多孔氧化铝薄膜的光致发光起源:三种缺陷中心

在草酸溶液中用二次阳极氧化法制备了纳米多孔氧化铝薄膜,分析了制备过程中氧化铝薄膜中缺陷的形成机理.场发射电子显微镜给出了薄膜的表面形貌和结构.X射线色散能谱和傅里叶红外透射光谱测试表明,进入薄膜中的草酸杂质加热到500℃未全部分解.对多孔氧化铝薄膜的光致发光PL光谱做了高斯拟合,结合测试结果和薄膜中的缺陷分析指出:多孔氧化铝薄膜的发光由F+,F和草酸杂质相关缺陷引起,对应发光中心分别在402,433,475 nm处,并提出F中心起主导作用.对不同草酸浓度中制备的多孔氧化铝薄膜的PL光谱讨论指出:随草酸浓度增加,三种发光中心的峰位不会发生变化,但相对强度发生改变,F+中心和F中心减少,草酸杂质相关发光中心增加,PL峰红移.最后提出通过控制草酸浓度来控制多孔氧化铝薄膜中的草酸杂质.此研究将对多孔氧化铝薄膜发光起源和机理有更深入的理解,同时也为多孔氧化铝薄膜的制备提供一种全新的思路.     

Ti/Al p-GaN Schottky barrier height determined by C–V measurements

Data are presented on the rigorous method of capacitance–voltage (C–V) measurements to the barrier height of Ti/Al p-GaN Schottky junction. For a sample with Hall concentration of 5.5 × 10¹⁶/cm³ the upper limit of the modulation frequency leading the full response of the activated carriers is defined as 1.5 kHz from the capacitance versus modulation frequency (C–f) plot. The activation energy of the Mg acceptors determined from the temperature-dependent C–f plot is 0.12 eV. The barrier height estimated with this activation energy and the intercept voltage of the 1/C²–V plot drawn with the 1.5 kHz C–V data is 1.43 eV at 300 K and 1.41 eV at 500 K. This is the most reliable barrier height ever reported. A reliable room temperature C–V doping profile is demonstrated using the 1.5 KHz modulation, which is sensitive enough to resolve the presence of a 15 nm thin highly doped (8 × 10¹⁸/cm³) layer formed near the surface.     

Exciton mechanism of energy transfer to F-centers in dosimetric corundum crystals

The optical absorption (OA) and thermoluminescence of oriented -Al₂O₃ crystals colored in aluminum vapor have been studied. Optical absorption measurements of an X-irradiated sample at the orientation EC₃ during isochronal annealing revealed mutual transformations of F- and F⁺-centers within the dosimetric peak from 380 to 500 K. The transformations occurred simultaneously with emptying of the electron trap whose OA is at 2.8 eV. The predominant F→F⁺ conversion, which could be explained by delocalization of holes, was observed in the low-temperature part of the peak near 380–440 K. From the available experimental data it was inferred that the simultaneous release of electrons and holes in the low-temperature part of the peak facilitated formation of excitons bound on F-type centers. The excitons transferred part of the energy stored in the irradiated crystal to F⁺- and F⁻-centers during thermal stimulation, leading to luminescence of these centers.     

Photoluminescence and capacitance–voltage characterization of GaAs surface passivated by an ultrathin GaN interface control layer

A novel surface passivation technique for GaAs using an ultrathin GaN interface control layer (GaN ICL) formed by surface nitridation was characterized by ultrahigh vacuum (UHV) photoluminescence (PL) and capacitance–voltage (C–V) measurements. The PL quantum efficiency was dramatically enhanced after being passivated by the GaN ICL structure, reaching as high as 30 times of the initial clean GaAs surface. Further analysis of PL data was done by the PL surface state spectroscopy (PLS³) simulation technique. PL and C–V results are in good agreement indicating that ultrathin GaN ICL reduces the gap states and unpins the Fermi level, realizing a wide movement of Fermi level within the midgap region and reduction of the effective surface recombination velocity by a factor of 1/60. GaN layer also introduced a large negative surface fixed charge of about 10¹² cm⁻². A further improvement took place by depositing a Si₃N₄ layer on GaN ICL/GaAs structure.     

