Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor

Gregory Salamo

Committee Member

Surendra Singh

Second Committee Member

Laurent Bellaiche

Third Committee Member

Shui-Qing Yu

Fourth Committee Member

Salvador Barraza-Lopez

Keywords

Nonlinear-optics, Photoluminescence, Quantum Dots

Abstract

Semiconductor quantum dots (QDs) confine carriers in three dimensions, resulting in atomic-like energy levels as well as size-dependent electrical and optical properties. Self-assembled III-V QD is one of the most studied semiconductor QDs thanks to their well-established fabrication techniques and versatile optical properties. This dissertation presents the photoluminescence (PL) study of the InAs/GaAs QDs with both above bandgap continuous-wave excitation (one-photon excitation) and below-bandgap pulse excitation (two-photon excitation). Samples of ensemble QDs, single QD (SQD), and QDs in a micro-cavity, all grown by molecular beam epitaxy, are used in this study. Morphology of these samples was examined using atomic force microscope and transmission electron microscope. Two-photon excitation uses energy near half of the QDs ground state transition, all the way up to half of the GaAs matrix bandgap. Power dependent QDs PL with both one-photon and two-photon excitation can be described by power laws, with power index of 1 for one-photon excitation and two for two-photon excitation. Photoluminescence excitation spectroscopy then provides evidence of direct two-photon absorption into the QDs when the two-photon excitation energy is resonant with the QDs state. For SQD without cavity, we observed PL of a SQD with excitation near its half bandgap. The QDs in a micro-cavity sample consists one layer of InAs QDs in a GaAs spacer sandwiched between two distributed Bragg reflectors made of alternating layers of GaAs and AlAs. We successfully observed PL from SQD emitted from the cavity mode with excitation slightly above half of the QD’s transition. These observations help us to understand the nonlinear optical property of InAs QDs and can be potentially used in all-optical computation or reflective optical limiters.

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