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.     

硅中三空位V3-的超精细相互作用的理论计算

利用Koster-Slater的格林函数方法,计算了硅中三空位V₃^-的电子态能级和波函数.结果表明,V₃^-在禁带中有五条能级:E_(A2)=0.417eV,E_(B1)=0.492eV,E_(B2¹)=0.512ev, E_(A1)=0.532eV,E_(B2²)=0.608eV.根据算得的超精细相互作用常数同实验值的比较,定出V₃^-处于B₁态.V₃^-的B₁态点据第1壳层的几率为60.2％,但主要集中在三空位所确定的平面内的二个原子上. 关键词：     

Luminescence response of CsI:Na to electron pulse irradiation

This paper investigates the influence of activator concentration and temperature on the scintillation process in CsI:Na crystal which was excited by a pulsed electron beam (E_ex = 0.25 MeV, t_1/2 = 15 ns, W = 0.003…0.16 J/cm²) at temperature within 77–300 K. It has been established that the transition of Na-bound two halide exciton from singlet state causes 3 eV emission of CsI:Na. The capturing of V_k by Na⁺ ion determines the scintillation pulse shape. Thermal liberation of V_k from V_kA centers results in an inertial rise of the emission pulse in lightly activated CsI:Na and in a mono-exponential decay of the emission pulse in heavily activated CsI:Na. The value of thermal dissociation energy of V_kA centers is 0.24 ± 0.01 eV, which was obtained from the temperature dependences of the emission decay time constant for CsI:2.8∙10⁻³%Na and of the rise time constant for CsI:2.0∙10⁻⁴%Na.     

Influence of deformation on the conductivity and photoconductivity of p-Type CdTe

Samples of p-type CdTe were subjected to deformation. Studies were performed of the influence of 60°-dislocations on the electrical conductivity, on the lifetime of minority carriers and on the relative change of the conductivity due to illumination. Dislocations were produced by bending the sample that was cut at suitable orientation. In this way, one obtained the 60°-dislocations, either of α- or β-type, according to the kind of bending involved. From the measurement of the temperature dependence of the conductivity it was ascertained that an increase in acceptor concentration occurs on the level with activation energy of 0.3 eV (identical to that of V^cd or a complex with V^cd), regardless of the type of dislocations. The concentration of acceptors on the level with activation energy 0.3 eV increases on increasing the dislocation density. The most probable explanation is that the deformation and, especially, annealinginduced migration of the dislocations produced give rise also to V^cd and/or V^Te (both types simultaneously). V^cd acts as an acceptor and V^Te as a donor. It follows that the increase in V^Te can not be established from this measurement. The lifetime of the minority carriers is almost unaffected by introducing the dislocations into the samples. From the temperature dependence of the relative change in conductivity due to illumination one can determine the activation energy of a dislocation level provided that one assumes the dislocations acting as recombination centers. Under this assumption one obtainsE _d =0.21–0.24 eV (for type α) andE _d =0.55–0.59 eV (for type β), measured from the top of the valence band.     

Room temperature photoluminescence from Zr-doped sol-gel silica

Intense room-temperature photoluminescence (PL) from the UV to the green region was observed from Zr⁴⁺-doped silica synthesized by a sol-gel process using tetraethoxysilane as the precursor, followed by thermal treatment at 500 °C in air. The wide PL band can be resolved into three components centered at 3.70, 3.25, and 2.65 eV, respectively. The intensity of the 3.25 and 2.65 eV PL bands was greatly enhanced compared with pure sol-gel silica. The 3.70 eV emission was assigned to non-bridging oxygen hole centers, while the 2.65 eV one originated from neutral oxygen vacancies (V_O). The 3.25 eV PL band was most likely associated with E′ centers, as supported by electron spin resonance measurement. It was proposed that the Zr⁴⁺-doping leads to oxygen deficiency in the silica, thus resulting in enhancement of the density of V_O and E′ center defects.     