Structural and compositional analysis of InBixAsySb(1−x−y) films grown on GaAs(0 0 1) substrates by liquid phase epitaxy

The growth of epitaxial InBi_xAs_ySb_(1−x−y) layers on highly lattice mis-matched semi-insulating GaAs substrates has been successfully achieved via the traditional liquid phase epitaxy. Orientation and single crystalline nature of the film have been confirmed by X-ray diffraction. Scanning electron micrograph shows abrupt interface at micrometer resolution. Surface composition of Bi(x) and As(y) in the InBi_xAs_ySb_(1−x−y) film was measured using energy dispersive X-ray analysis and found to be 2.5 and 10.5 at.%, respectively, and was further confirmed with X-ray photoelectron spectroscopy. Variation of the composition with depth of the film was studied by removing the layers with low current (20 μA) Ar⁺ etching. It was observed that with successive Ar⁺ etching, In/Sb ratio remained the same, while the As/Sb and Bi/Sb ratios changed slightly with etching time. However after about 5 min etching the As/Sb and Bi/Sb ratios reached constant values. The room temperature band gap of InBi_0.025As_0.105Sb_0.870 was found to be in the range of 0.113–0.120 eV. The measured values of mobility and carrier density at room temperature are 3.1×10⁴ cm² V⁻¹ s⁻¹ and 8.07×10¹⁶ cm⁻³, respectively.     

Top-quark rare decay t→ch in R-parity-violating SUSY

The flavor-changing top-quark decay t→ch, where h is the lightest CP-even Higgs boson in the minimal supersymmetric standard model, is examined in the R-parity-violating supersymmetric model. Within the existing bounds on the relevant R-parity-violating couplings, the branching fraction for t→ch can be as large as about 10⁻⁵ in some part of the parameter space.     

Analytical result for dimensionally regularized massless master non-planar double box with one-leg off shell

The dimensionally regularized massless non-planar double box Feynman diagram with powers of propagators equal to one, one leg off the mass shell, i.e., with p₁²=q²≠0, and three legs on shell, p_i²=0, i=2,3,4, is analytically calculated for general values of q² and the Mandelstam variables s,t and u (not necessarily restricted by the physical condition s+t+u=q²). An explicit result is expressed through (generalized) polylogarithms, up to the fourth order, dependent on rational combinations of q²,s,t and u, and simple finite two- and three-fold Mellin–Barnes integrals of products of gamma functions which are easily numerically evaluated for arbitrary non-zero values of the arguments.     

Analysis of frequency-dependent series resistance and interface states of In/SiO2/p-Si (MIS) structures

In this work, the investigation of the interface state density and series resistance from capacitance–voltage (C–V) and conductance–voltage (G/ω−V) characteristics in In/SiO₂/p-Si metal–insulator–semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO₂ film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 Å. The forward and reverse bias C–V and G/ω−V characteristics of MIS structures have been studied at the frequency range 30 kHz–1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance (R_s) and interface state density (D_it) values. Both the series resistance R_s and density of interface states D_it are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of R_s–V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO₂/p-Si MIS structures. The interface state density value of In/SiO₂/p-Si MIS diode calculated at strong accumulation region is 1.11×10¹² eV⁻¹ cm⁻² at 1 MHz. It is found that the calculated value of D_it (≈10¹² eV⁻¹ cm⁻²) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation.     

Correlation between electrical, optical properties and Ag centers of ZnO:Ag thin films

ZnO:Ag films have been fabricated on a n-Si (1 1 1) substrate and then annealed in situ in an O₂ ambient, using Ag₂O as a silver dopant by pulsed laser deposition. Hall measurements reveal that the films prepared at 400 and 450 °C show p-type behavior with a hole concentration of 6.3×10¹⁶–1.2×10¹⁷ cm^–3 and a mobility of 2.48–3.30 cm²/V s. By combining Hall measurements, electron paramagnetic resonance (EPR) signals, and photoluminescence (PL) spectra, a correlation is observed between the free hole carriers, the Ag²⁺ centers, and the neutral acceptor bound excitons. Additionally, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I–V characteristic.     

