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1.
The polarization-modulated (PM) magnetoreflection technique has been used to study magnetic ordering effects in CdCr2S4 and EuSe. The energy gap for direct band-band transitions in CdCr2S4 has been measured to be EG = 2.3 eV, and the exchange splitting of the valence band to be about 0.03 eV. Good agreement with thin film absorption measurements is obtained in the temperature dependence of spectral structure, observed at energies less than EG, associated with crystal field and charge transfer transitions. No strongly blue-shifting peak is observed with magnetic order. PM magnetoreflection spectra of the E1 peak of EuSe show a direct manifestation of the spin alignment from the ferrimagnetic to ferromagnetic state of this crystal at 2 K in external fields up to 16 kOe. An attempt is made to explain resonant Raman scattering in EuSe (observed by other workers) in terms of the field-induced shift of one of the polarized E1 reflectivity components into coincidence with the 5145 Å argon-ion laser line. 相似文献
2.
We have observed the modulated reflectance spectra of n and p type GaSb at 300, 80, and 5 K from 0.56 to 2 eV. The modulated reflectance of intrinsic n type InSb was measured at 80 K from 0.2 to 2 eV. The “dry sandwich” vapor deposition technique was used to make the electroreflectance (ER) samples. The low-temperature spectrum of the undoped p type GaSb sample shows three peaks at the band edge that could be associated with transitions from the top of the valence band, the light (0.903 eV) and heavy (1.014eV) hole state Fermi levels to the conduction band. The energies of the observed peaks are in agreement with the Fermi level determination from Hall effect and Faraday rotation measurements. This modulation mechanism is based on band population effects. The ER signal of InSb under flatband condition at 80 K has five half oscillations at the direct band gap. The contribution of piezoelectric strain to ER is present since the dc bias required to achieve flatband condition is different at the band gap than at E1. The ER signal corresponding to the direct gap energy E0 and to the spin-orbit energy E0 + Δ0 was determined in the n and p type samples of GaSb at different temperatures. We have measured the intrinsic energy gap in GaSb at room temperature. Eg = 0.74 eV. The corresponding spin-orbit splitting was found to be Δ0 = 0.733 ± 0.002 eV. 相似文献
3.
We investigate the electronic structure of Ag2HgSnSe4 in a wurtzite-stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail. 相似文献
4.
D. Rönnow L.F. Lastras-Martínez M. Cardona 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):29-35
Within the past years the optical excitations of electrons have been measured for semiconductor samples of different isotope
compositions. The isotope shift observed have been compared with calculations of the effects of electron-phonon interaction
on the electronic band structure. While qualitative agreement has been obtained, some discrepancies remain especially concerning
the E1 and transitions. We have remeasured the effect of isotope mass on the E1 and transitions of germanium with several isotopic compositions. The results, obtained by means of spectroscopic ellipsometry,
confirm that the real part of the gap self-energies induced by electron-phonon interaction is larger than found from band
structure calculations, while the imaginary part agrees with those calculations, which are based on a pseudopotential band
structure and a bond charge model for the lattice dynamics. Our results agree with predictions based on the measured temperature
dependence of the gaps. We compare our data for E1 and with results for the lowest direct (E0) and indirect (Eg) gaps. The measured values of and increase noticeably with increasing isotope mass. Similar effects have been observed in the temperature dependence of in and . A microscopic explanation for this effect is not available.
Received: 6 March 1998 / Revised: 27 April 1998 /
Accepted: 15 May 1998 相似文献
5.