Relation between interface states and temperature behavior of the barrier height of silver contacts on clean cleaved n-type silicon

The properties of silver-silicon interfaces formed by cleaving n-type silicon in ultra high vacuum (UHV) in a stream of evaporating silver atoms were studied. The barrier heights of these contacts were measured at different temperatures by using C-V techniques. All measurements were performed in UHV. The dependence of the barrier height upon temperature did not follow the temperature dependence of the Si band gap as it is usually found. The measured temperature behavior depended on the roughness of the Si surface. The temperature behavior can be explained by assuming a specific band structure of the interface states. For Ag contacts on atomically smooth n-type Si, the interface states were found to be arranged in two bands, one band 4 × 10^?3 eV wide with acceptor type states 0.18 eV below the intrinsic level E_i and a density of 10¹⁷ states/cm² eV, and the other 1 eV wide with donor type states with its upper edge 0.28 eV below E_i, and a density of 4 × 10¹⁴ states/cm²eV.     

A tunneling spectroscopy study of the temperature dependence of the forbidden band in Bi2Te3 and Sb2Te3

Tunneling measurements of dI/dV, d ² I/dV ², and d ³ I/dV ³ were formed along the C ₃ axis (normally to layers) for Bi₂Te₃ and Sb₂Te₃ layered semiconductors in the temperature range 4.2<T>29 5 K. Temperature dependences of the forbidden band energy E _g were obtained. The forbidden band energy in Bi₂Te₃ was 0.20 eV at room temperature and increased to 0.24 eV at T=4.2 K. The E _g value for Sb₂Te₃ was 0.25 eV at 295 K and 0.26 eV at 4.2 K. The distance between the top of the higher valence band of light holes and the top of the valence band of heavy holes situated lower was found to be ΔE _V≈19 meV in Bi₂Te₃; this distance was independent of temperature. The conduction bands of Bi₂Te₃ and Sb₂Te₃ each contain two extrema with distances between them of ΔE _c≈25 and 30 meV, respectively.     

Analysis of current–voltage and capacitance–voltage characteristics of perylene-monoimide/n-Si Schottky contacts

The electrical and interface state properties of Au/perylene-monoimide (PMI)/n-Si Schottky barrier diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements at room temperature. A good rectifying behavior was seen from the I–V characteristics. The series resistance (R_s) values were determined from I–V and C–V characteristics and were found to be 160 Ω and 53 Ω, respectively. The barrier height (Φ_b) of Au/PMI/n-Si Schottky diode was found to be 0.694 eV (I–V) and 0.826 eV (C–V). The ideality factor (n) was obtained to be 4.27 from the forward bias I–V characteristics. The energy distribution of interface state density (N_ss) of the PMI-based structure was determined, and the energy values of N_ss were found in the range from E_c ? 0.508 eV to E_c ? 0.569 eV with the exponential growth from midgap toward the bottom of the conduction band. The values of the N_ss without R_s are 2.11 × 10¹² eV^?1 cm^?2 at E_c ? 0.508 eV and 2.00 × 10¹² eV^?1 cm^?2 at E_c ? 0.569 eV. Based on the above results, it is clear that modification of the interfacial potential barrier for metal/n-Si structures has been achieved using a thin interlayer of the perylene-monomide.     

Local density valence band offset in GaAs/AlAs: Role of interface dipole

The valence band offset, ΔE_V ,at the lattice-matched GaAs/AlAs(001) interface is derived from highly precise self- consistent all-electron local density band structure calculations of the (GaAs)_n(AlAs)_n(001) superlattices (with n ⩽ 3). Using the core levels as reference energies, we find that ΔE_V = 0.50 ± 0.05 eV, in very good agreement with recent experimental results (ΔE_V = 0.45 − 0.55 eV). The dependence of ΔE_V on the superlattice thickness is studied and related to the interface charge redistribution which produces an interface dipole potential estimated to be ∼ 0.14 eV.     

Correlations between the arrival directions of ultrahigh energy cosmic rays and the large-scale structure of the universe

We present the results of analyzing the arrival directions of cosmic rays with energies E ₀≥ 4×10¹⁷ eV and zenith angles θ≤45° detected at the Yakutsk setup during 1974–2000. It is shown that increased particle fluxes exceeding the anticipated random distribution levels by 4–5)σ arrive from the galactic plane at E ₀≈(2–4)×10¹⁸ eV and from the supergalactic plane at E ₀≥8×10¹⁸ eV.     