Non-Fermi liquid regimes in U1−xMxPd2Al3(M=Y,Th)

The temperature-composition (T–x) phase diagram and NFL characteristics in the electrical resistivity ρ(T), specific heat C(T), and magnetic susceptibility χ(T) at low temperatures for the systems U_1−xM_xPd₂Al₃ (M=Y,Th) are described. The T–x phase diagram, the NFL characteristics, and the underlying mechanism for the NFL behavior are distinctly different for M=Y³⁺ and Th⁴⁺, apparently reflecting the difference in valence of the M atom substituents, and suggesting that U is tetravalent in these two systems.     

Trying to catch the elusive A and more. Reactions initiated by b-quarks and the Higgs sector of the MSSM

We study the cross sections for the production of neneural, intermediate mass Higgs boson in the process pp→ tq′φ, pp→tW⁻φ and pp→bZ⁰φ in the Minimal Supersymmetric Standard Model (φ = H⁰, h⁰ and A⁰) at Supercollider energies. The additional heavy particles (t, W, Z) in the final state can be used for tagging purposes, increasing the signal to background ratio. These reactions are dominated by bg and bg fusion. Their relevance for Higgs particle searches is discussed taking into account the expected efficiencies and purities for b-tagging. We find that, for tan β = 30, the cross sections for pp → bZ⁰φ are larger than 14 pb, over the whole intemediate range of M_A⁰, for A⁰ and at least one of the other two Higgses. Therefore this reaction is an excellent candidate for the discovery of one or more MSSM Higgs particles.     

The reactions pp→pΛK and pp→pΣK near their thresholds

The reactions pp→pΛK⁺ and pp→pΣ⁰K⁺ are studied near their thresholds. The strangeness production process is described by the π- and K exchange mechanisms. Effects from the final state interaction in the hyperon-nucleon system are taken into account rigorously. The Λ production turns out to be dominated by K exchange whereas K- as well as π exchange play an important role for the Σ⁰ case. It is shown that the experimentally observed strong suppression of Σ⁰ production compared to Λ production at the same excess energy can be explained by a destructive interference between π and K exchange in the reaction pp→pΣ⁰K⁺. Implications of such an interference on the reaction pp→nΣ⁺K⁺ are pointed out.     

EXAFS analysis of Er sites in Er–O and Er–F co-doped crystalline Si

We present extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) analyses of Er–O and Er–F co-doped Si. Samples were prepared by multiple implants at 77 K of Er and co-dopant (O or F) ions resulting in the formation of a2 μm thick amorphous layer uniformly doped with 1×10¹⁹ Er/cm³ and 3×10¹⁹ O/cm³, 1×10²⁰ O/cm³ or 1×10²⁰ F/cm³. EXAFS measurements show that the local environment of the Er sites in the amorphous layers consists of 6 Si first neighbors. After epitaxial regrowth at 620°C for 3 h, Er is fully coordinated with 8 F ions in the Er–F samples, while Si and O ions are concomitantly present in the first shell of O co-doped samples. Post regrowth thermal treatments at 900°C leave the coordination unchanged in the Er+F, while the Er+O (ratio 1 : 10) doped samples present Er sites with a fully O coordinated shell with an average of 5 O atoms and 4 O atoms after 30 s and 12 h, respectively. We have also found that the fine structure and intensity of the high-resolution PL spectra are strongly dependent on the Er-impurity ratio and on thermal process parameters in the Er–O co-doped samples, while this is not observed for the F-doped samples. The most intense PL response at 15 K was obtained for the 1 : 3 E : O ratio, suggesting that an incomplete O shell around Er is particularly suitable for optical excitation.     

