Single Crystal Growth Study Of Gallium Selenide

Gallium selenide(GaSe)crystal is a nonlinear optical crystal material with excellent comprehensive performance,and it has important applications in the mid-far infrared and terahertz bands.GaSe can also be used as a two-dimensional material in optoelectronic devices,such as photodetectors,et al.In this paper,the vertical Bridgman method is used to grow GaSe single crystals,and the effects of stoichiometric ratio and annealing treatment on the crystal properties are studied through testing and analysis methods such as transient absorption spectroscopy.In this paper,a two temperature zone crystal growth furnace was designed and manufactured.The effects of crucible shape,temperature gradient and descending speed of crucible on crystal growth were analyzed.The adhesion between crystal and quartz crucible was avoided by coating carbon film on the inner wall of quartz crucible.Finally,?14×80mm GaSe single crystals were grown,and the infrared transmittance of these crystals in the500?4000 cm^-1(2.5?20?m)band is between 40?50%.In order to avoid the deviating of crystal stoichiometric ratio due to the volatilization of GaSe melt,two methods of controlling the stoichiometric ratio of GaSe were studied:(1)adding Ga₂Se₃into the GaSe melt to compensate the volatilized Se;(2)the solid-liquid-gas three-phase equilibrium method,by adding a quartz plug on the surface of the melt and adding a neck on the crucible wall,by reducing the volume of the gas-liquid interface,the vapor pressure of Se is increased and the volatilization of Se is suppressed to achieve the purpose of controlling the chemical ratio of GaSe crystals.The energy spectrum test results show that these two methods can better control the chemical composition of the crystal,and the infrared transmittance of the crystal has been improved to a certain extent.From the results of transient absorption spectrum,infrared transmittance spectrum and photoluminescence spectrum,it is found that annealing at 800?after growth can reduce the concentration of crystal defects,which is conducive to carrier migration,and improve the infrared transmittance of the crystal to 55%;annealing at 60?600?may induce the precipitation of the second phase,which leads to the decrease of infrared transmittance.