The temperature dependence of optical gap and photoconductivity threshold in undoped hydrogenated amorphous silicon films

We report on the temperature dependences of the optical gap E_o and the photoconductivity threshold (?ω)_o for undoped hydrogenated amorphous silicon films. When increasing the temperature, both E_o and (?ω)_o are seen to linearly decrease at respective rates β= 3.5 10^?4 eV K^?1 (temperature range 290 K–460 K) and γ= 5.2 10^?4 eV K^?1 (temperature range 220 K – 360 K). At higher temperatures E_o decreases at the rate β = 14.3 10^?4 ev K^?1. Our results are discussed in terms of conduction in extended states. We show there is no physical reason in relating the temperature dependence of the activation energy and that of the gap as generally assumed. From optical absorption we deduce a minimum metallic conductivity σ_min the value of which agrees with Mott's predictions. On the contrary, σ_min measured from dark conductivity is nearly two orders of magnitude lower. A discussion is proposed infering band bending at the film substrate interface.     

Short-living absorption and emission of CsI(Na)

This paper investigates the short-living absorption and the emission of CsI(Na) under a pulsed electron beam (Е_e=0.25 MeV, t_1/2=15 ns and W=0.003…0.16 J/cm²). The bands of singlet self-trapped excitons, as well as Na⁰ and V_k color centers have been detected in the transient absorption spectrum of CsI(Na). It has been found that the activator luminescence spectrum, peaking at 3.0 eV, fits a Gaussian (E_m=3.0 eV and FWHM=0.44±0.02 eV at 80 K) and remains the same at different time delays within 10⁻⁸-10⁻³ s. The decay kinetics of the 3.0 eV emission has one nanosecond exponential component and two microsecond ones with time constants 1.0 and 3.0 μs, which remain unchanged within 78-150 K. It is concluded that the activator emission is due to the radiative annihilation of sodium-perturbed two halide excitons from the non-relaxed singlet state. The pathways of such excitons creation are discussed.     

Estimation of the energy of the electron-photon component of cosmic rays on the basis of data for Cherenkov light from ultrahigh-energy extensive air showers

The energy fraction E _em/E ₀ dissipated to the electron-photon component of extensive air showers (EASs) for E ₀=10¹⁵?10¹⁹ eV is estimated using data on Cherenkov radiation and charged particles from the Yakutsk EAS array. The results are compared with models with different dissipations to the electron-photon component and with calculations for various primary nuclei. In the energy range 10¹⁵?10¹⁶ eV and 10¹⁸?10¹⁹ eV, the ratio E _em/E ₀ is equal to 77 ± 2 and 88 ± 2, respectively, in agreement with the mixed and proton contents of primary cosmic rays in the former and latter energy ranges, respectively.     

Deep level transient spectroscopy in Hg1−xCdxTe

We report the application of Deep Level Transient Spectroscopy (DLTS) in Hg_1-xCd_xTe, demonstrating for the first time the utilization of DLTS techniques in a narrow band-gap semiconductor, E_g < 0.40 eV. DLTS measurements performed on an n⁺-p diode with E_g (x=0.21, T=30 K) =0.096 eV have identified an electron trap with an energy of E_v + 0.043 eV and a hole trap at E_v + 0.035 eV. Measurements of trap densities, capture cross sections, and the close proximity of the electron and hole trap locations within the band-gap suggest that DLTS may be observing both the electron and hole capture at a single Shockley-Read recombination center. The trapping parameters measured by DLTS predict minority carrier lifetime versus temperature data to be comparable with the experimentally measured values.     