Projective and affine connections on S and integrable systems

It is known that the Korteweg–de Vries (KdV) equation is a geodesic flow of an L² metric on the Bott–Virasoro group. This can also be interpreted as a flow on the space of projective connections on S¹. The space of differential operators Δ⁽ⁿ⁾=∂ⁿ+u₂∂ⁿ⁻²++u_n form the space of extended or generalized projective connections. If a projective connection is factorizable Δ⁽ⁿ⁾=(∂−((n+1)/2−1)p₁)(∂+(n−1)/2p_n) with respect to quasi primary fields p_i’s, then these fields satisfy ∑_i=1ⁿ((n+1)/2−i)p_i=0. In this paper we discuss the factorization of projective connection in terms of affine connections. It is shown that the Burgers equation and derivative non-linear Schrödinger (DNLS) equation or the Kaup–Newell equation is the Euler–Arnold flow on the space of affine connections.     

Pressure–temperature studies on conductivity of TlX(X=Cl,Br,I) compounds:: I: phase diagram. II: ionic mobility

We have measured the conductivity σ of TlX(X=Cl, Br, I) compounds up to 5.3 GPa and between 300–823 K. The σ–T dependence for all compounds can be divided into three distinct regions: (i) low temperature (LT), <400 K, with unusual negative σ–T dependence, (ii) intermediate temperature (IT), 400<650 K, with positive σ–T dependence and (iii) high temperature (HT), T>650 K, with positive σ–T dependence. The σ–T isobars were used to construct the T–P solid phase diagram for each compound. The LT region data indicate a new meta-stable phase in the 1.0–3.5 GPa range. The LT→IT transition is characterized by an inverse σ–T dependence followed by normal Arrhenius behavior up to and including the HT region. The extrapolation to 1 atm of the P-dependent boundary between IT and HT regions above 3 GPa for each compound in the P–T plot yields a value close to its respective normal (1 atm) T_melt suggesting a solid order–disorder transition type paralleling -AgI behavior. The abrupt drop in conductivity in the LT region for P between 2.5–4.1 GPa of all compounds is at variance with the Arrhenius behavior observed for unperturbed ion migration implying the appearance of a second factor overriding the Arrhenius temperature dependence. Normal Arrhenius σ–T dependence prevails in both IT and HT regions with Q_c values of 85–100 kJ mol⁻¹ and 50–75 kJ mol⁻¹, respectively. The higher conductivities at 0.4 GPa for TlBr and TlI relative to their 1 atm data and the increasing σ with P are in strong contrast to the normal σ-P behavior of TlCl. The dependence of activation volume ΔV^‡ on T for TlCl, i.e. ΔV^‡>0, shows abnormally high values with a maximum at 500 K for P<3.0 GPa but reasonable ΔV^‡ values appear above 3.0 GPa. The ΔV^‡–T dependence for both TlBr and TlI with ΔV^‡<0 is incompatible with an ion transport mechanism suggesting an electronic conduction process and implying an ionic–metallic transition at higher pressures. These contrasting conductivity features are discussed and interpreted in terms of electronegativity differences and bonding character rather than structure.     

钼酸铅晶体中F型色心电子结构的理论计算

运用相对论性的密度泛函离散变分(DV-Xα)方法模拟计算PbMoO₄晶体中可能存在的F型色心的电子结构.结果表明,F,F⁺心在PbMoO₄晶体的禁带中引入了施主能级,其光学跃迁能分别是2.141,2.186 eV,即F,F⁺心能分别引起PMO晶体中581,567 nm的吸收,该吸收与PbMoO₄晶体中580 nm的吸收峰对应.因此,可推断F型色心能引起PMO晶体中由光色效应引起的580 nm吸收.     

