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1.
Using the first-principles methods we compute the electronic structure and the absorption spectra for a wurtzite CdSe (0001) slab covered with zincblende ZnSe and ZnS epilayers. For each structure we compute the DOS and the imaginary part of the dielectric function. We find that the semiconductor passivation shifts the ‘near Fermi-level’ states of the bare CdSe slab down to lower energy levels. The migration suggests the decrease of surface effects and energy loss. We observe the substantial reduction of the abnormal peaks in the absorption spectra of the bare CdSe slab, which seems to be a consequence of the DOS migration. This is consistent with the experimental results that a proper passivation enhance the luminescence efficiency. We also study the case that the epilayer surface is terminated with PH3 and find the PH3 passivation also reduces the surface state to some extent. 相似文献
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Z. Mierczyk A. Majchrowski K. O
ga A. Slezak I.V. Kityk 《Optics & Laser Technology》2006,38(7):558-564
The paper presents theoretical approach to simulation of nonlinear optical absorption in zinc selenide crystals doped with cobalt (II) ions (ZnSe:Co2+), which was reported by us earlier (Opt. Laser Technology, V. 35, (2003), 169). We used ZnSe:Co2+ crystals as saturable absorbers for generation of giant-pulse eye-safe laser radiation. It was found that minimal optical losses (maximal final transmission) occurred for ZnSe samples containing 1.6×1019 cm−3 of Co2+ ions. Band structure and photoinduced molecular dynamics simulations were performed to explain the parabolic dependence of optical losses versus Co2+ concentration. The minimum was shown to be the result of photoinduced anharmonic electron–phonon interaction. 相似文献
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Dietmar Theis 《Journal of Physics and Chemistry of Solids》1977,38(10):1125-1129
Wavelength modulated reflection spectrometry is used to obtain the temperature coefficients for the fundamental and higher transitions in ZnSe and ZnS up to 8 eV. The experimentally obtained values are compared to results of a Brooks-Yu type calculation. Agreement is satisfactory for higher transitions. The temperature shift of the spectral site of the fundamental exciton is explained in terms of the influence of phonon generated microfields. 相似文献
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The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs. 相似文献
5.
The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs. 相似文献
6.
NoSoung Myoung Vladimir V. Fedorov Sergey B. Mirov Lowell E. Wenger 《Journal of luminescence》2012,132(3):600-606
Concentration dependences of the mid-IR kinetic of luminescence at 5E?5T2 transition in Fe:ZnSe and Fe:ZnS laser samples were studied in 14–300 K temperature ranges. Radiation lifetime in Fe:ZnSe samples measured using low doped samples with iron concentration 0.1×1018 cm?3 was estimated to be 57 μs. The magnetic susceptibility for higher doped (CFe=38 and 112×1018 cm?3) Fe:ZnSe samples was found to consist of a paramagnetic Curie–Weiss behavior arising from the weakly interacting Fe2+ ions and a diamagnetic ZnSe contribution plus a temperature-independent, field-dependent contribution possibly arising from very small amounts of aggregated Fe. 相似文献
7.
《Surface science》1987,188(3):L708-L716
8.
The complete set of non-vanishing third-order elastic constants of the semiconductors ZnS and ZnSe is obtained theoretically. The strain energy density is estimated using finite strain elasticity theory by considering the interactions up to two nearest neighbours of each atom in the unit cell of these compounds. This energy density is compared with the strain dependent lattice energy density from the continuum model approximation. The second-order parameter of the potential function φ is obtained from the measured principal axis Cij. The third-order potential parameter is estimated by assuming a Lennard-Jones type of interatomic potential. The interlattice displacements as well as the second-order elastic constants are evaluated along with the six third-order elastic constants of ZnS and ZnSe. Using these second- and third-order elastic constants of ZnS, the pressure derivatives of second-order elastic constants are evaluated. The second- and third-order elastic constants of ZnSe are compared with the available experimental values. The third-order elastic constants show anisotropy in different directions. 相似文献
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运用密度泛函理论体系下的平面波赝势(PWP)和广义梯度近似(GGA)方法,计算研究了闪锌矿结构的ZnS晶体在不同的外界压强下的电子结构. 通过分析发现,随着外界压强的增大,晶格常数和键长在不断缩小,从S原子向Zn原子转移的电荷越来越少,Zn—S键的共价性逐渐增强,Zn原子和S原子的态密度都有不同程度的变化,而且还有向低能量移动的趋势. 当外界压强达到24GPA时,ZnS从直接带隙半导体变成间接带隙半导体,而且随着压强的增大,间接带隙逐渐变小,直接带隙逐渐增大.
