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采用专业的晶体生长模拟软件CGSim模拟了垂直梯度凝固法(VGF)GaAs单晶生长过程中固液界面形状及其变化;分析了生长过程中界面上不同位置的热通量及其变化,并利用能量守恒关系,分析了热通量对固液界面形状的影响,改进了前人在忽略凝固或熔化相变潜热的基础上推导出的固液界面形状和温度梯度之间的数学关系。结果表明:固液界面上各点热通量的不同导致各点生长速度的不同,从而形成偏离程度各异的固液界面形状。采用霍尔效应测量法检测了GaAs单晶中的载流子浓度分布,分析了固液界面形状对晶片电学均匀性的影响。结果表明:对于分凝系数k0<1的溶质,平坦的固液界面,晶片中载流子浓度分布更为均匀;凸形界面,载流子浓度随晶片径向距离的增加而增加;凹形界面,载流子浓度随晶片径向距离的增加而降低;载流子浓度分布的不均匀性随固液界面非平坦性的增加而增加。
The shape and the change of solid-liquid interface in vertical gradient solidification (VGF) GaAs single crystal growth were simulated by a professional crystal growth simulation software CGSim. The heat flux and its change at different positions on the interface during growth were analyzed. The relationship between the heat flux and the shape of the solid-liquid interface is analyzed, and the mathematical relationship between the solid-liquid interface shape and the temperature gradient derived from the ignorance of the latent heat of solidification or melting is improved. The results show that the different heat flux at each point of the solid-liquid interface leads to different growth rates of each point, resulting in different solid-liquid interface shapes. The carrier concentration distribution in GaAs single crystal was measured by Hall effect measurement, and the influence of solid-liquid interface shape on the electrical uniformity of the wafer was analyzed. The results show that for the solute with the segregation coefficient k0 <1, the carrier concentration in the wafer is more uniform at the flat solid-liquid interface; the carrier concentration at the convex interface increases with the increase of the radial distance of the wafer; At the interface, the carrier concentration decreases with the increase of the radial distance of the wafer. The nonuniformity of the carrier concentration distribution increases with the increase of the non-flatness of the solid-liquid interface.