Nonergodicity and dynamical approach to the anharmonic oscillator

General lower bounds for the time average C^AA(∞)≡lim_T→∞(1/T)∝^T₀ C^AA(t) dt of the correlation C^AA(t)≡A(t)A(0)−A² of an arbitrary variable A are derived, which depend only on the temperature derivatives of the canonical averages of A and the Hamiltonian of the system. The bounds may be used to give good estimations for C^AA(∞) which is different from zero when A is nonergodic. It is important to take care of these terms when dynamical theories made for interacting systems are applied to isolated systems. We show explicitely that our recently developed dynamical approach to phonon systems with quartic anharmonicity yields excellent results for the corresponding isolated system, the anharmonic single well oscillator, when nonvanishing time averages are taken into account.     

DNA-based organic-on-inorganic semiconductor Schottky structures

A sandwich device has been fabricated from DNA molecular film by solution processing located between Al and p-type silicon inorganic semiconductor. We have performed the electrical characteristics of the device such as current–voltage (I–V), capacitance–voltage (C–V) and capacitance–frequency (C–f) at room temperature and in dark. The DNA-based structure has showed the rectifying behavior. From its optical absorbance spectrum, it has been seen that DNA has been a semiconductor-like material with wide optical band energy gap of 4.12 eV and resistivity of 1.6 × 10¹⁰ Ω cm representing a p-type conductivity.     

On the barrier inhomogeneities of polyaniline/p-Si/Al structure at low temperature

The current–voltage (I–V) characteristics of Au/polyaniline(PANI)/p-Si/Al structures were determined at various temperatures in the range of 90–300 K. The evaluation of the experimental I–V data reveals a decrease of the zero-bias barrier height (BH) and an increase of the ideality factor (n) with decreasing temperature. It was shown that the occurrence of a Gaussian distribution of then BHs is responsible for the decrease of the apparent BH, increase of the ideality factor n due to barrier height imhomogeneities that prevail at the interface. A Φ_b0 versus 1/T plot has been drawn for evidence of the Gaussian distribution of the barrier height, and and σ₀ = 0.0943 V for the mean barrier height and zero-bias standard deviation, respectively, have been obtained from this plot. Thus, a modified versus 1/T plot gives and A^* as 0.885 eV and A^* = 55.80 A/K² cm², respectively. Hence, it can be concluded that Au/PANI/p-Si/Al structure has a good rectifying contact and the temperature dependence of I–V characteristics of the rectifying contact on p-Si successfully have been explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.     

Effects of cation- or oxide ion-defect on conductivities of apatite-type La–Ge–O system ceramics

A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In La_xGe₆O_12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, La_x(GeO₄)₆O_1.5x−12 (x=8–9.33), and the highest conductivity was achieved for La₉(GeO₄)₆O_1.5 (x=9), where the number of cation (La³⁺) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La_9−0.66xSr_x(GeO₄)₆O_1.5 (x=0–1), La_9−1.33xZr_x(GeO₄)₆O_1.5 (x=0–1), La_9−xSr_x(GeO₄)₆O_1.5−0.5x (x=0–3), La_9−xZr_x(GeO₄)₆O_1.5+0.5x (x=0–1), La_x(GeO₄)_3x−21(AsO₄)_27−3xO_1.5 (x=0–3), La_x(GeO₄)_33−3x(AlO₄)_3x−27O_1.5 (x=0–3), La₉(GeO₄)_6−x (AlO₄)_xO_1.5−0.5x (x=0–3), La₉(GeO₄)_6−x(AsO₄)_xO_1.5+0.5x (x=0–1), La_9.33−xSr_x(GeO₄)₆O_2−0.5x (x=0–1.2) and La_x(GeO₄)_4.5(AlO₄)_1.5O_1.5x−12.75 (x=8.8–9.83), which were prepared by the partial substitution of La³⁺and GeO₄⁴⁻of the basic apatite La₉(GeO₄)₆O_1.5 with Sr²⁺ or Zr⁴⁺ and AlO₄⁵⁻ or AsO₄³⁻. Such substitutions lowered the conductivity of La₉(GeO₄)₆O_1.5. These results were discussed by the electrostatic interaction between Sr²⁺, Zr⁴⁺, AlO₄⁵⁻ or AsO₄³⁻ and oxide ion as a conductive species.