Growth And Characterization Of ZnSe Crystals By Traveling Heater Method

ZnSe crystals is one of the most important Ⅱ-Ⅵ compound semiconductor materials.ZnSe and its solid solution are widely used in mid-infrared lasers,high-energy radiation detection,blue LED,optical communication,and so on.However,due to its high melting point and high vapor pressure,it is still a huge challenge for growing ZnSe crystals with high crystalline quality.In this thesis,the traveling heater method（THM）have been adopted to grow ZnSe crystals,and the structural defects and photoelectric properties for THM-grown ZnSe crystals were systematically studied.ZnSe crystals were grown by THM with different growth conditions（the growth temperature,growth rate,ACRT,etc.）,and the effects of these growth parameters on the THM growth process of ZnSe crystals were revealed.Finally,ZnSe single crystals were successfully obtained by using the optimum growth parameters,which were the growth temperature of 900?C,the growth rate of 2.4 mm/day,the molten zone with a length of 15 mm,and ACRT with a maximum rotation speed of 15 rpm.The relationships among the growth interface morphologies,growth parameters and structural defects were revealed by analyzing ZnSe crystals by THM with different conditions.The results indicated that for without ACRT,the shape of the growth interface in macro-scale was concave,and after introducing ACRT with a maximum rotation speed of 10 rpm,a flat growth interface in macro-scale was obtained.By further increasing the maximum rotation speed to 20 rpm,the shapes of the growth interface were changed from flat to slightly convex in macro-scale,and the interface morphology in micro-scale was irregular,which increased the probability of the nucleation and the formation of the solvent inclusions.Two kinds of PbCl₂ and ZnCl₂ inclusions were found in ZnSe crystals.Most of PbCl₂ inclusions with the homogeneous distribution are much smaller than 50μm and the total concentration is only 7.03×10² cm^-2 in ZnSe single crystals,but ZnCl₂ inclusions with micron-level were only found at grain boundaries.In addition,the formation mechanism of inclusions was discussed by analyzing the microscopic morphology of the growth interface.The evaluations of the crystalline quality of the as-grown ZnSe single crystals were implemented using the chemical etching,X-ray rocking curve,and infrared transmittance measurements.The results indicate that ZnSe single crystals grown by THM have high crystalline quality with the FWHM of 22 arcsec on（220）diffraction planes,the chemical etch pit density of（1-2）×10⁵ cm^-2 on the（110）cleavage plane,and the average infrared transmittance about 70%in the range from 650 cm^-1 to 4000 cm^-1.In addition,the as-grown ZnSe single crystals were annealed and the results showed that the performance of the ZnSe crystals were significantly improved.The infrared transmittance（the ultraviolet transmittance）and the band-gap for ZnSe crystals increased from 30%to 75%,and from 2.56 e V to 2.67 e V,respectively.Further works will focuse on improving the microscopic morphology of the growth interface by optimizing ACRT parameters to reduce or even avoid the solvent inclusions in ZnSe crystals.