Silicon doping of MBE-grown GaAs films

Two concentration ranges of silicon doping in MBE-grown GaAs films have been investigated in some detail. In lightly doped films, with a free-electron concentration of ≈10¹⁶cm^?3, low-temperature photoluminescence spectra have been analysed to develop a model to account for spectral features previously attributed to Ge and Si acceptor levels. In heavily doped films, a maximum free-electron concentration of ≈7×10¹⁸ cm^?3 has been obtained, which is only rather weakly dependent on growth conditions and the nature of the arsenic species (As₂ or As₄). Transmission electron microscopy has shown that no significant precipitation effects occur when higher Si fluxes are used but there is evidence for autocompensation. The maximum PL intensity (300 K) is found at a lower free electron concentration then with Sn-doped films, and is more sharply peaked, but there is no evidence for an anomalous Moss-Burstein shift.     

Two-phonon Raman scattering in GaAs

The second-order Raman Spectrum of GaAs has been measured at room temperature by using an argon ion laser with Brewster's angle configuration. A number of critical points have been interpreted by considering neutron inelastic scattering work and detailed critical-point analysis in Ge. The Γ₁ component is the strongest in the spectrum where overtone scattering is dominant. Combination scattering has been observed in the energy region between 300 and 350 cm^?1for both Γ₁ and Γ₁₅ components. The second-order Raman spectrum is compared with the two-phonon overtone Raman intensity, calculated from neutron diffraction data. In the low frequency region, the Raman spectrum shows directly the one-phonon density of states of the TA phonon.     

Absorption coefficient of infrared laser window materials

The absorption coefficient of a number of potential i.r. laser window materials has been measured in the region of multiphonon absorption. Absorptions as low as 0·004 cm^?1 have been detected by using thick samples and a differential technique with a dual-beam spectrophotometer. The absorption coefficients of LiF, CaF₂, BaF₂, SrF₂, MgF₂, Al₂O₃, KCl, NaCl and KBr all decrease exponentially with increasing wavenumber. The slope of the exponential bears a nearly constant relationship to the longitudinal optical phonon frequency, consistent with a multiphonon process whose strength depends on the number of phonons generated. Absorption data are also presented for Si, Ge, GaAs: Cr, GaAs: Fe, ZnSe and CdTe.     

Structural investigation of Te-based chalcogenide glasses using Raman spectroscopy

Structural changes of metals (Zn, Sb, In, Ga) and metal halides (AgI, ZnI₂, CdI₂, PbI₂, BiI₃) modified GeTe₄ glasses were investigated with the aid of Raman spectroscopy. The Raman spectra of these glasses in the frequency region between 100 cm^?1 and 300 cm^?1 display four main bands at about 124, 140, 159 and 275 cm^?1 which are contributed by Ge–Te, Te–Te, Te–Te and Ge–Ge vibration modes. The intensity of 159 cm^?1 and 275 cm^?1 bands vary with the addition of different glass modifiers. While the relative intensity of the 124 cm^?1 and 140 cm^?1 bands are insensitive to composition changes. Glass modifiers like Zn, In and Sb act as glass network unstabilizer which will disorganize the glass network by opening up the chain structures of Ge–Te and Te–Te. In the case of Ga and metal halides, Ga can open up Ge–(Te–Te)_4/2 tetrahedra and form Ga–(Te–Te)_3/2 triangle. Iodine can form covalent bonds with tellurium and decrease the tendency of microcrystal formation. Thus both Ga and iodine ultimately act as glass network stabilizer.     

Infrared dielectric dispersion of ZnGeP2 and CdGeP2

The polarised i.r. reflectivity spectra of single crystals of the non-linear chalcopyrite materials ZnGeP₂ and CdGeP₂ have been measured over the spectral range 40–700 cm^?1. Analysis of the spectra using classical dispersion theory and the Kramers-Krönig technique has yielded, in each material, five modes with frequencies between 80 and 385 cm^?1 with the polarisation perpendicular to the optic axis. Parallel to the optic axis, two modes have been observed with frequencies between 300 and 400 cm^?1. The phonon dispersion curves of the isoelectronic analogue GaP have been used, together with a group theoretical analysis, to assign specific atomic displacements to the observed modes.     

