X centers in ZnSe〈Ga〉 and ZnSe〈As〉 single crystals

The results of experimental studies of the energy spectrum of X centers in ZnSe〈Ga〉 and ZnSe〈As〉 single crystals are presented; the results are in accord with the available calculations. The Stokes shift, the stabilization of the Fermi level near the extrema of allowed bands of ZnSe, anomalies in thermoluminescence and interband photoluminescence, and some other effects are explained on the basis of configuration-coordinate diagrams for associated defects V_Zn-Ga_i and V_Se-As_i, taking into account tetrahedral and hexagonal positions of interstitial atoms. The absence of residual photoconductivity is attributed to the presence of r-and s-recombination centers in the crystals.     

Electron tunneling effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells

We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells.It is shown that only the doped sample shows electron cyclotron-resonance absorption.Also,the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra,and the doped one shows only one peak.The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other.The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field,and can cancel out a built-in electric field as observed in the undoped structures.     

Cathodoluminescence of ZnSe(Bi):Al crystals

The cathodoluminescence (CL) in ZnSe crystals annealed at T=1200 K in a Bi melt containing an aluminum impurity is investigated. The spectra are recorded for different excitation levels, temperatures, and detection delay times t ₀. As t ₀ is increased, the intensity of the orange band at λ _max=630 nm (1.968 eV) in the CL spectrum decreases in comparison to the intensity of the dominant yellow-green band at λ _max=550 nm (2.254 eV), whose half-width increases in the temperature range 6–120 K and then decreases as the temperature increases further. It is shown that such behavior of the yellow-green band is caused by the competition between two processes: recombination of donor-acceptor pairs and of free electrons with holes trapped on acceptors. The former mechanism is dominant at low temperatures, and the latter mechanism is dominant at high temperatures. At T∼120 mK the contributions of the two mechanisms to the luminescence are comparable. The resultant structureless band then achieves its greatest half-width, which is dictated by the interaction of the recombining charge carriers with longitudinal-optical and longitudinal-acoustic phonons and with the free-electron plasma. The mean number of longitudinal-optical phonons emitted per photon is determined mainly by their interaction with holes trapped on deep acceptors in the form of Al atoms replacing Se. The donor in the pair under consideration is an interstitial Al atom. Fiz. Tverd. Tela (St. Petersburg) 39, 1526–1531 (September 1997)     

Fe~(16+)(1s~22s~22p~6)辐射复合截面的相对论理论研究

利用Dirac-Slater相对论平均自洽场理论,研究了类氖铁离子Fe16+(1s22s22p6)与自由电子的辐射复合(RR)截面,在分析相对论量子数的取值范围及原子模型等对n壳层RR截面的影响的基础上,给出了n壳层RR截面随自由电子能量变化的一般规律.     

The influence of light intensity on surface recombination in GaS single crystals

Gallium sulphide (GaS) is a layer structure semiconductor with relatively wide energy gap (E_g (295 K) = 2.5 eV and E_g (80 K) = 2.62 eV). It has potential applications in some areas of optoelectronics. This paper presents the investigations of the influence of light intensity on surface recombination velocity of charge carriers in GaS single crystals. To attain this purpose spectral dependences (between 420 and 550 nm) of absorption coefficients, reflectivity coefficients and photoconductivity were measured in vacuum. The investigations were performed for various light intensities in several temperatures from 80 to 333 K. The least square method was applied to fit the theoretical dependences of photoconductivity on wavelength and intensity of illumination at these temperatures. From the fittings the temperature and light intensity dependences of surface recombination velocity and bulk lifetime of charge carriers were obtained.     

原子实对离子n壳层辐射复合截面的影响

基于Dirac-Slater相对论平均自洽场理论和类氢模型,研究了自由电子被辐射复合到裸核和类裸核离子的n壳层时RR截面随自由电子能量的变化,以及原子实对这种变化的影响;给出了两种理论模型下RR截面曲线变化的差异,并对这种差异做了较详细的理论说明.     

Atomic and electron structure of reconstructed (111) surface in ZnSe and CdSe crystals

The atomic and electron structure of four variants of polar (111)-(2 × 2) surfaces in ZnSe and CdSe terminated by a cation, namely, the ideal, relaxed, reconstructed, and relaxed after reconstruction surfaces, are calculated for the first time from the first principles. The surface is simulated by a film with a thickness of 12 atomic layers and a vacuum gap of ~16 Å in the layered superlattice approximation. Four fictitious hydrogen atoms with a charge of 0.5 electrons each are added for closing dangling Se bonds on the opposite side of the film. Ab initio calculations are performed using the QUANTUM ESPRESSO software based on the density functional theory. It is shown that relaxation results in splitting of atomic layers. We calculate and analyze the band structures and total and layer-wise densities of electron states for four variants of the surface.

