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

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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.