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Atomic force microscopy (AFM) and power-dependent micro-photoluminescence (μ-PL) spectroscopy are used to study the structure and exciton energy states in InAs quantum dots (QDs) grown on an In0.35Ga0.65As template on GaAs (311)B. The In0.35Ga0.65As template, consisting of a two-dimensionally modulated layer of closely packed connected cells, has a remarkable effect on the optical properties of the InAs QDs. By comparing the emission spectra of the samples without and with InAs QDs and the work carried out by Gong et al. [J. Cryst. Growth 251 (2003) 150; Appl. Phys. Lett. 81 (2002) 3254] we conclude that the existence of the In0.35Ga0.65As template enhances the photo-absorption and therefore the exciton emission from the QDs due to efficient exciton transfer from the template into the QDs. Furthermore, the PL emission from the QDs clearly reveals four discrete energy levels, S, P, D, and F with increasing excitation power.

The reentrant spin glass behaviour was observed in half doping (La,Pr)1/2Ca1/2MnO3 manganites with a CE-type antiferromagnetic structure. It shows sequential multiple magnetic transitions from the paramagnetic to the ferromagnetic, antiferromagnetic, spin glass (SG) transitions, which reflects the complex magnetic interaction in the ground state of manganites. This can be explained by the competition interaction between the ferromagnetic and the CE-type antiferromagnetic matrix, and the disorder due to the tolerance factor t and A-cation size variance ?2. The results reveals the coexistence of ferromagnetic clusters and SG clusters in the background of the antiferromagnetic matrix in the ground state of half doping (Pr,La)1/2Ca1/2MnO3 systems.

In this paper the nucleation and growth processes of GaAs(001) molecular-beam epitaxy were studied by Monte Carlo simulation. The density of islands and the density of isolated Ga adatoms were obtained for different growth temperatures, and the island size distribution at low coverage, as well as the correlation function between atoms and its relation with the temperature were studied in detail.

We report the far-infrared photoconductivity spectroscopy (FIRPCS) of the high purity n-GaAs grown by molecular beam epitaxial (MBE) technique. The current-voltage (I-V) measurement and FIRPCS under different electric field strength have been performed on high purity n-GaAs at 4.2 K. Except for photothermal ionization process, a new far-infrared photoconductivity (FIRPC) mechanism is observed. This photo ionization process is assisted by impact ionization and depends on external electric field. This new mechanism originates from photo-field ionization.

The behaviour of doped impurity in poly (3-methyl thiophene) - P3MT has been studied by Raman, photoluminescence (PL) and photoreflectance (PR) spectroscopies. It is experimentally demonstrated that the behaviour of doped impurity in conducting polymer P3MT is different from that in conventional inorganic semiconductors. The doped impurity is located at the spaces between the molecular chains in P3MT film and the band gap of P3MT increases with doping density.

An empirical relation between the localization of impurity local modes, and the mass defect factor is obtained by calculating the local density of states (LDOSs) of the impurity and its surrounding atoms in a semiconductor. Based on this empirical relation, the calculation of the frequency of local mode by the mass defect model including the localization effect shows a good agreement between the theoretical and experimental results.

Impurity centres in high purity silicon with ionization energies 38.32 and 40.09meV are observed by photothermal ionization spectroscopy measurements. Their typical shallow donor characteristics are approved by good agreement with theoretic evaluation under varying magnetic fields. The 2p0 state lifetime of one donor centres are more than 3 times longer than that of phosphorus in the same silicon sample. Compared to phosphorus which has been already successfully exploited to produce silicon-based THz radiations, this shallow donor centre has a pronounced enhancement on lifetime and quality factor of population inversion level. Hence, silicon with this donor centre would be a potential excellent candidate to develop improved silicon-based THz sources.

The optimum photo-thermal ionization range near liquid helium temperature for the shallow impurities in n type high purity silicon single crystal was determined experimentally. At temperature within this range, the high resolution photo-thermal ionization spectra (PTIS) of this sample were measured. Positive PTIS responses from the majority residual impurity phosphor (P) and compensating impurity boron (B) were observed by simultaneously irradiating the sample with far infrared and band-edge light. Under action of applied external magnetic fields, the positive response from compensating impurity B changes to negative response. The posibility of these phenomena being the result of temperature effect was excluded, which revealed the deficiency of Darken model and supported the model of rapid recombination of minority carriers for PTIS response of compensating impurity in elemental semiconductors.

