The physical and optical properties of GaSe_1-xS_x (0≦x≦1) series layered crystals

Ching-An Chuang^1*, Bo-Xian Yeh¹, Ching-Hwa Ho¹

¹Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan

* Presenter:Ching-An Chuang, email:d10422602@mail.ntust.edu.tw

GaSe_1-xS_x (0≦x≦0.5) series layered solids were grown using vertical Bridgman methods, and GaS was grown by chemical vapor transport (CVT) methods. The characterizations of the series layered compound semiconductor were carried out using Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Raman scattering, modulation reflectance, as well as photoluminescence (PL). The physical structures of layered GaSe_1-xS_x (0≦x≦1) crystals have both ε and β mixed phase two-layer hexagonal (2H) structure after being examined by X-ray analysis, Raman measurement as well as HRTEM measurement. Optical properties of GaSe_1-xS_x (0≦x≦1) were investigated using thermoreflectance (TR) and photoluminescence (PL). The TR and PL experimental results demonstrated that GaSe_1-xS_x (0≦x≦0.5)series are direct band gap semiconductors but GaS is an indirect band gap semiconductor. The band gaps of GaSe_1-xS_x (0≦x≦0.5) are measured at 300 K. The temperature dependence of TR for GaSe_1-xS_x (0≦x≦1) were carried out and the band gap signals showed red shift with temperature increase. For GaSe_1-xS_x (0≦x≦0.5), many near-band-edge emission features such as IBE(indirect bound exciton) , IFE(indirect free exciton), DBE(direct bound exciton) and FX(free exciton) were detected by PL experiments at 10K and these phenomena are further discussed .

Keywords: Photoluminescence, Direct band gap, GaSe_1-xS_x, Chemical Vapor Transport, Raman measurement