采用热力学数值计算的方法,分析了ZnSe-12、H2、HC1和NH4Cl化学气相输运系统的特性.对比计算结果表明,ZnSe-NH4Cl系统具有压力高、输运反应焓变适中的特点.NH3分解产生的H2起着调节输运组分H2Se分压的作用.以ZnSe—12输运系统中实际输运组分分压值为参考,确定了ZnSe—NHaCl系统中单晶生长工艺参数范围:温度在1000℃左右,NH4C1的浓度范围在0.5—1.0mg/mL之内.采用该工艺生长了尺寸约为8ram×6mm×4mm的ZnSe单晶,生长态(111)面摇摆曲线半峰宽为60.48",蚀坑密度(EPD)为(4.5-5.O)×10^4/cm^2.
The thermodynamic properties of transporting reactions in ZnSe-I2, -H2, -HCl and -NH4Cl chemical vapor transport systems were analyzed by solving sets of equations with numerical methods. The results show that ZnSe-NH4Cl system has the properties of high total pressure and moderate reaction enthalpy change. The hydrogen (H2) produced through decomposition of NH3 is capable to adjust the transporting component partial pressure of H2Se. Referring to the component partial pressure in ZnSe-I2 system, the process parameters in ZnSe-NH4Cl system are primarily selected for ZnSe single crystal growth. The concentration of NH4Cl ranges from 0.5 to 1.0mg/mL at the growth temperature of about 1000℃. An as-grown ZnSe single crystal is obtained with dimension of 8mm×6mm×4mm. The full width at half maximum of X-ray double crystals rocking curve on (111) as-grown surface is 60.48" and the etching pits density (EPD) is about (4.5-5.0)× 10^4/cm^2.