Photoluminescence Spectra of GaS0.75Se0.25 Layered Single Crystals

Photoluminescence (PL) spectra of GaS_0.75Se_0.25 layered single crystals have been studied in the wavelength region of 500‐850 nm and in the temperature range of 10‐200 K. Two PL bands centered at 527 ( 2.353 eV, A‐band) and 658 nm (1.884 eV, B‐band) were observed at T = 10 K. Variations of both bands have been studied as a function of excitation laser intensity in the range from 8 × 10^‐3 to 10.7 W cm^‐2. These bands are attributed to recombination of charge carriers through donor‐acceptor pairs located in the band gap. Radiative transitions from shallow donor levels located 0.043 and 0.064 eV below the bottom of conduction band to acceptor levels located 0.088 and 0.536 eV above the top of the valence band are suggested to be responsible for the observed A‐ and B‐bands in the PL spectra, respectively.     

Crystal Data,Photoconductivity and Carrier Scattering Mechanisms in CuIn5S8 Single Crystals

The X‐ray diffraction has revealed that CuIn₅S₈ is a single phase crystal of cubic spinel structure. The value of the unit cell parameter for this crystal is 1.06736 nm. The crystal is assigned to the conventional space group Fd3m. The photocurrent is found to have the characteristic of monomolecular and bimolecular recombination at low and high illumination intensities, respectively. The electrical resistivity and Hall effect of CuIn₅S₈ crystals are measured in the temperature range of 50‐400 K. The crystals are found to be intrinsic and extrinsic above and below 300 K, respectively. An energy band gap of ∼1.35 eV at 0 K, a carrier effective mass of 0.2 m₀ , an acceptor to donor concentration ratio of 0.9, an acoustic phonon deformation potential of 10 eV and a nonpolar optical phonon deformation potential of 15 eV are identified from the resistivity and Hall measurements. The Hall mobility data are analyzed assuming the carrier scattering by polar optical phonons, acoustic combined with nonpolar optical phonons, and ionized impurities.     

Carrier Transport Properties of InS Single Crystals

The electrical resistivity and Hall effect of indium sulfide single crystals are measured in the temperature range from 25 to 350 K. The donor energy levels located at 500, 40 and 10 meV below the conduction band are identified from both measurements. The data analysis of the temperature‐dependent Hall effect measurements revealed a carrier effective mass of 0.95 m₀, a carrier compensation ratio of 0.9 and an acoustic deformation potential of 6 eV. The Hall mobility data are analyzed assuming the carrier scattering by acoustic and polar optical phonons, and ionized impurities.     

Effect of crystal disorder on linewidth of the Raman modes in GaS1‐xSex layered mixed crystals

The linewidths of Raman‐active intralayer compressional modes in GaS_1‐xSe_x layered mixed crystals (0 ≤ x ≤ 1) have been measured in the 10‐300 K temperature range to study the anharmonic effect as a function of compositional variation and temperature. It was found that the anharmonicity increases with an increase in substitutional disorder. The cubic (three‐phonon) processes with energy conservation is responsible for the anharmonic contribution to the broadening of the intralayer phonon lines with temperature. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low‐Temperature Raman Scattering Spectra of GaSexS1‐x Layered Mixed Crystals

Raman scattering has been used to study the vibrational spectra of GaSe_xS_1‐x layered mixed crystals at 10 K. We report the frequency dependencies of different modes on composition x, with particular emphasis on A′₁⁽²⁾ (A_1g¹) and A′₁⁽⁴⁾ (A_1g²) intralayer compressional modes having low dispersion in the Brillouin zone. The appearance of additional bands is attributed to multimode behavior typically exhibited by mixed crystals of anisotropic compounds.     

KDP晶体激光损伤机理研究

大口径KDP晶体是唯一可用作激光约束核聚变(ICF)中Pockels盒和倍频器件的晶体材料,但是低的抗激光损伤阈值使其应用受到了限制.本文从电子-空穴对的产生及稳定机制、光伤实体的本质等方面总结了多年来人们对KDP晶体激光损伤机理的研究进展,尤其从多光子电离、碰撞电离、激光加热三个方面定性阐述了电子-空穴对的产生机制, 而电子-空位对的稳定机制是探讨光损伤的关键步骤.另外从晶体生长过程及后处理两个方面初步讨论了提高光伤阈值和光学均匀性的途径.     

Electron‐phonon short‐range interactions mobility and p‐ to n‐type conversion in TlGaS2 crystals

The conductivity type conversion from p ‐ to n ‐type at a critical temperature of 315 K in TlGaS₂ crystals is observed through the Hall effect measurements in the temperature range of 200–350 K. The analysis of the temperature‐dependent electrical resistivity, Hall coefficient and carrier concentration data reveals the extrinsic type of conduction with donor impurity levels that behave as acceptor levels when are empty. The data analysis allowed the calculation of hole and electron effective masses of 0.36m ₀ and 0.23m ₀, respectively. In addition, the temperature‐dependent Hall mobility is found to decrease with temperature following a logarithmic slope of ∼1.6. The Hall mobility in the n ‐region is limited by the electron‐phonon short‐range interactions scattering with an electron‐phonon coupling constant of 0.21. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermally Stimulated Current Observation of Trapping Centers in Undoped GaSe Layered Single Crystals

Undoped p‐GaSe layered single crystals were grown using Bridgman technique. Thermally stimulated current measurements in the temperature range of 10‐300 K were performed at a heating rate of 0.18 K/s. The analysis of the data revealed three trap levels at 0.02 , 0.10 and 0.26 eV. The calculation for these traps yielded 8.8 × 10^‐27, 1.9 × 10^‐25, and 3.2 × 10^‐21 cm² for capture cross sections and 3.2 × 10¹⁴, 1.1 × 10¹⁶, and 1.2 × 10¹⁶ cm^‐3 for the concentrations, respectively.     

