Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Iyer, Shanthi

Abstract

Infrared (IR) sensors are extremely important in missile defense as well as in satellite-based infrared detection systems. Long-range ballistic missile defense for incoming missile acquisition, tracking, and discrimination requires space-based infrared technology. Hence long wavelength and very long wavelength infrared regimes are extremely important for such applications. The focus of this work is on the investigation of superlattices (SLs) and in particular dilute nitride based SLs for such applications in this infrared region. A comprehensive study of InAs/GaSb, InAs/GaInSb, InAsN/GaSb and InAsN/GaInSb SLs grown by molecular beam epitaxy (MBE) has been carried out using different characterization techniques. Optimization of the structures with growth parameters such as interfacial layers, layer thickness, and material composition will also be discussed. The judicious selection of the above combination of parameters was abetted by theoretical simulation using OPTEL_ZB software. A systematic and detailed study has been made correlating the structural quality, vibrational modes, scanning transmission electron microscope (STEM) micrographs and optical properties of each of the optimized structure of the SL. All the SLs were defect free with sharp interfaces and well defined sublayers as attested by high resolution x-ray diffraction (HRXRD) and asymmetric reciprocal space mapping (RSM) spectra as well as STEM images. The unique feature of this work is the growth of InAsN/GaSb SL which has not been reported elsewhere to the best of our knowledge. This SL shows promise in that thinner layers of InAsN were used for the same strain balancing effect as thicker InAs. Hence the former would improve optical absorption. Since the N in InAsN reduces the overall lattice constant of the material system it added another degree of freedom in strain balancing the structure to the GaSb substrate. A cut off wavelength of ~20 μm was achieved with the InAsN/GaSb SL.

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