Raman scattering study on diluted magnetic semiconductor Ga1-xMnxAs prepared by Mn-ion implantation

Raman scattering measurements have been performed in diluted magnetic semiconductor Ga1-xMnxAs prepared by Mn-ion implantation, deposition, and post-annealing technique. It is found that the Raman spectrum measured from the implanted surface of the sample shows some new weak modes in addition to the GaAs-like modes which are observed from the unimplanted surface. The new vibrational modes observed are assigned to MnAs-like modes. The coupled LO-phonon plasmon mode, and Mn and As related vibrational modes caused by Mn-ion implantation, deposition, and post-annealing are also observed. Furthermore, the GaAs-like modes are found to be shifted by approximately 4 cm(-1) in the lower frequency side, compared with those observed from the unimplanted surface.

Raman scattering study on vibrational modes in Ga1-xMnxN prepared by Mn-ion implantation

Raman scattering measurements have been carried out on ferromagnetic semiconductor Ga1-xMnxN prepared by Mn-ion implantation and post annealing. The Raman results obtained from the annealed and un-annealed Ga1-xMnxN demonstrate that crystalline quality has been improved in Ga1-xMnxN after annealing. Some new vibrational modes in addition to GaN-like modes are found in the Raman spectra measured from the Ga1-xMnxN where the GaN-like modes are found to be shifted in the higher frequency side than those measured from the bulk GaN. A new vibrational mode observed is assigned to MnN-like mode. Other new phonon modes observed are assigned to disorder-activated modes and Mn-related vibrational modes caused by Mn-ion implantation and post-annealing. (c) 2006 Elsevier Ltd. All rights reserved.

Photoluminescence and Raman scattering correlated study of boron-doped silicon nanowires

Boron-doped (B-doped) silicon nanowires (SiNWS) have been prepared and characterized by Raman scattering and photoluminescence (PL). B-doped SiNWS were grown by plasma enhanced chemical vapor deposition (PECVD), using diborane (B2H6) as the dopant gas. Raman spectra show a band at 480cm(-1),which is attributed to amorphous silicon. Photoluminescence at room temperature exhibits three distinct emission peaks at 1.34ev, 1.42ev, 1.47ev. Possible reason for these is suggested.

Raman scattering study of vibrational modes and hole concentration in GaxMn1-xSb

The Raman scattering study of vibrational modes and hole concentration in a ferromagnetic semiconductor Ga1-xMnxSb grown by Mn ion implantation, deposition and post-annealing has been presented. The experiments are performed both in implanted and unimplanted regions before and after etching the samples. The Raman spectra measured from the unimplanted region show only GaSb-like phonon modes. On the other hand, the spectra measured from the implanted region show additional phonon modes approximately at 115, 152, 269, 437 and 659 cm(-1). The experimental results demonstrate that the extra modes are associated with surface defects, crystal disorder and blackish layer that is formed due to Mn ion implantation, deposition and annealing processes. Furthermore, we have determined the hole concentration as a function of laser probing position by modeling the Raman spectra using coupled mode theory. The contributions of GaSb-like phonon modes and coupled LO-phonon plasmon mode are taken into consideration in the model. The hole-concentration-dependent CLOPM is resolved in the spectra measured from the implanted and nearby implanted regions. The hole concentrations determined by Raman scattering are found to be in good agreement with those measured by the electrochemical capacitance-voltage technique.

Short range scattering mechanism of type-II GaSb/GaAs quantum dots on the transport properties of two-dimensional electron gas

We have studied the scattering process of AlGaAs/GaAs two-dimensional electron gas with the nearby embedded GaSb/GaAs type-II quantum dots (QDs) at low temperature. Quantum Hall effect and Shubnikov-de Haas oscillation were performed to measure the electron density n(2D), the transport lifetime tau(t) and the quantum lifetime tau(q) under various biased gate voltage. By comparing measured results of QDs sample with that of reference sample without embedded QDs, mobilities (transport mobility mu(t) and quantum mobility mu(q)) dominated by GaSb QDs scattering were extracted as functions of n(2D). It was found that the ratios of tau(t) to tau(q) were varying within the range of 1-4, implying the scattering mechanism belonging to the sort of short-range interaction. In the framework of Born approximation, a scattering model considering rectangular-shaped potential with constant barrier height was successfully applied to explain the transport experimental data. In addition, an oscillating ratio of tau(t)/tau(q) with the increasing n(2D) was predicted in the model.

On the radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas

The radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas of finite depth is investigated. The analytical expressions for the radiated and diffracted potentials are derived as infinite series by use of the method of separation of variables. The unknown coefficients in the series are determined by the eigenfunction expansion matching method. The expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are given and verified by the boundary element method. Using the present analytical solution, the hydrodynamic influences of the angle of incidence, the submergence, the width and the thickness of the structure on the wave forces, hydrodynamic coefficients, and reflection and transmission coefficients are discussed in detail.

