Magnetic Field induced Metal Nonmetal Transition for Semiconductors by Use of Zeeman Magneto-Spectroscopy

为了用塞曼磁谱研究半导体的磁场诱导金属-非金属相变，我们采用了导带有效质量各向同性的n-GaAs，它符合有效质量近似。N-GaAs金属-非金属转变的临界施主浓度为1.6×10~(-3)cm~(-3)。我们已经制备了10多种外延生长的n-GaAs样品，其浓度在10^&lt；14-gt；-3-gt；和10^-lt；18-gt；-3&gt；-3之间。详细研究了施主浓度、磁场和温度对ls*2P&lt；+1&gt；相变施主的塞曼磁吸收的影响。当可以观察到塞曼磁吸收时，半导体处于非金属相，反之亦然。我们观察到，随着施主浓度的增加，塞曼磁吸收谱线明显展宽，超过临界施主浓度后，塞曼吸收谱线消失。此外，我们还观察到随着磁场的增加，塞曼吸光系数显著变窄。在磁场的应用中，人们认识到临界施主浓度向更高的浓度移动，以及磁场诱导的金属-非金属相变。为了定量地解释我们的实验结果，我们在Thomas-Fermi近似下进行了变分计算，并计算了金属-非金属转变的临界施主浓度。利用可靠的变分波函数，首次计算了磁场中施主的能级，得到了较好的结果。其次，我们进行了屏蔽的数值计算，第三，我们将计算扩展到了磁场和屏蔽存在的情况。

To study the magnetic field induced metal-nonmetal transition for semiconductors by use of Zeeman magneto-spectroscopy, we have employed n-GaAs, which has a isotropic effective mass of the conduction band and can be fitted to the effective mass approximation. The critical donor concentration of the metal-nonmetal transition for n-GaAs is 1.6*10^<16>cm^<-3>. We have prepared more than 10 kinds of epitaxially grown n-GaAs samples of which concentration is between 10^<14>cm^<-3> and 10^<18>cm^<-3>. Zeeman magneto-absorption of donors for ls*2P_<+1> transition has been investigated in details as the functions of donor concentration, magnetic field and temperature. When the Zeeman magneto-absorption can be observed, the semiconductor is in the nonmetallic phase, and vice versa. We have observed the striking line-broadening of the Zeeman magneto-absorption with increasing the donor concentration and the disappearance of that above the critical donor concentration. Furthermore, we have observed the considerable narrowing of the Zeeman magneto-absorption with increasing the magnetic field. The shift of the critical donor concentration to a higher one and the magnetic field induced metal-nonmetal transition have been recognized on the application of the magnetic field. To explain our experimental results quantitatively, we carried out variational calculations within the Thomas-Fermi approximation and evaluated the critical donor concentration of the metal-nonmetal transition. Employing the reliable variational wavefunctions, we firstly calculated energy levels of a donor in a magnetic field without the screening and obtained the good results. We secondly carried out numerical calculations with screening and thirdly extended our calculations to the case in the presence of the magnetic field and the screening.