Atomic Force Microscopy Studies on Growth Mechanisms and Defect Formations on {110} Faces of Cadmium Mercury Thiocyanate Crystals

Growth mechanisms and defect formations on {110} faces of cadmium mercury thiocyanate crystals grown at 30°C (σ=0.24) were investigated by using atomic force microscopy (AFM). It was found that, under this condition, spiral dislocation controlled mechanism and 2D nucleation mechanism operates simultaneously and equally during growth, which is completely different from the traditional 2D nucleation and dislocation source controlled mechanisms. A number of 2D nucleus are formed at the large step terraces generated by dislocation sources, leading to the unequal growth rates of the elementary steps and thereby “step bunches” arecaused. Various defects are formed under this growth condition, which is assumed to result from the incongruence between the steps generated by different sources. A new kind of 2D defect, corresponding to one growth layer in height, was observed for the first time.     

Electrical Resistivity and Thermally Stimulated Current in CuIn5Se8

From electrical resistivity measurements in the range from 240 to 450 K and from optical absorption measurements the energy gap value of CuIn₅Se₈ has been found to be 1.13 eV. Thermally stimulated current and electrical measurements at high temperature performed in indium annealed samples show deep levels at 0.55 and 0.79 eV, respectively. These defects are expected to be associated with interstitial indium or indium in copper site because of the In‐rich condition.     

铁铪双掺铌酸锂晶体的光致散射研究

本文研究了铁铪双掺铌酸锂晶体的光致散射行为,对比了铁铪双掺铌酸锂晶体还原前后的光致散射结果.结果表明:晶体中的锂空位可使晶体暗电导增加并引起光致散射的泵浦光强阈值效应;高泵浦光强下产生的严重光致散射起源于晶体中的较高的三价铁离子浓度.铁铪双掺铌酸锂晶体具有较好的抑制光致散射的能力.     

Resonant Raman Scattering near the Free‐to‐Bound Transition in Undoped p‐GaSe

Raman spectra of GaSe layered crystal have been measured using a He‐Ne laser and temperature tuning the free‐ to‐bound gap in the range 10‐290 K. Resonance enhancement of E″⁽²⁾ mode has been observed for both incident and scattered photon energies equal to the free‐to‐bound transition energy.     

Investigation of carrier scattering mechanisms in TlInS2 single crystals by Hall effect measurements

TlInS₂ single crystals are studied through the conductivity and Hall effect measurements in the temperature regions of 100‐400 and 170‐400 K, respectively. An anomalous behavior of Hall voltage, which changes sign below 315 K, is interpreted through the existence of deep donor impurity levels that behave as acceptor levels when are empty. The hole and electron mobility are limited by the hole‐ and electron‐phonon short range interactions scattering above and below 315 K, respectively. An energy level of 35 meV and a set of donor energy levels located at 360, 280, 220 and 170/152 meV are determined from the temperature dependencies of the carrier concentration and conductivity. A hole, electron, hole‐electron pair effective masses of 0.24 m_o, 0.14 m_o and 0.09 m_o and hole‐ and electron‐phonon coupling constants of 0.50 and 0.64, respectively, are obtained from the Hall effect measurements. The theoretical fit of the Hall coefficient reveals a hole to electron mobility ratio of 0.8. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of carrier scattering mechanisms in molybdenum diselenide single crystals by hall effect measurements

Molybdenum diselenide (MoSe₂) belong to the large family of layered transition metal dichalcogenides. It consists of weakly coupled sandwiched layers i.e. Se – Mo – Se in which a Mo atom layer is enclosed within two Se layers. This structure makes MoSe₂ extremely anisotropic in character and leads to unusual structural properties. In addition, MoSe₂ possess flexible nature along with good carrier mobility to make them potential candidate for fabricating flexible high mobility electronic devices such as Schottky barrier devices, FETs, solar cell etc. In context of this authors made an effort to study the low temperature (12 < T < 300 K) electronic transport properties of Molybdenum diselenide (MoSe₂). Through the investigation the temperature dependent Hall mobility study revealed that the grown crystals of MoSe₂possess a mixed scattering mechanism. It has been found that observed temperature dependant mobility has at least two transitions from lattice to impurity scatterings showing an imprint of multicarrier nature of this semiconductor originating from its complex band structure. It has been observed that the studied crystals have at least two group of carriers of differing origins in which transition between dominant scattering mechanisms occur at different temperatures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)