Liquid phase growth of bulk GaSe crystal implemented with the temperature difference method under controlled vapor pressure

GaSe crystal has been expected as one of the promising nonlinear optical crystals for highly efficient terahertz (THz) wave generation. However there are several reasons why it is difficult to grow the bulk crystals with high quality. To overcome some difficulties, the temperature difference method under controlled vapor pressure (TDM-CVP) is applied for crystal growth. According to this method, stoichiometric composition can be controlled by the application of Se vapor during crystal growth. Crystal growth is carried out at a constant growth temperature without any mechanical disturbance or vibration. It is also noticed that lower temperature growth enables the reduction of point defect concentration in equilibrium. In this article, surface morphology is observed by an optical microscope using the Nomarski interference method. To identify polytypes of grown crystals, backscattered Raman spectra were measured. X-ray diffraction confirmed the polytypes and single crystalline phase. Infrared (λ=1 μm) and terahertz wave (1-3 THz) transmittance measurements were performed to calculate the absorption coefficient in these wavelength regions. From these results, it is shown that the grown crystals have shown ε-type single phase and the absorption coefficients of grown crystals have been improved according to the increase of applied Se vapor pressure during crystal growth.