Raman Scattering Spectrum Analysis of GaP and Its Luminous Materials^①②

The Raman scattering spectra of n-type GaP(doped S) single crystal and red and green luminous materials grown on the n-type GaP(doped S)single crystal substrate by liquid-phase epitaxy are analyed.The results show that the spectra of GaP single crystal and its luminous materials include not only the first-order longitudinal optical photons and transverse optical phonons Raman scattering peaks,but also the peaks of the bound excitons,bound electrons and bound holes.     

Temperature Dependent Raman Scattering of Phonon Modes and Defect Modes in GaN and p-Type GaN Films

Raman spectra of undoped GaN and Mg-doped GaN films grown by metal-organic chemical-vapor deposition on sapphire are investigated between 78 and 573K.A peak at 247cm－1 is observed in both Raman spectra of GaN and Mg-doped GaN.It is suggested that the defect-induced scattering is origin of the mode.The electronic Raman scattering mechanism and Mgrelated local vibrational mode are excluded.Furthermore,the differences of E2 and A1(LO) modes in two samples are also discussed.The stress relaxation is observed in Mg-doped GaN.     

Stimulated Raman Scattering in Nanorod Silicon Carbide Films

When the film is excited by a very low excitation energy, the spontaneous Raman scattering emerges. The intensity of Raman scattering is proportional to the excitation power below the threshold excitation. When the excited power reaches the excitation threshold, the intensity of Stokes light strongly increases. Meanwhile an anti Stokes light at 495 nm and multiple order but small Stokes peaks occur. The intensity of Stokes light is much larger than that of anti Stokes. The full width of half maximum (FWHM) of Stokes peak is reduced from 0.4 nm to less than 0.2 nm, the scattering angle between both Stokes and incident lights becomes less than 1°, and the angle between the Stokes and anti Stokes lights is about 3°. When the exciting power is in excess of the threshold, anti Stokes and multiple Raman scattering peaks reappear. These experiments can be unlimitedly repeated. From this experiment, we can exclude the possibility of spontaneous Raman scattering. It is suggested that the nanorods are a quantum line dimension having a large surface. There will be Raman differential scattering section so long as the nanorod films become very strong scattering media; the surface enhanced Raman scattering will be produced, the nanorod films of SiC will form a strong multiple scattering resonance cavities so as to form the stimulated Raman scattering oscillation.     

Absorption Spectrum Studies on the RDX Crystals with Different Granularity in Terahertz Frequency Range

The absorption spectrum of the cyclotrime-thylenetrinitramine(RDX)with four different particle sizes are measured in the frequency range from 0.1 THz to 2.5 THz by using the terahertz time-domain spectroscopy(THz-TDS),and the characteristic absorption peaks are acquired.All the samples are measured in a loose condition,which is very close to the real using environment of the RDX.The results show that the four kinds of samples have similar absorption peaks around the frequency of 0.82 THz,1.05THz,1.30 THz,1.46 THz,1.65 THz,and 1.95 THz.The sample with a large particle size obtains more peaks than the small one,while the peaks obtained from the sample with a small size are more protrudent.The reasons for these differences can be the refraction,scattering,and attenuation of the terahertz wave when it passes through the crystal samples.The theoretical terahertz spectrum of RDX was simulated by using density functional calculations,in which,the Becke&Perdew-Wang’s functional is used in a double numerical plus polarization method(BP/DNP).Good agreements between the experimental and computed results show that the three peaks located in the frequency of 1.30 THz,1.48 THz,and 1.96 THz are caused respectively by the twisting of three-nitrogen heterocyclic,the symmetrical oscillations of the double nitro groups,and the oscillations of a single nitro group.     

Free carrier absorption and lattice vibrational modes in bulk ZnO

The electronic properties of semiconductors are highly dependent on carrier scattering mechanisms determined by crystalline structure, band structure, and defects in the material. Experimental characteristics of lattice vibrational modes and free carrier absorption in single-crystal ZnO samples obtained from different sources are presented in this work to provide a further understanding of carrier scattering processes pertaining to electronic properties. Infrared absorption measurements indicate strong absorption peaks due to a combination of optical and nonpolar phonon modes in the 9–13 μm spectral region. The Raman spectra obtained for these samples similarly reveal the presence of these phonon modes. Infrared absorption measurements also demonstrate free carrier absorption in the 3–9 μm spectral region for higher conductivity samples, where a λ^m dependence is observed with m=2.7–3, indicating both longitudinal optical phonon scattering and ionized impurity scattering. From these results, we show that infrared absorption can be used as a routine nondestructive technique to determine the material characteristics and quality of bulk ZnO.     

