We have developed a variational formalism to calculate the effects of electric and magnetic fields on confined hydrogenic donor states in asymmetric coupled double quantum well structures. It is demonstrated that an electric field applied along the growth axis can easily shift the electron wave function from one quantum well across the center barrier into the neighboring well, without ejecting the electron from a confined donor state. Depending on donor location in the structure, binding energy can either increase or decrease under the applied electric field, as had been found in the case of single quantum wells, but with significantly greater rates of change in response to the external field. The magnetic field applied along the growth axis of the quantum well structure leads to additional quantum confinement, increasing both the donor binding energies and the transition energy between the 1s and 2p + donor states. Effect of the relative size of the two coupled quantum wells on the donor binding energy is also discussed. Dipole moment and polarizability of the confined donor states are obtained simultaneously as well.
[Show abstract][Hide abstract] ABSTRACT: This is the final technical report for University Research Initiative (URI) program 'Spatial Light Modulators with Arbitrary Quantum Well Profiles. This program explored the use of quantum wells having arbitrary shapes for optical modulators and lasers. This comprehensive effort addressed MBE growth of compositionally graded wells and dielectric mirrors, accurate measurements of absorption coefficient in free-standing membranes, comparison of different active region optical properties, device fabrication and theory of excitons in the presence of applied electric and magnetic fields.
[Show abstract][Hide abstract] ABSTRACT: We have developed a variational formalism for the calculation of the binding energies of hydrogenic donors in the so-called ``dielectric quantum wells,'' where the dielectric constant of the barrier material is significantly smaller than that of the well material, in the presence of magnetic and electric fields applied along the growth axis. We derive an expression for the anisotropic electron-donor-ion interaction potential analytically by solving the Poisson equation in the layered geometry of quantum-well structures. Binding energies of the 1s and 2p states are then calculated using the Gaussian-type orbital expansion method. Effects of the applied electric field, magnetic field, and the interfacial dielectric-constant mismatch on the binding energies of donor states are studied in detail.
[Show abstract][Hide abstract] ABSTRACT: We study the effect of a magnetic field applied along the growth axis on exciton binding energies in dielectric quantum-well structures, in which the dielectric constant of the confining barriers is significantly smaller than that of the well material. The anisotropic electron-hole Coulomb interaction potential is obtained analytically by solving the Poisson equation in the layered geometry of quantum wells. Confinement is provided by the image charge distribution arising from the mismatch of dielectric constants at the interfaces, in addition to that of the quantum-well potential and the applied magnetic field. Exciton binding energies are calculated using the Gaussian-type orbital expansion method. Significantly enhanced binding energies are obtained for the excitons in various dielectric quantum-well structures and their behavior in a magnetic field is discussed.
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