Localization of excitons in an indirect gap GaAs/AlAs superlattice

Thesis/Dissertation · Thu Dec 31 23:00:00 EST 1992

OSTI ID:7280240

Angell, J F

This thesis develops in chapter 2 a theory based on a model of exciton mobility in which, as temperature is increased, excitons gain thermal energy and begin to jump from site to site. This jumping allows them to motionally average the distribution of decay rates. The theory has one fitting parameter, [gamma], which is the ratio of excitons lifetime to jump time and determines the extent of averaging performed. The mathematical formalism used to develop this theory is identical to that used by E. Jakeman and E.R. Pike (1968) in calculating the intensity distribution of Gaussian light. This is, however, the first time that this method of statistical averaging has been applied to excitons in a disordered medium. In chapter 4 the theory is compared with new intensity decay measurements performed on type II GaAs/AlAs superlattices made at different exciton energies and different excitation intensities. Good agreement is found between the theory and experimental data, however it is found that at high excitation intensity and low exciton energy there is an apparent saturation of localized states, and the theory must be modified under these conditions to include a population of excitons which are delocalized even at low temperature. The fitting parameter, [gamma], is found to increase with temperature according to two thermally activated processes. One of these has a low activation energy and is interpreted as the localization energy, and the other has a higher activation energy and is interpreted as the exciton binding energy. Both activation energies are in reasonable agreement with previously reported results, however there is no evidence of a mobility edge.

• Research Organization: Dartmouth Coll., Hanover, NH (United States)
• OSTI ID: 7280240
• Country of Publication: United States
• Language: English

Related Subjects

664200* -- Spectra of Atoms & Molecules & their Interactions with Photons-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ALUMINIUM ARSENIDES
ALUMINIUM COMPOUNDS
ARSENIC COMPOUNDS
ARSENIDES
EXCITONS
FUNCTIONS
GALLIUM ARSENIDES
GALLIUM COMPOUNDS
GAUSS FUNCTION
LUMINESCENCE
MATERIALS
MATRICES
PNICTIDES
QUASI PARTICLES
S MATRIX
SEMICONDUCTOR MATERIALS
SUPERLATTICES