The optical conductivity of free carriers in GaAs

The optical conductivity of free electrons in polar semiconducting compounds has recently been calculated by use of a generalized Boltzmann equation derived from the equation of motion of the quantum density matrix. This reduces to the quasi-classical Boltzmann transport equation in the low frequency limit: the optical conductivity thus obtained spans a spectral range from around 30cm^?1 to 1.2 × 10⁴cm^?1 in GaAs. In this paper, the optical conductivity is calculated for GaAs as a function of carrier concentration in terms of a frequency dependent relaxation time which reduces to the usual relaxation time in the limit of low frequencies and an elastic scattering mechanism. The low frequency limit of the relaxation time is used to estimate the mobility as a function of carrier concentration. The frequency dependent relaxation time is given for GaAs at 298 K over the spectral region from 45 cm^?1 to 2.3 × 10³cm^?1 for carrier concentrations from 3.4 × 10¹⁵cm^?3 to 8.7 × 10¹⁸cm^?3.     

Raman-brillouin light scattering determination of the structural correlation range in ges2 glass

Polarized Brillouin and low frequency (3 cm^?1 ? ω ? 40 cm^?1) Raman spectra of GeS₂ glass have been measured. Parameters determined from the Brillouin spectra have been used in the theory of Martin and Brenig to obtain from a fit of the Raman spectrum the structural correlation range, 2σ. We find 2σ = 8 ± 1 Å.     

Chemical characterization by XPS of Cu/Ge ohmic contacts to n-GaAs

Chemical composition of Cu/Ge layers deposited on a 1 μm thick n-type GaAs epitaxial layer (doped with Te to a concentration of 5 × 10¹⁸ cm⁻³) and its interface were examined ex situ by XPS combined with Ar⁺ sputtering. These measurements indicate a diffusion of Cu and Ge from the Cu/Ge layer towards GaAs and, also, an out-diffusion of Ga and As from the GaAs layer to the metallic films. The Auger parameter corrected Auger spectra and XPS spectra show only Cu and Ge metals in the in the Cu/Ge layer and in the interface.     

The ground-state rotational constants of germane

The ground-state rotational constants B₀, D₀, and H₀ have been determined for GeH₄ from the analysis of ground-state combination differences in the infrared spectra of isotopically enriched ⁷⁰GeH₄, ⁷²GeH₄, and ⁷⁴GeH₄. The spectra were recorded at 0.06-cm^?1 resolution and about 0.005-cm^?1 precision for unblended lines. Suitable combination differences were found in both the ν₂ and the ν₄ infrared bands. The ground-state constants were assumed to be invariant to isotopic substitution at Ge, and the tensor distortion constants were held fixed at their microwave values. The results obtained are: B₀ = 2.69587 ± 0.00007 cm^?1, D₀ = (3.34 ± 0.03) × 10^?5 cm^?1, H₀ = (1.3 ± 0.5) × 10^?9 cm^?1.     

High resolution diode laser measurements on the ν2 bands of 14NH3 and 15NH31

More than 500 lines in the ν₂ bands of ¹⁴NH₃ and ¹⁵NH₃ have been measured in the region 740–1200 cm^?1 with a diode laser spectrometer, with an accuracy better than 0.0005 cm^?1 for most of the lines. Wavenumbers (in cm^?1) were determined using a 3-in. Ge etalon for calibration and OCS, N₂O, NH₃, and CO₂ lines as references. The diode laser data were combined with pure inversion and inversion rotation frequencies and sets of rotational constants were obtained by the method of merged least squares. Perturbations between the Δk = ±3 levels have been taken into account in these calculations.     

Synthesis of Ge-Sn at high pressure and high temperature in a laser-heated diamond anvil cell

Ge–Sn compound is predicted to be a direct band gap semiconductor with a tunable band gap. However, the bulk synthesis of this material by conventional methods at ambient pressure is unsuccessful due to the poor solubility of Sn in Ge. We report the successful synthesis of Ge–Sn in a laser-heated diamond anvil cell (LHDAC) at ~7.6 GPa &; ~2000 K. In situ Raman spectroscopy of the sample showed, apart from the characteristic Raman modes of Ge TO (Г) and β-Sn TO (Г), two additional Raman modes at ~225 cm^?1 (named Ge–Sn₁) and ~133 cm^?1 (named Ge–Sn₂). When the sample was quenched, the Ge–Sn₁ mode remained stable at ~215 cm^?1, whereas the Ge–Sn₂ mode had diminished in intensity. Comparing the Ge–Sn Raman mode at ~225 cm^?1 with the one observed in thin film studies, we interpret that the observed phonon mode may be formed due to Sn-rich Ge–Sn system. The additional Raman mode seen at ~133 cm^?1 suggested the formation of low symmetry phase under high P–T conditions. The results are compared with Ge–Si binary system.     

