Compositional effects accompanying near equilibrium vapour growth of solid solution crystals of the types IV‐VI and II‐VI

Near equilibrium evaporation‐condensation in a sealed ampoule leads to almost full compositional reproduction of a solid solution if it consists of components having comparable vapour pressures; this can be qualitatively interpreted by domination of entropy increase. Nevertheless, even vestigial separation requires closer characteristics, since it may prove crucial – particularly for properties of semiconducting solid solutions. Maximum component separation allowed by a small temperature difference is described here in terms of thermodynamics and kinetics of solid‐vapour and vapour‐solid phase transitions. Theoretical models of the determining effects having different character are shortly described, and their applicability areas are determined. Experimental data collected for crystal growth of numerous semiconducting solid solutions of the II‐VI and IV‐VI type support the conclusion drawn from the models that the near equilibrium crystal growth from the vapour in a closed system ensures the highest degree of compositional uniformity. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dewetted growth of CdTe in microgravity (STS‐95)

Two CdTe crystals had been grown in microgravity during the STS‐95 mission. The growth configuration was dedicated to obtain dewetting of the crystals and to achieve high quality material. Background for the performed experiments was based on the theory of the dewetting and previous experience. The after flight characterization of the crystals has demonstrated existance of the dewetting areas of the crystals and their improved quality regarding the earth grown reference sample. The samples had been characterized by EDAX, Synchrotron X‐ray topography, Photoluminescence and Optical and IR microscopy. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and opto‐electronic properties of polycrystalline Cd0.96Zn0.04Te thin films

Cd_0.96Zn_0.04Te thin films are deposited onto thoroughly cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films are found to have good stoichiometry as analyzed by Rutherford Backscattering Spectrometry. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the films evaluated by AFM is 3.7 nm. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E) at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+ Δ₁ and E₂ critical points. The band gap energy of the films measured by optical transmittance measurement is 1.523 eV. The PL spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The PL line shapes give indications of the high quality of the layers.     

溶剂熔区移动法生长In∶Cd0.9Zn0.1Te晶体的性能研究

采用溶剂熔区移动法生长出掺In的Cd0.9Zn0.1Te晶体.测试了晶体轴向Zn含量分布,并对晶体的头部和中部进行了Te夹杂相、红外透过率、I-V特性曲线和PL谱图的对比测试.结果表明:头部晶体的Zn含量、红外透过率和电阻率均大于中部;而头部晶体的Te夹杂尺寸、杂质和缺陷含量均小于中部.     

Effect of substrate temperature on polycrystalline Cd0.9Zn0.1Te thin films studied by Raman scattering spectroscopy

Cd_0.9Zn_0.1Te thin films were prepared by vacuum evaporation onto well‐cleaned glass substrates maintained at 300, 373 and 473 K. X‐ray diffraction studies revealed that the films have zinc blende structure with preferential (111) orientation. Raman peak of the room temperature deposited film appeared at 140.30 cm^‐1 and 159.65 cm^‐1 were for the transverse optic (TO) and longitudinal optic (LO) phonons respectively. The XRD patterns of the higher substrate temperature deposited films exhibited an improvement in the crystallinity of the films. The Raman peak intensity increases and the FWHM decreases for the films deposited at higher substrate temperature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of Vacuum Evaporated Polycrystalline Cd0.96Zn0.04Te Thin Films by XRD,Raman Scattering and Spectroscopic Ellipsometry

Cd_0.96Zn_0.04Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X‐ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as‐deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd_0.96Zn_0.04Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3 ‐ 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points are due to interband transitions.     

Czochralski growth of Lu1‐xScxBO3:Ce solid solution crystals

Single crystals of Lu_1‐xSc_xBO₃:Ce (x=0.2, 0.3, 0.5, 0.7) were grown by Czochralski method. Continuous solid solution with calcite structure and a linear compositional dependency of crystal lattice parameter in the system Lu_1‐xSc_xBO₃:Ce are formed and their symmetry belong to hexagonal system with R3c space group checked by X‐ray powder diffraction. The electron probe micro‐analysis measurements show that the main inclusions in Lu_1‐xSc_xBO₃:Ce crystals are in the form of Sc rich oxide and Ce rich oxide. The ICP‐AES tests show that the more Sc ion content in Lu_1‐xSc_xBO₃:Ce, the smaller effective segregation coefficient of Ce in crystal will be. The X‐ray excited luminescence spectra of Lu_1‐xSc_xBO₃:Ce crystals all present a double peaked emission band with maxima round 370 and 400 nm corresponding to Ce³⁺ emission and a self trapped excitons (STE) band peaking at 269 nm. In addition, due to high density, high relative light yield, fast decay time and no‐hygroscopic property, Lu_0.8Sc_0.2BO₃:1 at%Ce crystal could be a good candidate material for scintillation application by improving the crystal quality and cerium concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optical properties of Zn(Mg,Cd)O alloy films grown by remote-plasma-enhanced MOCVD

We report the structural and optical properties of wurtzite-structure Zn(Mg,Cd)O ternary alloys. Wurtzite (0 0 0 1) Zn_1−xCd_xO and Mg_yZn_1−yO films were grown on (11–20) sapphire substrates using remote-plasma-enhanced metalorganic chemical vapor deposition. The large bowing parameters of Zn_1−xCd_xO and Mg_yZn_1−yO ternary alloys are 3.0 and 3.5, respectively, which reflects the large difference of each binary’s electronegativity. We have analyzed the broadening of photoluminescence (PL) in Zn(Mg,Cd)O alloys on alloy content by taking into account the statistical alloy fluctuation and the localization of the exciton, and have clarified that the localization of the exciton strongly affects to PL full-width at half-maximum (FWHM) in Zn(Mg,Cd)O alloys. The alloy broadenings in steady-state PL of Zn(Mg,Cd)O alloys are in good agreement with the calculated tendency by the theoretical model based on the statistical alloy fluctuation, while PL FWHM of Zn_1−xCd_xO is three times larger than the calculated results. Moreover, as another way to confirm alloy broadening, we also have done time-resolved PL measurements and derived the localized depth of the exciton in ZnO-based system, indicating a good agreement with the tendency of PL FWHM broadening.