Precise measurement of diffusion coefficient in semiconductor melt under strong magnetic field

本文利用强静态磁场对半导体熔体在熔点至1500 K范围内的扩散系数进行了精确测量，并将测量数据与微重力环境下的测量数据和硬球模型的估定值进行了比较。通过基于精细元法的数值模拟，推导了静态磁场中扩散实验的一些实验条件。在此基础上，利用图像炉进行了in - sn、ga掺杂Ge、Ge- si和In_*Ga_<1*>As熔体在静态磁场中的扩散实验。得到的扩散系数结果如下：1。在熔点附近得到的系数与硬球模型的估算值吻合较好，但高温下实验值的温度依赖性与空间实验结果几乎相同。对于所谓“简单液体”中扩散过程的物理模型，应根据在较高温度下得到的实验数据进行修正。掺ga的Ge和Ge- si：得到的系数比硬球模型估计的要高得多。结果支持了Itami模型的有效性，该模型假设熔融Ge具有分子间弱共价键的结构。In_*Ga_<1*>As：由于伪二元相图中模具偏析系数较大，导致溶质种偏析，本方法没有得到可靠的数据。在大偏析系数合金中，应用强静磁场的剪切单元法是提高实验数据可靠性的一种有效方法。

In the present study, diffusion coefficients in semiconductor melt were measured precisely by utilization of a strong static magnetic field from the melting point of the specimen to 1500 K and then the measured data were compared with those obtained in the microgravity environment and with the estimated values by a hard sphere model.Some experimental conditions for diffusion experiment in a static magnetic field were derived by a numerical simulation based of a fine element method. Based on the numerical result, the diffusion experiments for In-Sn, Ga-doped Ge, Ge-Si and In_*Ga_<1*>As melts were performed using an image furnace in a static magnetic field. The obtained results for the inter-diffusion coefficients were as follows.1. InSn : The obtained coefficients near the melting point agreed well with those estimated by a hard sphere model However, the temperature dependency of the experimental values at high temperature was almost same as the space experiment result. The physical model for diffusion process in a so-called "simple liquid" should be modified based on the experimental data obtained in higher temperature.2. Ga-doped Ge and Ge-Si : The obtained coefficients were much higher than those estimated by the hard sphere model. The results supports validity of the Itami's model which assumes molten Ge has a structure with a weak covalent bonding between the molecules.3. In_*Ga_<1*>As : No reliable data was obtained by the present method due to the segregation of the solute species, because die segregation coefficient was large in the pseude-binary phase diagram. A shear cell method with an application of strong static magnetic field is a promising way to improve reliability of the experimental data in the case of alloy with a large segregation coefficient.