Subnanosecond time-resolved emission study of Cu/sub 2/O and GaAs
This thesis presents a series of time-resolved luminescence and light scattering experiments which are aimed at studying how nonequilibrium electron-hole populations excited by picosecond laser pulses in semiconductors reach equilibrium. The development of a time-delayed coincidence photon counting system for the time-dependent measurements is described, and this system is tested by measuring the photoexcited free carrier lifetimes in GaAs doped with deep impurities. The bulk of this thesis is devoted to the study of the dynamics of excitons in Cu/sub 2/O. We first develop a model to explain quantitatively the lineshape of nonthermalized luminescence spectra in Cu/sub 2/O which have been obtained with continuous wave lasers. Then we measure the time-dependence of the ortho-exciton and para-exciton populations in Cu/sub 2/O as a function of temperature. We demonstrate conclusively that the orthoexciton lifetime is dominated by its decay into the para-exciton, and furthermore, this decay rate increases with temperature as T/sup 3/2/. As a result, at low temperatures the ortho-excitons and para-excitons are not in thermal equilibrium, but at T> approx. 40 /sup 0/K the two exciton systems reach thermal equilibrium almost instantaneously. We also studied the time-dependence of both one-phonon and two-phonon Raman modes when resonantly enhanced at the ortho-exciton in Cu/sub 2/O, and found from their time-dependence that these modes should be more correctly identified as hot luminescence. We conclude that time-dependent light scattering and emission measurement is a technique which is capable of greatly improving our knowledge about dynamic processes occurring not only in condensed matter, but, in principle, also in molecular and biological systems. 17 references.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6767667
- Report Number(s):
- LBL-18276; ON: DE85002070
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Thesis
- Country of Publication:
- United States
- Language:
- English
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75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COPPER OXIDES
EXCITONS
OPTICAL PROPERTIES
PHOTOLUMINESCENCE
GALLIUM ARSENIDES
CARRIER LIFETIME
EMISSION SPECTRA
IMPURITIES
LIFETIME
LIGHT SCATTERING
PHONONS
RAMAN EFFECT
ARSENIC COMPOUNDS
ARSENIDES
CHALCOGENIDES
COPPER COMPOUNDS
GALLIUM COMPOUNDS
LUMINESCENCE
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PNICTIDES
QUASI PARTICLES
SCATTERING
SPECTRA
TRANSITION ELEMENT COMPOUNDS
360603* - Materials- Properties
656000 - Condensed Matter Physics