The results of high sensitivity photo-thermal ionization spectroscoic (PTIS) investigation of shallow acceptors in high purity p-type germanium sample with room temperature resistivity of about 50Ω·cm, at temperature above liquid helium by Fourier transform spectrometer and associated magneto-optical measurement systems, are reported. The optimum photo-thermal ionization temperature range for the shallow impurities in high purity germanium is determined experimentally. At temperatures within this range, the PTIS spectra of this sample were measured. Boron and aluminum are found to be the main shallow acceptors in the sample. The causes of line splits of spectra, rapid recombination of compensating impurity and random strain, are analyzed and discussed.

We have investigated two types of Zn1-xCdxSe quantum islands in CdSe/ZnSe heterostructure with different size and Cd composition using micro-photoluminescence and micro-Raman spectroscopy. The micro-photoluminescence spectra at 4.2 K indicate that the photoluminescence peaks of the islands have a large red-shift of 166 meV when the thickness of CdSe deposition layer increased from 1.8 ML to 2.3 ML, which can't be explained by considering the change of quantum confinement potential only. We also found two other important mechanisms which may lead to the large red-shift by comparing the micro-photoluminescence and micro-Raman spectra. First, the sheet density of large Zn1-xCdxSe islands which have lower exciton ground state energy will increase and the large islands will dominant gradually the photoluminescence properties of the samples with increasing thickness of the CdSe layer. Second, the increase of Cd composition in the Zn1-xCdxSe quantum islands contributes to the large red-shift as well. This is verified by resonant Raman scattering spectra of the samples.

We have investigated the temperature_dependent photoluminescence of two types of quantum islands in ultrathin CdSe/ZnSe layers. At low temperatures, excitons in these two types of quantum islands can transfer by tunneling. The hopping process of the localized excitons gradually becomes the dominant mechanism with increasing temperature. We found that the small islands are nano_scale clusters with quasi_zero_dimensional properties, which are different from those of the large islands. Experiments indicated that these two types of islands are optically correlated although their excitonic properties are different.

Using the material chip technology,large area photodiodes of n-on-p structure with different boron implantation dose are fabricated on the Hg1-xCdxTe film for mid-infrared wavelength region(x=0.291).Current-voltage characteristics of the photodiodes are measured at 77K and zero bias resistance-area products of different photodiodes are fitted from the data in the voltage range of -0.2—0.08V.The study indicated that the R0A products of different elements depended distinctly upon the implanted boron dose.A large R0 value has also obtained in another chip with x=0.2743.All the samples in this study are grown by Riber 32P molecular-beam epitaxy system and all the junctions-forming process is same to the standard planar technology but using a series of metallic masks during the boron ion implantation.

The photocurrent spectra characteristics of the 15μm very long wavelength GaAs/AlGaAs quantum well infrared photo detector(QWIP) have been investigated.The two photocurrent response peaks, which have a Gaussian lineshape due to the random fluctuation of the well width,are attributed to the transitions from the ground state E0 to the first excited state E１ and the third excited state E3 in the well,respectively.The transition peaks shift linearly to higher energy as the bias across the detector increases.Taking into account electrons exchange effect,we find that the theoretical calculation using the transfer matrix method agrees well with the experimental data.

We report the growth of Bi2Ti2O7 thin films on n type Si substrates by the chemical solution decomposition technique. Both the X-ray double-crystal diffraction and atomic force micro spectroscopy measurements are used to check the film properties. It is shown that the film is a multi crystal film dominated by the Bi2Ti2O7 phase. The C-V measurements are also performed on Au/Bi2Ti2O7/n-Si(100) MOS structure. It is revealed that both the fixed and mobile negative charges are contained in the film. The mobile negative charge results in the hysteresis loops on C-V curve.

We have studied the carrier concentration and the mobility in GaN expitaxial thin films deposited on sapphire substrate using infrared reflection spectroscopy. By theoretical calculation and fitting with the experimental IR reflection spectra for a series of Si-doped GaN epilayers and the sapphire substrate, we obtain the phonon vibrating parameters and plasmon frequency and damping constant in GaN. The carrier concentration and mobility have been deduced. The results show that the data for carrier concentration coincide with Hall measurement while the mobility is lower than Hall data by a factor of about 0.5. The variation of the LO phonon-plasmon coupling mode with doping level has been clearly observed. Raman measurement has been performed on the same series of samples, showing that the behavior of the LO phonon-plasmon coupling mode is similar to that in IR measurement.

