## Band anticrossing effects in highly mismatched semiconductor alloys

Description:
The first five chapters of this thesis focus on studies of band anticrossing (BAC) effects in highly electronegativity- mismatched semiconductor alloys. The concept of bandgap bowing has been used to describe the deviation of the alloy bandgap from a linear interpolation. Bowing parameters as large as 2.5 eV (for ZnSTe) and close to zero (for AlGaAs and ZnSSe) have been observed experimentally. Recent advances in thin film deposition techniques have allowed the growth of semiconductor alloys composed of significantly different constituents with ever- improving crystalline quality (e.g., GaAs{sub 1-x}N{sub x} and GaP{sub 1-x}N{sub x} with x {approx}< 0.05). These alloys exhibit many novel and interesting properties including, in particular, a giant bandgap bowing (bowing parameters > 14 eV). A band anticrossing model has been developed to explain these properties. The model shows that the predominant bowing mechanism in these systems is driven by the anticrossing interaction between the localized level associated with the minority component and the band states of the host. In this thesis I discuss my studies of the BAC effects in these highly mismatched semiconductors. It will be shown that the results of the physically intuitive BAC model can be derived from the Hamiltonian of the many-impurity Anderson model. The band restructuring caused by the BAC interaction is responsible for a series of experimental observations such as a large bandgap reduction, an enhancement of the electron effective mass, and a decrease in the pressure coefficient of the fundamental gap energy. Results of further experimental investigations of the optical properties of quantum wells based on these materials will be also presented. It will be shown that the BAC interaction occurs not only between localized states and conduction band states at the Brillouin zone center, but also exists over all of k-space. Finally, taking ZnSTe and ZnSeTe as examples, ...

Date:
September 9, 2002

Creator:
Wu, Junqiao

Partner:
UNT Libraries Government Documents Department