Amplification Effect on Rayleigh Scattering and SBS in 25 km Distributed Fiber Raman Amplifier

The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fibers Raman amplifier have been researched. The signal source is a tunable narrow spectral bandwidth （〈10 MHz） ECL laser and is pumped by the tunable power 1427.2 nm fiber Raman laser. The Rayleigh scattering lines are amplified by fiber Raman amplifier, and Stokes stimulated Brillouin scattering lines are amplified by fiber Raman amplifier and fiber Brillouin amplifier. The SBS lines total gain is a production of the gain of Raman and the gain of Brillouin amplifier. In experiment, the gain of SBS is about 42 dB and the saturation gain of 25 Ion G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.     

Strain Relaxation Related Photoluminescence Bands in Ge／Si Short Period Superlattices

Pure-Ge/Si short period superlattice (SPS) grown by gas source MBE(GSMBE) is studied by photoluminescence spectroscopy and Raman scattering spectroscopy.An abnormal band in photoluminescence is found in an intermediate range of Lsi between 1.9nm-2.9nm for samples with Lge fixed at 1.5ml.In contrast to a pure-Ge/Si quantum well,the energy of the band shows red-shift as Lsi increases .Raman scattering shows that Si-Si vibration related Raman shift reaches a minimum for samples with strongest PL intensity of the abnormal band .It is therefore concluded that the abnormal band is related with strain relaxation process.     

Diagnostic techniques for photonic materials based on Raman and Brillouin spectroscopies

The elastic and vibrational properties of a material,bulk or planar waveguide,are studied by Brillouin and Raman spectroscopy to follow the process of nanocrystals growth in glass-ceramics. The nanoparticles cause the appearance,in the low fre-quency Raman spectrum,of characteristic peaks,whose position depends on the size of the crystals. At the same time,sharp crystal peaks,due to optical phonons,appear in the Raman spectra,allowing the determination of the nucleated phase,and a frequency shift of the Brillouin peaks is observed.     

金属有机物化学气相淀积法生长的Si掺杂GaN薄膜的应力，结构与电学特性研究

The stresses, structural and electrical properties of n-type Si-doped GaN films grown by metaiorganic chemical vapor deposition （MOCVD） are systemically studied. It is suggested that the main stress relaxation is induced by bending dislocations in low doping samples. But for higher doping samples, as the Si doping concentration increases, the in-plane stresses in the grown films are quickly relaxed due to the rapid increase of the edge dislocation densities. Hall effect measurements reveal that the carrier mobility first increases rapidly and then decreases with increasing Si doping concentration. This phenomenon is attributed to the interaction between various scattering process. It is suggested that the dominant scattering process is defect scattering for low doping samples and ionized impurity scattering for high doping samples.     

Zone-center optical phonons in wurtzite InAlN crystal

An experimental study of the optical phonons is presented for InAlN epilayers lattice-matched with GaN by means of Raman scattering,and theoretical simulations are done to investigate the zone-center optical phonons of InAlN alloy by using the modified random element isodisplacement(MREI)model.The calculated findings show that the LO and TO branches of InAlN crystal both exhibit nonlinear properties.A comparison is made between the theoretical results and the experimental data,and it shows that they are both consistent for the A 1 (LO)phonons of InAlN epilayers.     

Raman Spectra of AlP/GaP Short-period Superlatice

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Raman Scattering Spectrum Analysis of GaP and Its luminous Materials

Abstract: The Raman scattering spectra of n- type GaP(doped S) single crystal and red and green luminous materials grown on the n - type GaP (doped S) single crys-tal substrate by liquid - phase epitaxy are analyed. The results show that the spectra of GaP single crystal and its luminous materials include not only the first - order longitudi-nal optical photons and transverse optical phonons Raman scattering peaks, but also the peaks of the bound excitons, bound electrons and bound holes.     

掺杂超晶格的等离子激元与纵光学声子的耦合模

在T＝77K,测量出掺杂（Si)GaAs/AlGaAs超晶格的拉曼散射谱,观察到拉曼位移分别为223cm^-1和422cm^-1的两个光散射峰。理论分析认为,这两个散射峰是掺杂超晶格的等离子激元与纵光学声子耦合模引起的。这事模引起的光散射峰位置的理论计算值与拉曼测量结果相当一致。     