This paper reports the molecular beam epitaxy growth of the GaAs single crystal film on the perovskite oxide SrTiO\-3(001) substrate. The photo modulated reflectance spectroscopy and the photoluminescence measurement show that the energy band gap and optical property of the GaAs single crystal film on the SrTiO\-3 substrate is similar to that of the GaAs bulk material and the broadening of band\|to\|band emission of the GaAs epitaxial film is 5 times that of the GaAs single crystal. PACC: 6855; 8110; 8115; 7125

The electron effective masses, scattering time and mobilities near the Fermi level for the lowest two subbands of the two-dimensional electron gases in a pseudomorphic In0.80Ga0.20As/In0.53Ga0.47As/In0.52Al0.48AsHEMT structure are determined by fitting the cyclotron resonance spectra. The significant enhancement of the electron effective masses, resulting from the conduction band nonparabolicity and the wave function penetration, is observed. The evident subband dependencies of the electron scattering time and mobilities dominated by the alloy scattering and ionized impurities scattering are also discussed.

The resonant subband-Landau-level coupling(RSLC) between the N=1 Landau level of the lowest subband and the N＝0 Landau level of the subbands with quantum index up to i＝5 of two-dimensional electron gases in GaAs/AlGaAs heterojunction was observed under relatively low magnetic field.Several intersubband energies were accurately determined. The experimental results were in good agreement with the self-consistent calculations including the depolarization shift and exciton-like effect corrections.The quantum index dependence of the level splitting due to the RSLC was discussed.

Photoconductivity (PC) spectra of impurities in n type GaAs under magnetic field are presented. The resonant interaction between high excited states of bound electrons and LO phonons under relatively low magnetic field was observed. The magnetic field dependency of PC response of resonant polaron and the physical origin of the PC peak stuck on the energy position of LO phonon are discussed.

A Series of samples of ultra thin AlGaAs films grown on GaAs(100) substrate by MBE are studied by photomodulated reflectance (PR)spectroscopy in ultra high vacuum chamber.More than one peak are observed for samples with thickness less than 35nm,but only one peak is observed for 100nm thick sample,The position and width of these peaks change with sample thickness.The experimental results are well explained by step potential model.

The 2p± and 3p± excited lines of P donors in Si0.92Ge0.08 epitaxial layer have been observed using photothermal ionization spectroscopy.The ionization energy of P in Si0.92Ge0.08 is 45.51meV according to effective mass approach.The spectral lines of P in Si1-xGex compared with those in pure Si apparently broaden due to alloy disorder effect.

The room-temperature photoluminescence (PL) spectrum of the modulation-doped strained In0.60Ga0.40As/In0.52Al0.48As multiple quantum wells (MQW) is reported. In addition to two strong PL peaks related to the recombination between electrons in the first (n = 1), second ( n = 2) subbands and heavy holes in the first ( n = 1) subband, a weak PL shoulder related to the recombination between n = 1 electrons and n = 1 light holes is obsevered at low temperatures. We demonstrate that the main mechanism of the decrease in radiative QW recombination efficiency is due to the carrier trapping on the misfit dislocations, based on the temperature and excitation power dependence of the PL peak intensity and energy and the steady-state PL model.

The calculation method of quantum chemistry has been extended to describe the lattice instabilities and the nature of the lattice instabilities of hexahalometallates. Some interesting calculation results have been obtained and compared with the exper-imental results obtained by Raman and Brillouin scattering.

We report direct experimental determination of the wavefunction mixture and composition for hybridized Zeeman states of P in Si. The intensity evolution of the Zeeman transitions nearby anti-crossing region for the isolated P donors in high pure Si bas been measured quantitatively by use of high sensitive and high resolution photothermal ionization spectroscopy (PTIS); The wavefunction compositions and their evolutions upon magnetic field for the hybridized Zeeman states of bounded electrons of impurities have been deduced from the measurement. A variational calculation under the frame of effective mass approach has been performed to estimate theoretically the wavefunction composition. The results are campare with experimental ones.

The transmission spectra of p-PbTe have been measured by the strip-line technique with different far infrared laser wavelengths at different anhgles of the direction of maqnetic field relative to the crystal axis at low temperature of 1.5 k. A strong influence of mode coupling on strip-line transmission spectra has been observed and analyzed. The final results extracted from experimental spectra by numerical simulation are in good agreement with the six band k·p model calculation.

Using diamond-anvel cell high pressure equipment, the phase transition of Cd1-xMnxSe under high pressure has been measured by optical absorption and X-ray diffraction methods, It has been found that the phase transition is irreversible. Under common pressure, Cd1-xMnxSe has wurzite structure, but it transforms to Nad structure under high pressure. When the pressure is removed, Cd1-xMnxSe becomes zinc blend structure. In addition, the relation between the pressure of phase transition and component x is also obtained.

The far infrared reflection spectra of Hg1-xMnx Te with different composition in the temperature region of 4.2-300 K are reported. It is demonstrated that there are a gap mode as well as a local mode associated with impurity Mn in HgTe. The gap mode has a frequency of 97 cm-1. The theoretical analysis of the gap mode has been proceeded.

