Metal-insulator transitions due to shallow donors in a GaAs/AlGaAs quantum well

Some of the excited states of a hydrogenic donor in a quantum well formed by GaAs and Ga1−xAlxAs are calculated for various well widths and different concentrations. Metal-Insulator transition in a doped semiconductor is investigated using the Lindhard dielectric screening function and screened Coulomb potential in the Hamiltonian. The effect of correlation among electrons is considered through effective mass, which depends on the spatial separation between impurities. The diamagnetic susceptibility of a hydrogenic donor impurity in a GaAs/Ga1−xAlxAs quantum well system is found out in the observation of metal-insulator transition. We believe such investigation of χdia of the donor in a QW will be relevant to the interpretation of semiconductor-metal transition in low-dimensional semiconductor systems. It is shown that the diamagnetic susceptibility diverges for all critical concentration for a given well width. The results show that the occurrence of 1s-2pz impurity transitions is a useful tool to investigate the electronic properties near the metal-insulator transition. These measurements indicate that in spite of metallic behaviour, the transition occurs in the impurity band itself, which has not merged with the conduction band. The results are compared with the existing data available and discussed in the light of the existing literature.