关键词:
闪锌矿结构
态密度
能带结构
密度泛函理论 相似文献
12.
Band structure of lithium, sodium, and potassium nitrites, nitrates, chlorates, perchlorates, sulfites, and sulfates together
with the state density and the imaginary part of the complex dielectric permittivity is calculated by the DFT-LDA method with
the Perdew and Zunger (PZ) correlation potential using the software package CRYSTAL06 on the uniform grid comprising 512 points
of the Brillouin zone in the approximation of the direct interband transitions and constant matrix element. Good agreement
of experimental and theoretical optical spectra is established. It is demonstrated that the main specific features of the
optical spectra at energies of 5–12 eV are determined by the complex anion structure and depend only slightly on the cation
structure. The cation excitation energies are 25‒28 eV for sodium salts and 15‒18 eV for potassium ones. 相似文献
13.
The influence of sodium impurity on photoluminescence (PL) spectra of ZnSe crystals doped in a growth process from a Se+Na melt is investigated. It is shown that the introduction of the impurity results in emergence of emission bands in the PL spectra due to the recombination of exciton impurity complexes associated with both donors and hydrogen-like acceptors. Apart from that, four bands generated by donor-acceptor pairs recombination and a band produced by electronic transitions from the conduction band to a shallow acceptor are discussed. As a result of the analysis it is concluded that Na impurity forms in ZnSe lattice NaZn hydrogen-like acceptors with activation energy of 105±3 meV, Nai donor centers with activation energy of 18±3 meV, as well as NaZnVSe and NaiNaZn associative donors with activation energy of 35±3 and 52±9 meV, respectively. 相似文献
14.
P. N. Krylov E. A. Romanov I. V. Fedotova 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2013,7(3):458-462
The influence of the condensation temperature on the structure and optical properties of ZnS and ZnSe films is studied. The presence of the hexagonal phase, along with the cubic, is revealed in films deposited on the cleaved NaCl facet. The appearance of the hexagonal phase is explained by the mechanical stress produced at the film-substrate interface. 相似文献
15.
Ya. O. Dovgii I. V. Kityk S. N. Pidzyrailo Z. A. Khapko 《Journal of Applied Spectroscopy》1990,53(6):1319-1322
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 6, pp. 988–991, December, 1990. 相似文献
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V. I. Kovalev P. I. Kuznetsov V. A. Zhitov L. Yu. Zakharov A. I. Rukovishnikov A. V. Khomich G. G. Yakushcheva S. V. Gaponenko 《Journal of Applied Spectroscopy》2002,69(2):298-304
By the method of spectral ellipsometry with binary modulation of the polarization state the dispersions of the refractive index n, absorption coefficient k, and layer thickness in ZnS/ZnSe multilayer structures grown by the chemical gasphase deposition method from heteroorganic compounds on GaGaAssubstrates with ZnSe buffer layers have been determined. The efficiency of local ellipsometric measurements (with a light beam size less than 150 × 500 m) permitting mapping of the parameters of structures with A2B6 layers up to a few microns thick has been demonstrated. The optical properties of oxide layers formed on the zinc selenide surface have been investigated. Multilayer structures (ZnSe/ZnS)
n
/ZnSe/GaAs with a pronounced exciton absorption and specific features in the reflection spectra coinciding in energy with exciton transitions, as well as Bragg mirrors with a reflection coefficient up to 99% in the blue region of the spectrum, have been studied. 相似文献
19.
In order to elucidate the nature of the red emission band at 660 nm in ZnS: Fe crystals, the equilibrium luminescence, the thermoluminescence and the photoinduced EPR signals were measured, using UV, or the simultaneous UV + IR excitations. In addition, the polarization properties and the light-pressure shift of the red luminescence were studied. On the basis of the obtained results and of the data reported in the literature and concerning the red and IR emissions in ZnS: Fe a donor-acceptor model is proposed, in which the transition Cl2?→Fe3+ would give rise to the 660 nm band. 相似文献
20.
基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,对闪锌矿结构(ZB)和岩盐结构(RS)的ZnSe在0—20GPa高压下的几何结构、态密度、能带结构进行了计算研究,分析了闪锌矿结构ZnSe和岩盐结构ZnSe的几何结构.在此基础上,研究了ZnSe的结构相变、弹性常数、成键情况以及相变压强下电子结构的变化机理.结果发现:通过焓相等原理得到的ZB相到RS相的相变压强为15.3GPa,而由弹性常数判据得到的相变压强为11.52GPa,但在9.5GPa左右并没有发现简单立方相的出现;在结构相变过程中,sp3轨道杂化现象并未消除,Zn原子的4s电子在RS相ZnSe的导电性中起主要贡献. 相似文献