Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Physics

Committee Chair(s)

David M. Riffe

Committee

David M. Riffe

Committee

Eric D. Held

Committee

David Peak

Committee

Shane Larson

Committee

Steve Bialkowski

Abstract

In semiconductors, everything is becoming smaller day by day; quantum dots are the smallest nanomaterials available today. Typical sizes of these quantum dots are in the range of 5 to 30 nm in diameter. Variations in size changes many material properties, such as electrical and nonlinear optical properties, making them very different from bulk semiconductors. The size of the QDs results in new quantum phenomena, which yield some extraordinary properties. Material properties change dramatically because quantum effects arise from the confinement of electrons and holes in the material. Hence, semiconductor quantum dots play an important role in designing new devices and technologies. To make new devices, the study of carriers (electrons and holes) in quantum dots plays a significant role.

Ultrafast spectroscopy has been used to study the carrier dynamics in quantum dots. Ultrafast spectroscopy was revolutionized in the 1980s by the invention of 100-fs (fs = 10−15sec) pulses. In early 1990 a new revolution came in the field of lasers that produced ultra short pulses using Ti-sapphire oscillators. With these new Ti-sapphire lasers, one can produce laser pulses of 4-5 fs duration. These diode-pumped, solid-state lasers quickly replaced the expensive, large, and low-efficiency ion lasers. Ultrafast lasers can also be used to produce laser pulses with enormous peak power. In our lab, we produce 28-fs laser pulses with 1 nJ of energy. Each ultra-short pulse carriers power of 36 KW in our lab. The ultra-short pulse allows one to create, detect, and study very fast relaxation in semiconductors. The use of ultra-short pulses has opened the door to many new findings in fundamental semiconductor mechanisms, especially those concerning carrier dynamics.

In this dissertation, we study carrier dynamics in quantum dots. Using the reflectivity experiment, we found capture times of electrons, i.e., how much time an electron takes to reach the quantum dot layer, and we have also measured relaxation times for carriers (when electron and hole relaxes) with the QDs.

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This work made publicly available electronically on 2/2013

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