铌酸锂掺杂石英光纤拉曼增强特性研究

为了获得高拉曼增益特种石英光纤,提高拉曼光纤 放大器增益,本文研究了铌酸锂掺杂石英光纤的拉曼散射增强特性,采用改进化学气相沉积(MCVD)法制备出了铌酸锂掺杂石英光纤样品,其在1550nm 波长处的传输损耗为5dB/km。测得了铌酸锂掺杂石英光纤的拉曼光谱,并与相同长度的常 规单模光纤拉曼 光谱进行了对比,发现铌酸锂掺杂石英光纤具有更高的拉曼散射强度,在几个主要峰位处, 铌酸锂掺杂石 英光纤的拉曼散射强度为常规单模光纤的3.8～4.8倍。同时,搭建了 拉曼光纤放大器系统,分别测得铌酸 锂掺杂石英光纤和常规单模光纤的拉曼散射放大增益。实验结果表明,铌酸锂掺杂石英光纤 拉曼放大增益 约是常规单模光纤的2倍。因此,铌酸锂掺杂石英光纤作为拉曼光纤放大器的增益介质将可 取代常规单模 光纤,并能有效地提高拉曼光纤放大器的放大效果。     

InAlA5量子点材料的AFM和拉曼散射研究

对分子束外延（MBE）自组织生长的InAlAs量子点材料进行了拉曼散射实验。结合原子力显微镜（AnD对量子点形貌观察的结果,分析了InAlAs量子点生长过程中尺寸、密度和均匀性的改变,并研究了三维岛的结构对拉曼谱线的影响。对InAlAs淀积厚度不同样品的拉曼谱分析表明,岛状结构的尺寸横纵比与类GaAsLO模和类AlAs LO模的半高全宽有密切关系。不同偏振下的拉曼实验证实了该结构中的光学声子在Z（X,X）Z偏振条件下为非拉曼活性。     

Forbidden Resonant Raman Scattering in GaAs/AlAs Superlattices: Experiment and Calculations

The Raman spectra of GaAs/AlAs(100) superlattices are calculated and studied experimentally for various wave-vector directions. The experiments are performed when applying a confocal optical microscope combined with a micro-Raman spectrometer for various scattering geometries both for phonons with a wave vector directed along the normal to a superlattice and in the in-plane geometry. The frequencies and eigenvectors of phonons are calculated in the extended Born model approximation taking into account Coulomb interaction in the rigid-ion approximation. The Raman spectra are calculated in the scope of the deformation- potential mechanism; herewith, it turns out that additional peaks, which are not described in the scope of this approach, appear in the experimental spectra. It seems likely that these peaks appear due to the manifestation of Raman scattering forbidden by selection rules under resonance conditions. An attempt is made to explain the appearance of these peaks in the experimental spectra within the scope of inelastic phonon scattering at bound charges (phonons with a large dipole moment).     

表面处理对CdTe Raman散射谱的影响

利用傅利叶变换喇曼散射技术研究了CdTe表面的Raman散射谱，观察到了CdTe表面光学声子（TO、LO）的一级、二级斯托克斯、反斯托克斯Raman散射峰。实验同时还研究了经过机械抛光、化学机械抛光、化学腐蚀等不同表面处理后的CdTeRaman散射谱。实验表明Raman散射方法除可以用来表征晶体表面的完整性外，还能有效地探测样品的表面沾污情况。总的来说Raman散射技术有希望成为器件工艺过程中的一种表面无损检测手段。     

Micro‐Raman Scattering Imaging of Langmuir–Blodgett Surface Relief Gratings

Surface relief gratings (SRGs) recorded on Langmuir–Blodgett (LB) films of an azobenzene homopolymer were visualized using micro‐Raman imaging. Raman scattering (RS) was achieved using the 780 nm laser line while pre‐resonance Raman scattering (pre‐RRS) and resonance Raman scattering were achieved using the 633 and 514.5 nm laser lines, respectively. Pre‐surface‐enhanced resonance Raman scattering (pre‐SERRS) and surface‐enhanced resonance Raman scattering (SERRS) were collected for the LB films covered with a 6 nm thick silver island film. The SRG could be chemically identified by the spatial variation in the Raman signal scattered by the film due to a concentration gradient. The pre‐SERRS provided signals of the same intensity along and across the grooves, indicating that the molecular architecture at the SRG surface is the same at the peaks as in the valleys.     

Phase transition of Cu2O to CuO nanocrystals by selective laser heating

In this paper, we reported the preparation of CuO nanocrystals by microwave irradiation method. With the aid of suitable surfactants, CuO nanoparticles of uniform size and shape were successfully prepared. The as-prepared nano-products were characterized by different techniques such as Xray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM), which all confirmed the good quality of the product. However, Raman spectra showed some peaks, which were attributed to impurity phases such as Cu₂O or Cu(OH)₂. Post annealing the samples by laser is a good method to convert these phases into pure CuO. Phase transition was observed in situ by Raman spectroscopy. After laser treatment process, Raman spectra of the samples showed that the nano-product is single phase and the crystal quality of CuO nanocrystal was improved clearly.