Study of the ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by raman spectra

We have studied ion mobility in a Li_0.03Na_0.97Ta_0.4Nb_0.6O₃ solid solution by its Raman spectra. It has been revealed that, as the temperature of the solution is increased to approach the point of the phase transition to a state with a high conductivity with respect to lithium, the lines with frequencies at 77, 118, and 142 cm^?1, which refer, respectively, to librations of oxygen octahedra Nb(Ta)O6 as a whole and vibrations of Li and Na ions in octahedra, considerably broaden, decrease in intensity, and smear into the wing of the Rayleigh line. Remaining lines are preserved in the spectrum. We have observed that the width of the line with a frequency of 118 cm^?1 depends exponentially on temperature, while the width of the line with a frequency of 142 cm^?1 changes linearly with it, which makes it possible to attribute to the line with the frequency of 118 cm^?1 to vibrations of Li⁺ cations, whereas the line with the frequency of 142 cm^?1 should be attributed to vibrations of Na⁺ cations in AO₁₂ cuboctahedra. The average lifetime of Li⁺ ions in equilibrium positions and the jump barrier have been estimated to be ～8 × 10^?12 s and ～20 kJ/mol, respectively. This agrees well with the data in the literature on measurements of electric conductivity.     

Comparison of band model and integrated line-by-line synthetic spectra for methane in the 2.3 μm region

The 2.3 μm spectral region of methane can be used to retrieve cloud properties of planetary spectra, provided parameters for the methane spectrum are known. Two standard techniques for calculating absorption spectra in this region are compared here. A Voigt profile Mayer-Goody random band model is applied, using coefficients empirically fitted by Fink et al. to CH₄ spectra recorded with high absorping amounts at 10 cm^?1 resolution. Calculation of the absorption is also done with a line-by-line direct integration method for the same gas conditions using molecular parameters obtained by combining an older unpublished list of observed positions and estimated line strengths (derived from 0.04 cm^?1 resolution data) with quantum assignments from the literature. The molecular parameters have been evaluated for the 4180–4590 cm^?1 region by comparing new laboratory spectra with 0.01 cm^?1 resolution recorded at 296 and 153K with synthetic spectra calculated at the same conditions. The deficiencies of the molecular parameters and random band coefficients for this spectral region of CH₄ are then discussed qualitatively and demonstrated by comparing 10 cm^?1 resolution synthetic spectra calculated by both methods for the same gas conditions at 296, 153, and 55 K.Curves of growth of the total equivalent width are calculated at 296 and 55K for a pathlength of 50 cm and pressures up to 10 atm. Changing the mean line spacing in the band model gives better agreement between the spectra calculated by the two techniques at low gas temperatures. The required multiplier has been determined for the mean line spacing for pressures from 10^?6 to 10^?1 atm at 55, 100, and 150 K.     

Matrix isolation studies and potential function for perfluorocyclobutane

The infrared and Raman spectra of perfluorocyclobutane isolated in argon matrices at 1:100 and 1:200 mole ratios have been measured between 200 and 2000 cm^?1. Although the ring-puckering fundamental (ν₁₆) was not observed directly, an assignment for the 2 ← 1 (30 cm^?1) transition of ν₁₆ has been deduced from sum and difference bands resolved in the infrared spectrum. Potential functions based upon valence force models are considered in detail and correlated with those of similar ring systems. By using the frequency of the 2 ← 1 transition for ν₁₆ and a vibrational reduced mass of 1501 amu, an approximate model potential function calculation yields a slightly puckered equilibrium conformation with a barrier on the order of 124 cm^?1. The vibrational assignment for perfluorocyclobutane is discussed in terms of the new matrix isolation spectra.     

Measurement and analysis of the ν2 band of D216O

The rotational structure of the ν₂ band of D₂¹⁶O between 700 and 1550 cm^?1 has been analyzed from spectra recorded with a Fourier transform spectrometer (nominal resolution: 0.1 cm^?1). By applying Watson's reduced Hamiltonian and a least squares method to the set of observed transitions, together with microwave data and the infrared data of Williamson, 22 rotational constants for the ground state and 17 for the upper state have been obtained which predict the positions of more than 700 observed lines with a standard deviation of 0.04 cm^?1.     