The far infrared reflectances of the high-Tc superconductor YBa2Cu3O9−δ(Tc=90k) are measured in the frequency range 25–150 cm−1 and the temperature range 42k-200k. The reflectance curve with 42k rapidly drops near 125 cm−1, whereas the curves with T>90k go smoothly. It indicates such superconductors have a energy gap 2Δ=15.5 mev, and the ratio 2Δ/kTc=2.0 is close to that of superconductors La-Ba-Cu-O and La-Sr-Cu-O, but well smaller than the BCS value 3.5.

We report here the acoustic local mode and TA band mode for the lattice vibration of the mixed crystals Cd1-xMnxTe as observed by very far infrared spectra. The occurence of the acoustic local mode and the weakly optical activity of TA mode induced by crystalline-mixing are discussed in light of the defect lattice dynamics.

The micro-photoluminescence(μ-PL) scan has been performed on a single V-groove GaAs/AlGaAs quantum wire in the direction perpendicular to the wire.The variatio n of μ-PL spectra from various quantum structures with different spatial positi ons has been observed.In the region of quantum wire (QWR) the PL spectra contain the peaks from QWR,necking quantum well (NQWL) and vertical quantum well (VQWL) ,while in the area about 1μm and farther away from the QWR the PL spectra show the peaks from side-wall quantum well (SQWL) and top quantum well (TQWL).All the scanned PL spectra have been fitted by Gauss line shape.The asymmetric PL peaks of QWR and SQWL were decomposed into two components which were ascribed to the optical transitions between the electron ground state in the conduction band and the heavy hole and the light hole ground states in the valence band.The variati on of PL intensity from luminescent components with the spatial positions direct ly demonstrates the origin of the photoluminescence relating to different quantu m structures,and reflects the carrier transfer from SQWL to QWR,resulting in th e PL quenching of SQWL.

We perform the micro-photoluminescence measurement at low temperatures and a scanning optical mapping with high spatial resolution of a single V-grooved GaAs quantum wire modified by the selective ion-implantation and rapid thermally annealing. While the mapping shows the luminescences respectively from the quantum wires and from quantum well areas between quantum wires in general, the micro-photoluminescence at liquid He temperatures reveals a plenty of spectral structures of the PL band for a single quantum wire. The spectral structures are attributed to the inhomogeneity and non-uniformity of both the space structure and compositions of real wires as well as the defects nearby the interface between quantum wire and surrounding quantum well structures. All these make the excitons farther localized in quasi-zero-dimensional quantum potential boxes related to these non-uniformity and/or defects. The results also demonstrate the ability of micro-photoluminescence measurement and mapping for the characterization of both opto-electronic and structural properties of real quantum wires.

Photoluminescence (PL) spectra of annealed a-SixC1-x:H films were studied. The-widths of the exponential bandtails were determined by means of the temperature dependences of PL peak energy positions. The experimental results shows that PL peak energy positions shift towards the lower energy with annealing temperature increasing. The bandtail widths have been calculated according to the exponential bandtail model, the calculation shows that the bandtails contract with increase of annealing temperature. A discussion about the results has been given.

The absorption edge of p-Hg1-xCdxTe with x = 0.7 has been measured at different pressures in the range of 0-36kbar and room temperature. The experimental energy gap is basically in agreement with the result calculated by empirical formula The first order pressure coefficient of Hg1-xCdx Te obtained by a least square fitting to experimental data under different pressures is a = 8.7×10-11eV/Pa, which can be explained by chemical bond dielectric function theory. The second order pressure coefficient of energy gap has also been obtained experimentally as β= -6.3×l0-13eV/ kbar which is hard to understand theoretically. In addition, a structural phase transition has been found under 34-36kbar.

The far infrared reflection spectra of n-GaAs_(1-x)P_x with x= 0.328 and x = 0.40 are investigated in the frequency range of 40-700 cm~(-1) and the temperature range of 4.2-300 K. The important physical parameters describing the optical phonons, plasmon and LO phononplasmon coupling mode of the material and infrared optical constants are obtained by the multioscilla-tor fitting and K-K relation calculation. A model of two conduction band valley with a donor level below and associated with X minimum is presented to explain the behavior of the dependence of plasmon frequency on temperature and the variation of the three coupling modes with temperature.

We report here for the first time a two stage nonmagnetic high pressure equipment foi studying various transport phenomena. The structure and the principle of the design are described. the experimental results are presented. A completely hydrostatic pressure of 28 kbar is obtained. With this equipment, the resistivity and Hall coeffecient for Ge, InSb and HgCdTe have been measured under pressure up to 25 kbar. The energy gaps and the carrier mobilities as functions of pressure for these materials have been determined, the results are in good agreement with those of other experiments.