     

Search for X(3872) in gammagamma fusion and radiative production at CLEO

We report on a search for the recently reported X(3872) state using 15.1 fb(-1) of e(+)e(-) data taken in the sqrt[s] = 9.46-11.30 GeV region. Separate searches for the production of the X(3872) in untagged gammagamma fusion and e(+)e(-) annihilation following initial state radiation are made by taking advantage of the unique angular correlation between the leptons from the decay J/psi --> l(+)l(-) in X(3872) decay to pi(+)pi(-)J/psi. No signals are observed in either case, and 90% confidence upper limits are established as (2J+1)Gamma(gammagamma)(X(3872))B(X --> pi(+)pi(-)J/psi) < 12.9 eV and Gamma(ee)(X(3872))B(X- -> pi(+)pi(-)J/psi) < 8.3 eV.     

Effect of non-equilibrium acoustic phonons on radiative recombination in semiconductors

We report the first direct observation of radiative no-phonon and acoustic phonon-assisted transitions, determination of relative rates of radiative and non-radiative phonon-assisted decay for centres of various types in semiconductors. We also have suggested improvement of experimental approach to get a form of the distribution function for non-equilibrium acoustic phonons in crystals.     

Temperature dependence of the radiative recombination coefficient in GaAs---(Al, Ga)As quantum wells

The temperature dependence of the radiative recombination coefficient of GaAs---(Al,Ga)As quantum wells grown by MO-VPE was investigated. This was done by measuring the minority carrier lifetime as deduced from photoluminescence decay. The experimental lifetime varies as T^a, where a equals 1.1 for small well thicknesses (66Å) and increases gradually to 1.4 for a well thickness of 300Å. This is in good agreement with simple theoretical considerations.     

PrP_5O_(14)晶体中Pr~(3+)离子的f-d辐射跃迁

本文讨论了计算稀土离子4f~(N-1)5d-f~N辐射跃迁几率的一般方法,提出了这类跃迁的亲态选择定则。并在C_(2v)群对称下,具体计算了Pr~(3+)离子在PrP_5O_(14)晶体中的f-d辐射跃迁几率,结果指出稀土离子的f-d跃迁几率比f-f跃迁几率大得多。     

Thermal stability of Li-related 1D defects in ZnSe:Li/GaAs grown by MBE

Curved streak patterns are clearly observed in the azimuth of [1 0 0] when the substrate temperature is heated up to 600°C, suggesting that the one-dimensional Li chains are stable. The growth rates of non-doped ZnSe on Li-doped ZnSe are found to be about 1/2 of that of non-doped ZnSe grown on GaAs. Even when no Li is supplied, the RHEED exhibits clear curved streak patterns. The results indicate that Li atoms segregate onto the topmost surface during the MBE growth, because of high diffusivity of Li, resulting in the formation of 1D array.     

Short-living defects and recombination processes in Li6Gd(BO3)3 crystals

Results of a study of transient optical absorption (TOA) and luminescence of lithium-gadolinium orthoborate Li₆Gd(BO₃)₃ (LGBO) in the visible and ultraviolet spectral regions are presented. As revealed by absorption optical spectroscopy with nanosecond time resolution, the LGBO TOA derives from optical transitions in hole centers, with the optical density relaxation kinetics being mediated by interdefect tunneling recombination involving these centers and neutral lithium atoms acting as electronic Li⁰ centers. At 290 K, the Li⁰ centers are involved in thermally stimulated migration, which is not accompanied by carrier transfer to the conduction or valence band. The slow TOA decay kinetics components, with characteristic times ranging from a few milliseconds to seconds, have been assigned to diffusion-limited annihilation of lithium interstitials with vacancies. The mechanisms responsible for the creation and relaxation of short-living Frenkel defect pairs in the LGBO cation sublattice have been analyzed.     

The radiative decay of $ \psi$(3770) into the predicted scalar state X(3700)

We calculate the radiative decay width of the (3770) into the dynamically generated scalar resonance X(3700) which is predicted in a previous paper. The results show that it is possible that the upgraded BEPC-II facility will generate enough statistics in order to observe this decay and thus confirm the existence of the X(3700) .     

Effect of composition fluctuations on radiative recombination in narrow-gap semiconductor solid solutions

The photoluminescence of the epitaxial structures based on the narrow-gap CdHgTe solid solutions has been experimentally investigated and the presence of large-scale composition fluctuations localizing carriers in the structures has been established. A model has been proposed for describing the effect of the fluctuations on the radiative recombination rate, the shape of the luminescence spectra, and their peak position. The model describes carrier transport and recombination at the strongly inhomogeneous composition of the solid solution and demonstrates the manifestation of carrier localization in the luminescence spectra.