Barbara Sujak-Cyrul Bogumil Kolodka Jan Misiewicz Janusz M. Pawlikowski 《Journal of Physics and Chemistry of Solids》1982,43(11):1045-1051
Absorption measurements were made on single crystals and thin films of Zn3As2; within the photon energy range of 0.12–1.16 eV at temperatures of 300, 80 and 5 K and reflectivity was measured in the range of 1.0–5.5 eV at 300 K. Absorption below the fundamental edge has been interpreted as a process involving three mechanisms: (i) free-carrier absorption, (ii) intraband transitions between levels in the valence band, and (iii) direct transitions from valence levels to the acceptor level/band. The fundamental absorption edge has been ascribed to direct interband transitions from three valence levels to one conduction level. An isotropic three-level Kane band model has been used to interpret the experimental data, modified by introducing the light-hole level split from the heavy-hole level due to the tetragonal crystal field. A reasonable fit of the model to the experimental results has been obtained in the region of both intraband and interband absorption for the following set of parameters: Eg = 0.985 eV, ΔSO = 0.30 eV, ΔCF = 0.05 eV, m*hh = 0.36 m0 and P = 4 × 10?10eVm (at 300 K). A proposed Zn3As2 energy-band model near the Γ point is described to interpret the observed absorption. 相似文献
6.
We report here the study of the normal reflectivity spectra R and the corresponding derivative spectra (1/R) dR/dE of SbSI between 2 and 6 eV. The spectra show very strong anisotropy. We have also tried to use the change of the wavelength modulation spectrum to monitor the change in the band structure of SbSI due to the phase transition at 292 °C (D2h16→C2v9). Careful examination of the spectra at various temperatures around Tc shows no observable change. We report also the wavelength-modulated reflectivity spectra of the chalcopyrite crystal ZnGeP2 at 5 K between 2 and 6 eV, for E∥ C and E⊥ C. The experimental results are compared with the theoretical band structure calculation by de Alvarez and Cohen. We also present measurements on CsBr, CsI in the vacuum uv (between 5 and 8 eV) at 1.8K, showing noticeable difference with previous reflectivity measurements at 77 K. 相似文献
7.
J. Lange K. R. Baker J. H. Hamilton A. V. Ramayya L. Varnell J. J. Pinajian V. Maruhn-Rezwani 《Zeitschrift für Physik A Hadrons and Nuclei》1981,303(4):321-328
γγ-directional correlations have been measured between the ground state band transitions 6→4, 4→2 and 2→0 and the γ-rays depopulating the levels of the gamma vibrational band and the negative parity states of166Er. Thereby angular momenta could be assigned to the latter states andM2/E1 multipole mixtures determined for the depopulating γ-transitions. TheE2/M1 mixing ratios were obtained for a series ofI γ→I g transitions up toI γ=8+. These are used to investigate the angular momentum dependence of theE2/M1 admixtures. 相似文献
8.
Gallium antimonide crystals highly doped with Mn were prepared by a liquid-phase-electroepitaxy growth method. The crystals exhibited high hole concentrations up to 6×1018 cm−3. Photoluminescence (PL) and transmission techniques were used for their investigation. Spectral line-shapes typical for highly doped semiconductors were observed. The lines revealed the features corresponding to band gap narrowing and valence-band filling phenomena. Values of the band-gap narrowing ΔEg and the degree of the valence-band filling ΔEF were estimated from the PL spectra. The ionization energy of the Mn acceptor Ei was estimated to be approximately 15.1-15.6 meV. At low temperatures, the PL maxima shifted relatively strongly towards higher energy with temperature. The shifts most probably resulted from a dramatic change in the electron density of states near the bottom of the conduction band. The extent of low-energy tails of the PL bands correlates with the doping levels. The transmission spectra exhibited an absorption band centred at around 774-780 meV. The band most probably originated in electron transitions from the level of spin-orbit splitting to the top of the valence band. 相似文献
9.
