Optical Studies and Applications of Single Quantum Dots

University dissertation from Solid State Physics, Lund University, Box 118, SE-22100 Lund, Sweden

Abstract: The luminescence from single quantum dots has been studied. Single dot photoluminescence was studied under continuous as well as under pulsed excitation. Time-resolved studies revealed fast relaxations in quantum dots. The time resolved measurements were fitted with a set of rate equations. Blinking in the luminescence was observed on a few quantum dots. The polarization of the emission from single quantum dots was also measured. The emission correlation was measured on a single dot and revealed the antibunched nature of the emission from single quantum dots. Single photon generation on demand was demonstrated with a single quantum dot under pulsed excitation. Attempts to generate entangled photon pairs with a single quantum dot were also made. Devices containing single quantum dots as the active region were fabricated. Light Emitting diodes were fabricated and studied, the electroluminescence from single quantum dots has been observed. Two types of microcavities containing single dots were also fabricated, planar microcavities where the light is confined between two planar mirrors and microdisks, where the light is confined in a high refractive index disk-shaped cavity in whispering modes. A processing technique was developed to position selected single quantum dots in microdisks with submicron resolution to achieve maximum coupling with the whispering modes. The problem of the very limited light extraction efficiency from high refractive index materials was studied and solid immersion lenses were used to increase the light extraction efficiency from single quantum dots. Theoretical calculations gave results in good agreement with experimental observations. Further improvements to solid immersion lenses were also studied.

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