Experimental study on polarization holographic storage in genetic mutant BR-D96N film

Recording with both parallel and orthogonal linearly polarized lights, polarization holographic storage in genetic mutant BR-D96N film is reported with both transmission type geometry and reflection type geometry. Polarization properties of diffraction light and scattering light are discussed for two different cases, parallel polarization recording and orthogonal polarization recording. It shows that, compared with recording with parallel polarization lights, orthogonal polarization holography can separate the diffraction light from the scattering noise, therefore improving the signal-to-noise ratio. It also shows that, compared with reconstruction with reference light, reconstruction with phase conjugated wave of the reference light can improve the signal-to-noise ratio of the reconstructed diffraction image, and also the wave-front aberration of the object light introduced by irregular phase object in the optical pass-way can also be corrected effectively, which ensures that the reconstructed diffraction image has a better fidelity. The preliminary angle-multiplexed volume holographic storage multiplexed by transmission type geometry and reflection type geometry is demonstrated in the BR-D96N film. Experiment shows that there is no cross-talk between the two pages of images except for some scattering noises.

Transient and nonlinear analysis of slow-light pulse propagation in an optical fiber via stimulated Brillouin scattering

We investigate slow-light pulse propagation in an optical fiber via transient stimulated Brillouin scattering. Space-time evolution of a generating slow-light pulse is numerically calculated by solving three-wave coupled-mode equations between a pump beam, an acoustic wave, and a counterpropagating signal pulse. Our mathematical treatments are applicable to both narrowband and broadband pump cases. We show that the time delay of 85% pulse width can be obtained for a signal pulse of the order of subnanosecond pulse width by using a broadband pump, while the signal pulse is broadened only by 40% of the input signal pulse. The physical origin of the pulse broadening and distortion is explained in terms of the temporal decay of the induced acoustic field. (C) 2009 Optical Society of America

Reducing group-velocity-dispersion-dependent broadening of stimulated Brillouin scattering slow light in an optical fiber by use of a single pump laser

We propose a method of effectively extending the stimulated Brillouin scattering (SBS) gain bandwidth in a single-mode optical fiber to reduce group-velocity-dispersion (GVD)-dependent pulse spread of SBS slow light. This can be done by overlapping doublet SBS gain spectra synthesized from a single pump laser. Numerical calculations are performed to verify our proposed method. We find that there exists the optimum spectral separation between two center frequencies of the doublet SBS gain spectrum with respect to the inherent spectral width of the pump laser, which makes it possible to effectively reduce the signal pulse broadening due to GVD. We show that the maximum time delay of the amplified signal pulse can be approximately two times longer than that by a previously reported method using a single broadband pump laser. (c) 2008 Optical Society of America.

Fast calculation technique for scattering in T-matrix method

In scattering calculations using the T-matrix method, the calculation of the T-matrix involves multiplication and inversion of matrices. These two types of matrix operations are time-consuming, especially for the matrices with large size. Petrov et al. [D. Petrov, Y. Shkuratov, G. Videen, Opt. Lett. 32 (2007) 1168] proposed an optimized matrix inversion technique, which suggests the inversion of two matrices, each of which contains half the number of rows. This technique reduces time-consumption significantly. On the basis of this approach, we propose another fast calculation technique for scattering in the T-matrix method, which obtains the scattered fields through carrying out only the operations between matrices and the incident field coefficient. Numerical results show that this technique can decrease time-consumption by more than half that of the optimized matrix inversion technique by Petrov et al. (c) 2008 Elsevier B.V. All rights reserved.

Two-component model for the interstellar scattering in direction to the Vela pulsar

This paper discusses a rigorous treatment of the refractive scintillation of pulsar PSR B0833-45 caused by a two-component interstellar scattering medium. It is assumed that the interstellar scattering medium is composed of a thin screen ISM and an extended interstellar medium. We consider that the scattering of the thin screen concentrates in a thin layer presented by a delta function distribution and that the scattering density of the extended irregular medium satisfies the Gaussian distribution. We investigate and develop equations for the flux density structure function corresponding to this two-component ISM geometry in the scattering density distribution and compare our result with that of the Vela pulsar observations. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation of the Vela pulsar than does the single extended medium model. The level of refractive scintillation is strongly sensitive to the distribution of scattering material along the line of sight. The logarithmic slope of the structure function is sensitive to thin screen location and is relatively insensitive to the scattering strength of the thin screen medium. Therefore, the proposed model can be applied to interpret the structure function of flux density observed in pulsar PSR B0833-45. The result suggests that the medium consists of a discontinuous distribution of plasma turbulence embedded in the Vela supernova remnant. Thus our work provides some insight into the distribution of the scattering along the line of sight to the Vela pulsar.