Razika Brahimi Yassine Bessekhouad Mohamed Trari 《Physica B: Condensed Matter》2012,407(18):3897-3904
The compounds NxTiO2(x=0, 0.05, 0.1, 0.2) with the anatase structure have been synthesized by Sol–Gel method using Tri-ethyl Amine as nitrogen source and their optical, electrical and electrochemical properties are investigated. The electrical conductivity and thermoelectric power are measured in the temperature rang 300–600 K. The samples exhibit p-type behavior in contrast to TiO2. The doped-samples exhibit two optical transitions (2.35≤Eh−Vis(eV)≤2.55; 1.97≤El−Vis (eV)≤2.06) directly allowed in the visible region, while only one transition is observed in UV region (EUV∼3.00 eV). Pure TiO2 shows direct band gap transition of 3.17 eV. The results confirm experimentally the calculations of Di. Valentin et al. [42]. The transitions Eh−Vis and El−Vis are attributed respectively to the promotion of electrons from the localized N 2p and π? N–O bond to the conduction band. In all cases, EUV is associated to the forbidden band energy. Though that the conductivity is generally improved by doping process, only N0.05TiO2 and N0.1TiO2 shows an enhanced mobility. The mechanism of conduction takes place by small polaron hopping. The band edge positions of NxTiO2 (x=0, 0.05, 0.1, 0.2) at room temperature is predicted from the obtained physical properties. This study proves experimentally the principal role of nitrogen in doping process and permits the electronic states localization associated with N-impurities in TiO2 anatase. 相似文献
10.
K. Goksen 《Journal of Physics and Chemistry of Solids》2008,69(10):2385-2389
Transmission and reflection measurements in the wavelength region 450-1100 nm were carried out on Tl4In3GaS8-layered single crystals. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 2.32 and 2.52 eV, respectively. The rate of change of the indirect band gap with temperature dEgi/dT=-6.0×10−4 eV/K was determined from transmission measurements in the temperature range of 10-300 K. The absolute zero value of the band gap energy was obtained as Egi(0)=2.44 eV. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index were found to be 4.87 eV, 26.77 eV, 8.48×1013 m−2 and 2.55, respectively. 相似文献
11.
V. A. Pustovarov I. N. Ogorodnikov S. I. Omelkov L. I. Isaenko A. P. Yelisseyev A. A. Goloshumova S. I. Lobanov P. G. Krinitsyn 《Physics of the Solid State》2014,56(3):456-467
The electronic and crystal structures of SrMgF4 single crystals grown by the Bridgman method have been investigated. The undoped SrMgF4 single crystals have been studied using low-temperature (T = 10 K) time-resolved fluorescence optical and vacuum ultraviolet spectroscopy under selective excitation by synchrotron radiation (3.7–36.0 eV). Based on the measured reflectivity spectra and calculated spectra of the optical constants, the following parameters of the electronic structure have been determined for the first time: the minimum energy of interband transitions E g = 12.55 eV, the position of the first exciton peak E n = 1 = 11.37 eV, the position of the maximum of the “exciton” luminescence excitation band at 10.7 eV, and the position of the fundamental absorption edge at 10.3 eV. It has been found that photoluminescence excitation occurs predominantly in the region of the low-energy fundamental absorption edge of the crystal and that, at energies above E g , the energy transfer from the matrix to luminescence centers is inefficient. The exciton migration is the main excitation channel of photoluminescence bands at 2.6–3.3 and 3.3–4.2 eV. The direct photoexcitation is characteristic of photoluminescence from defects at 1.8–2.6 and 4.2–5.5 eV. 相似文献
12.
Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8-4.4 eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E0, E1A, and E1B interband transitions, have been determined using the simulated annealing algorithm. 相似文献
13.
H. Neumann B. Perlt N.A.K. Abdul-Hussein R.D. Tomlinson A.E. Hill 《Solid State Communications》1982,42(12):855-856
Optical absorption spectra of polycrystalline and amorphous CuInSe2 thin films were measured at room temperature in the photon energy range from 0.8 to 2.1 eV. In amorphous CuInSe2 the absorption coefficient follows the relation α(hv) = A(hv?E0)/hv characteristic of optical transitions between extended states in both the valence and conduction band. The optical gap of E0 = 1.38 ± 0.01 eV is larger than the fundamental gap energy of Eg = 1.01 ± 0.01 eV in crystalline CuInSe2. A comparison of the results for CuInSe2 with those for ZnSe is given. 相似文献
14.
The optical properties of the SrFX (X=Cl, Br, I) compound have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for band structure calculations. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε1(0). We find that the value of ε1(0) increases on decreasing the energy gap. The reflectivity spectra and absorption coefficient have been calculated and compared with the available experimental data. 相似文献
15.
