Crystal structure and electronic structure of GaSe1−xSx series layered solids

Single crystals of GaSe1−xSx (0⩽x⩽1) series layered solids were grown by vertical Bridgman and chemical vapor transport methods. Crystal structure and electronic structure of the GaSe1−xSx (0⩽x⩽1) series layered semiconductors were characterized using X-ray diffraction and piezoreflectance (PzR) measurements. Experimental observation of the powder X-ray diffraction patterns indicated that the whole series layers including three different kinds of stacking formula with respect to the compositional change of the sulfur incorporation. Lattice constants of the GaSe1−xSx (0⩽x⩽1) are evaluated and the stacking formula for the whole series layered solids is discussed. Electronic structures of the GaSe1−xSx (0⩽x⩽1) series layer compounds are characterized using PzR measurements in the energy range between 1.9 and 6 eV at 15 and 300 K, respectively. The PzR spectra of the GaSe1−xSx (0⩽x⩽1) series layered semiconductors clearly indicated that there are five transition features observed at the band-edge as well as at the higher-energy interband transitions. The transition features for each composition of GaSe1−xSx layer compounds were analyzed and identified. The compositional dependences of the transition energies of GaSe1−xSx (0⩽x⩽1) series semiconductors were analyzed and discussed.