This dissertation focuses on projects where optical techniques were employed to characterize novel materials, developing concepts toward next generation of devices. The materials that I studied included InAsP, InMnSb and InMnAs, and BT-BCN. I have employed several advanced time resolved and magneto-optical techniques to explore unexplored properties of these structures.
The first class of the materials were the ternary alloys InAsP. The electron g-factor of InAsP can be tuned, even allowing for g=0, making InAsP an ideal candidate for quantum communication devices. Furthermore, InAsP shows promises for opto-electronics and spintronics, where the development of devices requires extensive knowledge of carrier and spin dynamics. Thus, I have performed time and polarization resolved pump-probe spectroscopy on InAsP with various compositions. The carrier and spin relaxation time in these structures were observed and demonstrated tunability to the excitation wavelengths, composition and temperature. The sensitivity to these parameters provide several avenues to control carrier and spin dynamics in InAsP alloys.
The second project focused on the ferromagnetic narrow gap semiconductors InMnAs and InMnSb. The incorporation of Mn can lead to ferromagnetic behavior of InMnAs and InMnSb, and enhance the g-factors, making them ideal candidates for spintronics devices. When grown using Molecular Beam Epitaxy (MBE), the Curie temperature (textit{$T_c$}) of these structures is textless 100 K, however structures grown using Metalorganic Vapor phase Epitaxy (MOVPE) have textit{$T_c$} textgreater 300 K. Magnetic circular dichroism was performed on MOVPE grown InMnAs and InMnSb. Comparison of the experimental results with the theoretical calculations provides a direct method to map the band structure, including the temperature dependence of the spin-orbit split-off band to conduction band transition and g-factors, as well as the estimated sp-d electron/hole coupling parameters.
My final project was on the lead-free ferroelectric BT-BCN. Ferroelectric materials are being investigated for high speed, density, nonvolatile and energy efficient memory devices; however, commercial ferroelectric memories typically contain lead, and use a destructive reading method. Reflectometry measurements were used in order to determine the refractive index of BT-BCN with varying thicknesses, which can provide a means to nondestructively read ferroelectric memory through optical methods. / Ph. D. / This dissertation focuses on the characterization of materials that are important for the next generation computer architecture through optical techniques. These materials include the ternary alloy InAsP, the ferromagnetic semiconductors InMnAs and InMnSb, and the lead-free ferroelectric BT-BCN.
InAsP is a ternary alloy composed of the technologically important InAs and InP, and by changing the alloy composition, the band gap and g-factor can be tuned. This allows for InAsP to have band gaps within the communication band, which is important for fiber optic communications as well as infrared photodetectors. As the functionality of these devices depends on the carrier dynamics, I have performed pump-probe spectroscopy in order to probe the carrier and spin relaxation times of this material system. These relaxation times were found to vary with excitation wavelengths, allowing flexibility in the application of this material system for devices.
InAs and InSb are attractive materials for device applications because they offer large electron g-factor, small effective masses, and high mobilities. With the incorporation of Mn, these materials can become ferromagnetic, allowing for their use in ferromagnetic memories as well as other possible devices. The theory of ferromagnetism in semiconductors relies on the interaction between the itinerant holes and the Mn ions, however, in narrow gap semiconductors there is a large band mixing between the conduction and valence band states, and thus the interaction between the conduction band electrons and the Mn is important. In this study, my measurements revealed several interband transitions, which allowed for the calculation of the coupling constants between the electrons, holes and the Mn.
My final study involved the lead-free ferroelectric BT-BCN. Ferroelectric materials are ideal for fast, low power and nonvolatile memories; however, typical implementation utilizes materials that contain lead, and a destructive reading mechanism, requiring a rewrite step. Optical, nondestructive reading methods are being explored based off of the rotation of the polarization of light as it passes through the sample. As this requires knowledge of the refractive index, I performed reflectometry measurements in order to determine the refractive indices of several BT-BCN films.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83494 |
| Date | 15 December 2016 |
| Creators | Meeker, Michael A. |
| Contributors | Physics, Khodaparast, Giti A., Nguyen, Vinh, Scarola, Vito W., Robinson, Hans D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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