J.M. Shi

Magneto-polaron effect on shallow donors in bulk GaAs and on D0 and D− in GaAs/AlGaAs superlattices

Abstract A theoretical study is made of the energy levels of shallow donors in bulk GaAs and in GaAs/AlGaAs superlattices in an external magnetic field. The influence of magneto-polarons on these energy levels is studied within second-order perturbation theory. Special attention is paid to the resonant polaron interaction, and the importance of band non-parabolicity at high magnetic fields is also shown. Once-electron as well as two-electron bound states of the donor are investigated. Our results are in good agreement with available experimental far-infrared optical data of the different transitions within the above systems.

Transition energies of D- centers in a superlattice

Abstract We study a negative-donor center (D − ) in a GaAs/AlGaAs superlattice in high magnetic fields along the growth axis. The energy levels of the D − states are calculated by a variational approach using a trial wave function which (1) includes electron-electron (e−e) correlation for the superlattice case, (2) with, and (3) without c-e correlation for the situation of a quantum well (QW). Polaron effects arc included within second-order perturbation theory. A detailed comparison is made of the calculated transition and binding energies with the measured data of Huant et al. [4]. We found that these experimental results should be interpreted as the transition energy between two D − states.

Polaron correction to the D− center in a quantum well

Abstract A theoretical study is presented of the negative-donor center (D−) in a quantum well (QW) in a magnetic field. The energy levels of a spin singlet state (s-like), and spin triplet states (pt±-like) of the D− center are calculated by a variational approach. The polaron correction to the D− states is discussed within second-order perturbation theory in which only the three-dimensional (3D) bulk phonon modes of GaAs are invoked. We find that the polaron correction is very important in order to explain the experimental results.

Magnetopolaron effect on shallow donors in bulk and in weakly and strongly coupled superlattices

Impurity bound magneto-polarons are studied in bulk and in weakly and strongly-coupled GaAs/AlGaAs superlattices. A variational approach is used to calculate the energy levels of several donor states as function of: (1) the well width, (2) the donor position, and (3) the magnetic field strength. The tunneling of the electron in the adjacent wells of the superlattice is incorporated in our calculation. The 1s → 2p+ transition of shallow donors is tuned through resonance with the GaAs optical phonon mode. The theoretical analysis shows that: (1) the size of the magneto-polaron effects is very close to those for the bulk system, and (2) no direct evidence is found for non bulk LO-phonon interaction.

Magneto-Polaron Effect on Shallow Donors in 3D and Q2D Systems

An overview is given of the energy levels of shallow donor states in a three-dimensional and in a quasi-two-dimensional system in a magnetic field. We apply our results to bulk GaAs, and to GaAs/AlGaAs quantum wells or superlattices. For the quantum well case we also study the negativedonor center. The importance of the polaron effect and band nonparabolicity is shown. Our theoretical results are in good agreement with available experimental data.

Magneto-Optics of Shallow Impurities in Superlattices

The ground and excited states of shallow impurities in quantum wells and superlattices in the presence of a magnetic field along the growth axis are studied. We discuss the neutral D°-center and the charged D”-center. The importance of electron-phonon interaction and band non-parabolicity in realistic systems is pointed out. The theoretical results are compared with recent experimental data on the GaAs/AlxGa1-xAs system.