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In two-dimensional layered materials, layer number and stacking order have strong effects on the optical and electronic properties. Tungsten disulfide (WS2) crystal, as one important member among transition metal dichalcogenides, has been usually prepared in a layered 2H prototype structure with space group P63/mmc () in spite of many other expected ones such as 3R. Here, we report simultaneous growth of 2H and 3R stacked multilayer (ML) WS2 crystals in large scale by chemical vapor deposition and effects of layer number and stacking order on optical and electronic properties. As revealed in Raman and photoluminescence (PL) measurements, with an increase in layer number, 2H and 3R stacked ML WS2 crystals show similar variation of PL and Raman peaks in position and intensity. Compared to 2H stacked ML WS2, however, 3R stacked one always exhibits the larger red (blue) shift of Raman (A1g) peak and the appearance of PL A, B and I peaks at lower energies. Thereby, PL and Raman features depend on not only layer number but also stacking order. In addition, circularly polarized luminescence from two prototype WS2 crystals under circularly polarized excitation has also been investigated, showing obvious spin or valley polarization of these CVD-grown multilayer WS2 crystals. [ABSTRACT FROM AUTHOR]

Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the VCd- and the surfacestate- related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atom hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl2 annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures. [ABSTRACT FROM AUTHOR]

We demonstrate a passively Q-switched Yb3+-doped ScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4 μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics. [ABSTRACT FROM AUTHOR]