Dissertations, Theses, and Capstone Projects

Date of Degree

9-2017

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Maria C. Tamargo

Committee Members

Aidong Shen

Igor L. Kuskovsky

Glen Kowach

Subject Categories

Materials Chemistry

Keywords

Quantum Cascade Detectors, Quantum Cascade Lasers, Superlattices, Virtual Substrates, Molecular Beam Epitaxy, Topological Insulators

Abstract

Molecular Beam Epitaxy(MBE) is a versatile thin film growth technique with monolayer control of crystallization. The flexibility and precision afforded by the technique allows for unique control of interfaces and electronic structure of the films grown. This facilitates the realization of novel devices and structures within a research environment normally only achieved though complex industrial processes. In the past, the control of each interface in MBE has been explored to great benefit. In this work, we study the control of these interfaces so as to increase the performance of novel devices material systems. This dissertation focuses on two main areas in which to manipulate interfaces for our benefit: II-VI Intersuband(ISB) devices and II-VI/Bi2Se3 heterostructures.

Intersuband(ISB) devices, such as quantum cascade(QC) lasers and QC detectors operating in the infrared range, were first realized with this technique. ISB devices offer critical advantages over interband devices especially in the infrared and terahertz range. ISB devices present extremely flexible parameter space for design as they are based on thicknesses of quantum wells(QWs) rather than intrinsic properties of the materials. QC lasers II-VI materials support shorter wavelengths in the infrared than do commercially available III-V materials. ZnCdSe/ZnCdMgSe lattice matched to InP allows for QC laser designs to reach up to 2µm due to a conduction band offset of 1.12eV. Also, the relatively high effective mass and the before mentioned conduction band offset make them attractive for QC detectors. Our research demonstrates that with the use of interface control, novel high performance detectors can be achieved within this material system. Additionally, we consider the future of this material system by exploring MgSe/ZnCdSe short period superlattices as a plausible replacement for ZnCdMgSe in these types of devices.

Topological insulators, a new class of materials, have recently attracted a great deal of attention in the scientific community. Among these, Bi2Se3 has a near ideal Dirac cone at the Γ point. Here we demonstrate this material in heterostructures with II-VI semiconductors in order to set the foundation for a new material system for both physical and possible device applications. We also investigate using Bi2Se3 as a virtual substrate for II-VI materials.

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