利用室温下压电调制反射光(PzR)谱技术系统测量了N掺杂浓度为0.0%—3%的分子束外延生长GaNxAs1-x薄膜,并对图谱中所观察的光学跃迁进行了指认.在GaN0.005As0.995和GaN0.01As0.99薄膜的PzR谱中观察到此前只在椭圆偏振谱中才看到的N掺杂相关能态E1+Δ1+ΔN.当N掺杂浓度达到
关键词:
压电调制反射光谱(PzR)
xAs1-x薄膜')" href="#">GaNxAs1-x薄膜
分子束外延(MBE) 相似文献
16.
Dapeng Xu Yipeng Gu Liang Li Hongzhi Shen Hang Yang Qiang Zhou Zhan Shi Hongming Yuan Tian Cui 《Journal of Physics and Chemistry of Solids》2014
A high-quality ZnNb2O6 single-crystal grown by optical floating zone method has been used as a research prototype to analyze the optoelectronic parameters by measuring the absorption coefficient and transmittance spectra along the b-axis from 200 nm to 1000 nm at room temperature. The optical interband transitions of ZnNb2O6 have been determined as a direct transition with a band gap of 3.84 eV. The refractive index, extinction coefficient, and real and imaginary parts of the complex dielectric constants as functions of the wavelength for ZnNb2O6 crystal are obtained from the measured absorption coefficients and transmittance spectra. In the Urbach tail of 3.16–3.60 eV, the validity of the Cauchy–Sellmeier equation has also been evaluated. Using the single effective oscillator model, the oscillator energy Eo is found to be 4.77 eV. The dispersion energy Ed is 26.88 eV and ZnNb2O6 crystal takes an ionic value. 相似文献
17.
We have extended to higher N and to Ka = 3 and 4 the rotational analysis of the 7390-Å band of NO2 performed by K. E. Hallin and A. J. Merer (Canad. J. Phys.55, 2101–2112 (1977)). The lines belong to a perturbed parallel band for which Hallin and others have proposed the vibrational assignment (2 13 1)-(0 0 0) within the electronic ground state. These authors presumed that this band borrows its intensity through a vibronic coupling (spin-orbit and/or Coriolis coupling) from the stronger (0 2 0)-(0 0 0) band of the electronic system at 7460 Å. We have observed about 900 transitions belonging to the Ka = 0, 1, 2, 3, 4 subbands of the (2 13 1)-(0 0 0) band for N values going up to about 23, and 300 lines of the “hot” band (2 13 1)-(0 1 0). We have also looked for spin-orbit-induced transitions and we have detected about 400 transitions with ΔN ≠ ΔJ. Among them ΔN = ±2 transitions with ΔKa = 0 or ± 2 have been observed, indicating that N and Ka are no longer good quantum numbers, and demonstrating clearly the existence of rovibronic interactions perturbing the upper levels of the transitions. 相似文献
18.
Optical properties of Hg1 ? x ? y Cd x Eu y Se crystals grown by the Bridgman method have been investigated based on the independent reflectance and transmittance measurements, which were performed on a Nicolet 6700 spectrometer at T = 300 K in the wavelength range 0.9 ≤ λ ≤ 26.6 μm. The values of refractive index n, absorption index k, and absorption coefficient α have been determined for the crystals studied. Based on the dependences α = f(hν), the presence of direct allowed interband optical transitions in the crystals is established and the band-gap values are determined. The influence of temperature on the transmittance and band gap are investigated in the range T = 114–300 K. 相似文献
19.
The band structure of the CdxHg1?xTe mixed crystals have been computed on the basis of tight-binding interpolation scheme and virtual crystal approximation. The bowing parameters of main energy gaps have been calculated as well as composition dependence of position of E1 and E1 + Δ1 maxima in reflectivity spectra. Good agreement with previously reported experimental data has been found. 相似文献
20.
We report measurements of piezobirefringence in GaP and InP in the region below the direct gap. For GaP this includes the region above the indirect gap where the sample is opaque. The experimental data are compared with theoretical calculations of the contributions to the piezobirefringence arising from the E0, E1 and E2 transitions. 相似文献