent Green's-function calculations. We find that this wavefunction has a strong EMT character in that it is composed primarily of Bloch functions from the nearest bands and the corresponding coefficients, i.e. the envelope functions, are peaked about the band extrema. As a further check, we have used a spherical average of the self-consistent vacancy potential in the acceptor EMT equations. The resulting energy level is at E_v+0.9 eV, as compared with the Green's-function-theoretic value of E_v+0.8 eV. The resulting wavefunction, on the other hand, does not have the correct form. A check of the correction terms left out by the standard EMT equations reveals that their contributions to the energy level are large and tend to cancel one another.     

Properties of single vacancies and of divacancies in copper

The electrical resistivity change at high temperatures due to vacancies was determined as a function of temperature. From the data E^F_1V=1.00 eV, E^B_2V=0.45 eV and about C^tot_V=4 × 10^-4 at the melting point results.     

Investigation of the electrophysical properties and structures of impurity-defective complexes in silicon doped with palladium

Electric and structural methods are used to investigate formation of impurity-defective complexes in silicon doped with palladium. It is demonstrated that acceptor levels E _C – 0.18 and E _v + 0.34 eV detected in silicon during incorporation of palladium are caused by singly and doubly negatively charged states of [Pd–V] complexes, and the donor level E _v + 0.32 eV is a product of chemical compound of palladium with hydrogen forming the [Pd–H] complex. It is assumed that the palladium impurity in the doped silicon samples causes the elastic crystal energy to change and impurity clouds to be formed around microdefects. An increase in the temperature of palladium diffusion in silicon causes the impurity clouds to decay and the microdefect core sizes to decrease with their subsequent chaining into a needle.     

Boron-related deep centers in 6H-SiC

6H-silicon carbide layers are grown by a liquid phase epitaxy (LPE) process. The layers are doped with boron either by ion implantation or during the LPE process from a B-doped silicon melt. Deep-level transient spectroscopy (DLTS), admittance spectroscopy and photoluminescence (PL) are used to investigate deep impurity centers. Two electrically active defect centers are detected: the isolated boron acceptor at E _B=E _v+0.3eV and the boron-related D-center at E _D=E _v+0.58eV. The yellow luminescence observed in these layers is proposed to be due to pair recombination via D-center and nitrogen donor. Formation and origin of the D-center are discussed.