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Pb1-xSrxTe thin films with different strontium (Sr) compositions are grown on BaF2(111) substrates by molecular beam epitaxy (MBE). Using high resolution x-ray diffraction (HRXRD), we obtain Pb1-xSrxTe lattice constants, which vary in the range 6.462-6.492A. According to the Vegard law and HRXRD data, Sr compositions in Pb1-xSrxTe thin films range from 0.0-8.0%. The Pb1-xSrxTe refractive index dispersions are attained from infrared transmission spectrum characterized by Fourier transform infrared (FTIR) transmission spectroscopy. It is found that refractive index decreases while Sr content increases in Pb1-xSrxTe. We also simulate the Pb1-xSrxTe transmission spectra theoretically to obtain the optical band gap energies which range between 0.320 eV and 0.449 eV. The simulated results are in good agreement with the FTIR data. Finally, we determine the relation between Pb1-xSrxTe band gap energies and Sr compositions (Eg = 0.320+0.510x-0.930x2 + 184x3 (eV)).

Exploring nature of liquid structures and properties is becoming more interesting in various fundamental and applied fields. With different resorts including the resistivity method, temperature-induced liquid-liquid structure transitions (TI-LLST) have been suggested and verified to occur in some liquid alloys, while the reversibility of TI-LLST has rarely been examined as yet. Unlike some other investigated liquid alloys, here we show that electrical resistivity of Pb26Sn42Bi32 melt exhibit an anomalous change in the first heating run and a reversible change in the following cooling and heating cycles. Taking account of the structural sensitivity of electrical resistivity, the abnormal patterns suggest two sorts of TI-LLST that are irreversible and reversible in the liquid ternary alloy, respectively. This interesting phenomenon together with other growing evidence imply that liquid structures and their change characteristics are multiform and complex.

Cubic phase MgxZn1−xO/MgO multilayer heterostructures (c-MgxZn1−xO/MgO MHs) are grown on Si(100) and quartz substrates by reactive electron beam evaporation at low temperature (250°C). Cross-sectional morphology observations by field-emission scanning electron microscopy show the legible interfaces of c-MgxZn1−xO/MgO MHs. X-ray diffraction demonstrates that c-MgxZn1−xO/MgO MHs are of highly (100)-oriented. Optical transmission investigations of c-MgxZn1−xO/MgO MHs on quartz substrates reveal the coexistence of the two phases, c-MgxZn1−xO and MgO. Photoluminescence examination indicates the emergence of deep-ultraviolet emission centred at about 290 nm along with the blue shift of the ultraviolet emission from 405 nm to 396 nm when the nominal thickness of c-MgxZn1−xO well layers of MHs is diminished to 3 nm, which is probably originated from quantum confinement effect.

Single crystal PbTe thin films have been grown on BaF2 (111) by using solid source molecular beam epitaxy. The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525 degrees C by AFM show that PbTe epilayers exhibit smooth surface morphologies with atomic layer scale roughness and are crack free. It is found that for PbTe grown at 475 degrees C, the morphology is dominated by triangles and the rms roughness is 3.987 nm. Compared to the rms roughnesses of 0.432 nm and 0.759 nm for the samples grown at 375 and 525 degrees C respectively, the surface of the PbTe layer grown at 475 degrees C is much rougher. This roughening transition is due to the interaction between the elastic relaxation and the plastic relaxation during the strain relaxation process. In contrast to the result of the morphology that the PbTe epitaxial layer grown at 375 degrees C has most smooth surface, as observed from the line width of x-ray diffraction curves at higher growth temperature improves the crystal quality of the single-crystalline PbTe layer.

We report applications of a metallic film and a phase matching layer (PML) to increase the reflectivity of the cavity mirror in a long-wavelength InP-based vertical-cavity surface-emitting laser (VCSEL). The synthesis of the InGaAsP/InP distributed-Bragg reflector (DBR) with an Au film and the InP PML leads to the decrease of periods of the DBR multilayer stacks from 33 to 20 while keeping the reflectivity of the structure over 99%. The reflectivity over the whole forbidden band is significantly increased and become flatter compared to the bare DBR. The use of smaller DBR periods in a long wavelength VCSEL makes the epitaxial growth well controllable, decrease of the heat resistance, and decrease of the in-series electrical resistance of the devices. This can improve the reliability of the VCSEL growth and possibly cut down the cost of VCSEL devices.

