The photovoltaic effect was used to study the excitonic transitions in $\rm In\sb{x}Ga\sb{1-x}As/GaAs$ single quantum wells. This work describes at first, the evolution of the exciton observed in photocurrent spectra as a function of the applied electric field. The effect shows a shift of the transition towards longer wavelengths and forbidden transitions ($\rm n \ne n\sp\prime$) are detected. A decrease of the integrated intensity and a broadening of the 11H transition are also observed. Some measurements were taken by simultaneously changing two parameters, the temperature and the electric field. We observed a convolution between the two external influences, a thermal and electric ionization of the excitons that requires a strong electric field at low temperature or a weak field at high temperature. This study then describes the evolution of the 11H exciton (observed in photovoltage and photocurrent spectra) as a function of temperature. The spectra obtained show a large increase of the integrated intensity of the excitonic line between 6K and 87K, and no increase at higher temperature. This is due to the thermal ionization of excitons in the well. In the second chapter, the photovoltaic signal attributed to high density excitons dissociating at a metal-semiconductor interface in a cuprite (Cu$\sb2$O) crystal is measured. The results indicate possible condensation of the excitons and superfluid transport through the three dimensional crystal. The process was repeated for a two dimensional configuration, a $\rm In\sb{x}Ga\sb{1-x}As/GaAs$ single quantum well. We observed a variation in the carrier velocity and intensity as a function of the bi-dimensional excitonic particles density, the sample temperature and the excitation distance. From the results there is no evidence of a phase transition. However, some diffusive transport properties such as the carrier velocity was calculated and compared to previous measurements obtained using different methods.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/6651 |
| Date | January 1994 |
| Creators | Lafrenière, Geneviève. |
| Contributors | Fortin, Emery, |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Detected Language | English |
| Type | Thesis |
| Format | 108 p. |
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