Raman study of InAs/GaAs quantum dot solar cells

We report polarized and resonant Raman study of InAs/GaAs quantum dot solar cell (QDSC) structures. Raman spectra obtained from the top surfaces of the samples suggested that the formation of InAs QDs induced tensile strain in the overgrown GaAs layers. Furthermore, a longitudinal optical phonon-plasmon (LPP) coupled modes were observed in the p-type GaAs layers. The tensile strain was increased with an increase in the QD size. The hole concentrations estimated by fitting the individual LPP coupled modes were in the range of 2.4–3.5 × 10¹⁸ cm^?3. Resonant Raman spectra obtained from the cleaved sides, where the QDs were located, showed a 225 cm^?1 mode in parallel polarization configurations. Based on accurate analysis, this mode was identified as the LA(X) phonon of GaAs.     

高组份Al值的AlxGa1-x As和AlxGa1-x As/GaAs/AlxGa1-xAs/GaAs多层结构的MOCVD生长

用自制常压MOCVD系统,在半绝缘GaAs衬底上生长高Al组份Al_xGa_1-xAs（其x值达0.83）,和Al_xGa_1-xAs/GaAs/Al_xGa_1-xAs/GaAs多层结构,表面镜面光亮。生长层厚度从几十到十几μm可控,测试表明外延层晶格结构完整,x值调节范围宽,非有意掺杂低,高纯GaAs外延层载流子浓度n_300K=1.7×10¹⁵cm^-3,n_77K=1.4×10¹⁵cm^-3,迁移率μ_300K=5900cmcm²/V.S,μ_77K=55500cm²/V.S。用电子探针,俄歇能谱仪测不出非有意掺杂的杂质,各层间界面清晰平直。 对GaAs,AlGaAs生长层表面缺陷,衬底偏角生长温度及其它生长条件也进行了初步探讨。     

Molecular Dynamics simulations of borate glasses

Abstract

The results of Molecular Dynamics simulations of borate glass (B₂O₃) using three-particle interactions are presented. These calculations yield a glass consisting of randomly connected BO₃ triangles. Infrared and Raman spectra have been calculated and compared with experimental spectra. The calculated infrared spectra show two main bands, one at 650 cm^?1 and one at 1250 cm^?1, in agreement with experiment. The Raman spectra reproduce the experimental peak at 805 cm^?1 but the peak width is a factor of ten too large. Apparently, the simulated glasses have less short range order than the laboratory glasses.     

Search for an isomer in94Rb

Measurements of theβ-ray half-life,γ-ray and X-ray spectra andγ-ray half-lives have been done with a plastic scintillation detector, a high resolution Ge(HP) detector and a 142 cm³ Ge(Li) detector to search for an isomeric state in⁹⁴Rb. Mass-separated activities of⁹⁴Rb were obtained from the He-jet type on-line mass-separator at the Kyoto University reactor. No isomeric transition was found in theγ-ray and X-ray measurements with the upper limits of 3×10^?4 and 8×10^?5, respectively, as compared with the 836.9 keV transition. Half-lives obtained from theγ-ray decay measurements are discussed in the light of classification given byQ _β -value measurements.     

An Infrared Method,with Reduced Solvent Consumption,for the Determination of Chlorsulfuron in Pesticide Formulations

A simple method has been developed for the determination of Chlorsulfuron in pesticide formulations by Fourier Transform Infrared (FTIR). Samples were diluted with CHCl_3^? , and the FTIR spectra of the samples and standards were obtained at a nominal resolution of 4 cm^? 1 from 4000 to 900 cm^? 1 with the accumulation of 25 scans. Chlorsulfuron determination was based on the measurement of peak area values from 1373 to 1363 cm^? 1 which were corrected by use of a two points baseline defined from 1401 to 1302 cm^? 1. The limit of detection achieved, which was of the order of 6 µg g^? 1, was appropriate for the determination of Chlorsulfuron in commercially available formulations. FTIR results were statistically comparable with those found by High Performance Liquid Chromatography (HPLC). The procedure reduces organic solvent consumption per sample to less than 3 ml CHCl₃, reduces waste generation and increases the sample measurement frequency up to 60 h^? 1.