We calculate the excitonic transition energies and exciton binding energies in ZnO/MgxZn1-xO quantum-well heterostructures with Mg composition x varied from 0.08 to 0.36. The effect of the exciton-phonon interaction on the exciton binding energies is taken into account in the model. For the ZnO/Mg0.12Zn0.88O quantum-well structure, we compare the calculated result with the available experimental data at 5 K, and a good agreement is achieved. The excitonic transition energies at room temperature in ZnO/MgxZn1-xO quantum-well heterostructures are also calculated. The results show that when the well width exceeds 50 A, the quantum size effect is neglectable and the excitonic transition energies in ZnO/MgxZn1-xO (with x varied from 0.08 to 0.36) quantum-well heterostructures are close to the value of bulk ZnO. The maximum exciton binding energy as large as 121.1 meV is obtained for the well width of 12.5 A in the ZnO/Mg0.36Zn0.64O quantum-well heterostructures.

Zinc oxide films were grown on sapphire and Si(001) substrates by reactive electron beam evaporation at low substrate temperatures. Atomic force microscopy (AFM), x-ray diffraction (XRD), and photoluminescence excitation (PLE) are employed to characterize the as-grown films. The AFM measurements have shown that all of the ZnO films present pillar-like growth properties, but the dimensional uniformity of the ZnO crystal pillars grown on sapphire was better than that on Si(001). The XRD results indicated that the prepared ZnO films both on sapphire and Si(001) were all highly c-axis oriented; the linewidths of ZnO (002) are only 0.19° and 0.28°, respectively. The PLE characterizations revealed the continuum absorption of the samples grown on sapphire. However, in the PLE spectra of the ZnO films grown on Si(001) substrates, a broad peak appears at the high-energy region, which indicates the formation of ZnO quantum dot structures on Si(001).

ZnO nanodots have been grown on Si (100) assisted by anodic aluminium oxide (AAO) template at low temperature (350 degrees C). Regular arrangement to a certain extent in local for ZnO nanodots is observed, and the average diameter of nanodots is about 9.7 nm. Photoluminescence studies at room temperature for photon energy between 2.0 and 3.6 eV reveal a strong single exciton peak at 3.274 eV (378.8 nm) with the green emission fully quenched. Narrow full width at half maximum (FWHM) of the UV emission band (0.14 eV) suggests the as-grown ZnO nanodots have a narrow size distribution.

Cubic ZnMgO thin films in the (100) orientation were grown on Si (111) substrates by reactive electron beam evaporation at low substrate temperature. X-ray photoelectron spectroscopy (XPS) analyses show that Mg content as high as 75 at.% in the cubic ZnMgO film can be obtained. Secondary ion mass spectroscopy (SIMS) measurement indicates the evidence of Mg richness in the interface between the ZnMgO film and the Si substrate, and it is probably the primary reason to form the MgO-like cubic ZnMgO structures rather than the wurtzite one. The optical band gap of cubic ZnMgO is estimated to be 5.76 eV, which was measured by the transmission spectrum of the cubic ZnMgO film grown on the sapphire substrate under the same growth condition with that on Si (111). The band gap is of 2.39 eV blueshifted compared with that of ZnO (3.37 eV), which should render applications in the fabrication of ZnMgO-related heterostructures.

PbSe films were grown on (111)-oriented BaF2 substrates by using molecular beam epitaxy. High resolution x-ray diffraction characterization showed good crystalline quality of PbSe films. Both longitudinal optical phonon at 135 cm-1 and transverse optical phonon at 47.6 cm-1 were observed by Raman scattering measurements. The Raman tensor calculation demonstrates that both transverse-optical and longitudinal-optical (LO) phonons in PbSe crystal are Raman active on (111)-oriented surface. Furthermore, 2LO phonon at about 270 cm-1 and polaron at about 800 cm-1 in PbSe, were also observed. The observed Raman frequencies are in good agreement with theoretical calculations using point ion model.

Optical studies of the CdTe/CdMnTe multiple quantum well structures with diluted manganese in barriers are presented. The combined measurements of photoluminescence and photoluminescence excitation allowed direct observation of the binding energies of n=1 heavy- and light-hole free excitons. The quantitative approach of variation of exciton binding energies with well width and barrier potential height is given. The calculated and measured exciton binding energies are in good agreement. Photoluminescence studies also show exciton-acoustic phonon scattering dominates the broadening of the exciton line width up to T = 50 K, while T > 50 K longitudinal-optical phonon scattering contributes to the line width broadening significantly.