We report the experimental set-up and measurement system combining with a fast-scan Fourier transform spectrometer for photothermal ionization spectroscopy. They have been successfully applied for the investigation and detection of residual shallow impurity centers in ultra-pure germanium and silicon single crystals with high resolution as well as high sensitivity. Boron acceptor at a concentration of the order of magnitude of 108 cm-3 has been detected in ultra-pure germanium, and the detection limit of at least 107 cm-3 has been demonstrated. Lithiumoxygen donor complex D(Li, O) has been revealed in n-type highpurity silicon. Transition line series of both boron acceptor and phosphorus donor in p-type high-purity silicon have been observed simultaneously with the excitation of intrinsic light. In addition, the transitions associated with higher excited states of shallow impurities in both germanium and silicon have also been observed.

Far-infrared reflection spectra in the wavenumber region between 15 to 500 cm-1 are obtained and studied for the mixed crystals CdxHg1-xTe with different compositions from 0.18 to 0.45 at the temperatures between 4.2 to 300 K. In addition to the fine structures of the CdTe-like optical phonon reflection band, the complex structure of the HgTe-like band for the low composition sample has been observed, and the dependences of the spectral structures on the composition and the temperature of the samples have also been investigated. The fine structures of the reflection spectra are explained based on the multimode quasi-harmonic oscillator model.By means of the classical oscillator matching method, the curve-fitting calculations are performed for the experimental reflection spectra, and the dielectric function spectra and other optical constants versus frequencies are obtained from a satisfactory fitting.

We report here the photoreflectance spectra of the conducting polymer. The interband transition and the transition associated with bipolaron have been observed for the poly (3-mythyl thiophene)-P3MT with different doping densities and under different temperatures, different intensities of modulation light. It was also demonstrated experimentally that the bipolaron may be induced by light with photon energy larger than the band gap Eg of the material, the bipolaron is the intrinsic elementary excitation state which is independent on the way of inducement ( photoinduced or doping-induced); bipolaron may be pinned by ionized impurity and then the confinement parameter will be increased.

The photoluminescence spectra of conducting polymer P3MT with different doping densities at different excitation intensities and temperatures are reported. It is demonstrated experimentally that there are three kinds of radiative transitions, i.e., direct interband transition, recombination of exciton and radiative transition between polaron level and edge of band for the conducting polymer P3MT with nondegenerate ground state.

We report here the far infrared absorption and reflection spectra of the mixed crystals ZnxCd1-xTe with small x in the temperature range of 4.2-300 K and the frequency region of 20-350 cm-1. The local and quasi-local modes induced by Zn and ZnTe in CdTe and the CdTe-like 2TA two-phonon absorption are observed. The frequencies of the modes are estimated by useing the mass-defect model combined with Green's function method. The random element isodisplacement (REI) model is used to calculated the two mode behaviors of the mixed crystals and to best fit the reflection spectra. Besides, the temperature dependence of the phonon absorption and the relaxation factor of CdTe-like and ZnTe-like modes are calculated and explained.

The effect of pressure on the optical absorption edge for mixed crystals Cd1-xMnxTe with different manganese concentrations in the range of lbar to 40 kbar and at room temperature is reported. The observed absorption edge shifts to higher energy with increasing pressure at a rate of a = 6-8 ×10-3 eV/kbar and a second order coefficient with the order of magnitude 10-5 eV/kbar2 for the samples with x-3 eV/kbar for the samples with x≥0.5. A phase transition from zinc blende to NaCl-type structure occurs for all the samples studied. The transition pressures depend on the Mn contents in the samples in the region of 25—40 kbar. The physical origins of different pressure coefficients are discussed in the light of the deformation potentials of energy band slates and the hybridization of the Mn2+ 3d levels with the p-like states in the valence band.

We report here the results of far infrared absorption on spectra of mixed crystal Cd1-xMnxTe with different compositions x in wavenumber region of 20 to 400cm-1 and temperature region of 4.2 K to 300 K. The CdTe-like, MnTe-like reststrahlen bands and their LO-TO splitting have been resolved. A low frequency absorption band for all the samples and a quasi-local mode absorption peak for the sample with low x value have been found for the first time in the low frequency side of reststrahlen band. In addition, several two-phonon bands have also been observed on both sides of reststrahlen band. The appearence and the position of the quasi-local mode have been estimated with the lattice dynamics of defects. Other absorption bands and their probable origin have also been discussed.