Low energy excitations in KMnO4 with 1 eV<=ΔE<=10 eV from electron-energy loss spectroscopy

Electron-energy loss spectra of potassium permanganate (KMnO₄) with primary electron energies 25 eV<=E₀<=500 eV show 7 peaks in the energy-loss range 1 eV<=ΔE<=10eV and are successfully analysed with a superposition of 7 independent Gaussians. The intensity of these lines follow roughly a power-law dependence on the primary energy I∝E ₀ ^-α . There are two groups of lines, the first with an exponent α≈0.5, while the lines in the second group decay much stronger with increasingE ₀ corresponding to a value 0.9<=α<=1.3. The 4 lines in the first group are identified as dipole allowed transitions by comparison to recent first principle molecular-orbital calculations for the (MnO₄) molecule by H. Nakai et al. The dipole-allowed excitation spectrum obtained from this analysis agrees very well with these first principle calculations.     

Carbon segregation on a tungsten surface

New measurements are performed and a comprehensive analysis of experimental data is made on the dependence of equilibrium carbon coverage θ on a tungsten surface on its temperature and the degree of carbon loading. It is shown that if the volume is free of carbon, the variation of θ for T≥1400 K can be approximately described by the balance between the carbon flows through the boundary with the activation energy for transition into the bulk E₁=4.6 eV and the segregation energy ΔE=1.7 eV. For tungsten loaded preliminarily with carbon to a content of ≈10^?2 at. %, the θ(T) relation cannot be described in terms of the equilibrium conditions with constant E₁ and ΔE, because these quantities depend on the degree of carbon loading; E₁ grows from 4.6 to 6.8 eV and ΔE grows from 1.7 to 2.3 eV with an increase in carbon content from 0 to 10^?2 at. %. These variations are attributed to the bonds becoming stronger in carbon-loaded tungsten with increasing carbon content.     

Deep level transient spectroscopy (DLTS) study of defects introduced in antimony doped Ge by 2 MeV proton irradiation

Deep level transient spectroscopy (DLTS) and Laplace-DLTS have been used to investigate the defects created in Sb doped Ge after irradiation with 2 MeV protons having a fluence of 1×10¹³ protons/cm². The results show that proton irradiation resulted in primary hole traps at E_V +0.15 and E_V +0.30 eV and electron traps at E_C ?0.38, E_C ?0.32, E_C ?0.31, E_C ?0.22, E_C ?0.20, E_C ?0.17, E_C ?0.15 and E_C ?0.04 eV. Defects observed in this study are compared with those introduced in similar samples after MeV electron irradiation reported earlier. E_C ?0.31, E_C ?0.17 and E_C ?0.04, and E_V +0.15 eV were not observed previously in similar samples after high energy irradiation. Results from this study suggest that although similar defects are introduced by electron and proton irradiation, traps introduced by the latter are dose dependent.     

CeAlO<Subscript>3</Subscript> crystals: Preparation and study of their electrical and optical characteristics

Crystals of cerium aluminate with perovskite structure were obtained using the cold-crucible technique. The electrical and optical properties of cerium aluminate were studied in air in the range 300–1300 K. The main characteristics of CeAlO₃ at T=300 K are a follows: electrical conductivity σ=10^?7 S/cm, dielectric permittivity ?=3000–10000 (both measured at a frequency of 1000 Hz), thermal band-gap width ΔE=2.3±0.5 eV, and optical width δE=2.65±0.25 eV, which decreases at a rate of ?0.62×10^?3 eV/K with increasing temperature in the 300-to 1500-K interval.     

Dipole reorientation from bound-polaron hopping in single crystal NiO

We report observation of a first order thermal depolarization peak at 190 K in NiO single crystals which we attribute to the reorientation of Ni³⁺Ni_V²⁺ dipoles. Analysis of the data in terms of these bound polarons, using a non-adiabatic hopping model, yields values of activation energy, E = 0.31eV and the polaron band width, J = 8.6 × 10^?6 eV.     

Experimental determination of valence band offset at PbTe/Ge(1 0 0) interface by synchrotron radiation photoelectron spectroscopy

The band offset at the interface of PbTe/Ge (1 0 0) heterojunction was studied by the synchrotron radiation photoelectron spectroscopy. A valence band offset of ΔE_V = 0.07 ± 0.05 eV, and a conduction band offset of ΔE_C = 0.27 ± 0.05 eV are concluded. The experimental determination of the band offset for the PbTe/Ge interface should be beneficial for the heterojunction to be applied in new optoelectronic and electronic devices.