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Confined States in GaAs-based Semiconducting Nanowires

Shi, Teng
http://orcid.org/0000-0002-7919-3831
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1460447182

Abstract Details

2016, PhD, University of Cincinnati, Arts and Sciences: Physics.
In this dissertation, a wide variety of optical spectroscopies including photoluminescence (PL), photoluminescence excitation (PLE), photoluminescence imaging, time-resolved photoluminescence (TRPL), as well as photocurrent (PC) spectroscopy have been used to explore the optical and electronic structures of Zn-doped GaAs twinning superlattices (TSL) and GaAs/AlGaAs quantum well tube (QWT) nanowires. Low Temperature PL spectra of a single Zn-doped GaAs TSL nanowire reveal a broad band low energy emission centerd at 1.47 eV in addition to the free exciton emission of zincblende GaAs. We do not observe any changes in the relative ratio of these emissions as a function of excitation power, suggesting that the low energy emission is not related to defects or carbon impurities, this is further confirmed by PC measurement. A simple theoretical model with holes confined in the wurtzite segment is developed in order to understand the origin of the emissions. In GaAs/AlGaAs QWT nanowires, low temperature PL spectra of 8 and 4 nm QWTs show that the exciton confinement energy have been shifted up by 57 meV and 185 meV with respect to the GaAs core. A first excited state transition has been observed in PLE spectra of only the 8 nm QWT. A simple theoretical modeling using a cylindrical quantum well shows the calculations are in good agreement with both direct and indirect transitions observed in PL and PLE measurements. A more detailed model including the hexagonal symmetric facets shows that the electron and holes ground states are strongly localized to the corners, while the excited states are confined to the long facets of the QWT. In order to gain more information about quantum confined energy in these radial heterostructures, we then studied a series of QWTs with thicknesses ranging from 1.5 to 8 nm. High resolution spatially-resolved PL images reveal several ultranarrow emission lines (localized states) distributed at different spatial positions along the long axis of 2 and 4 nm QWTs, but no such localized states are observed in the 6 and 8 nm QWT nanowires. This indicates that narrow QWTs are more sensitive to well width and alloy fluctuations. In the 2 nm QWT, high resolution PL spectra reveal many ultranarrow emission lines on the high energy side at low temperatures. These localized states quench rapidly compared to the low energy emissions as a function of temperature. The overall emission linewidth also decreases as a function of temperature. Time-dependent PL spectra show that the localized states are stable at low temperatures but become metastable at higher temperature. We developed a rate equation model where localized states are decoupled with the delocalized states at low temperatures, but become strongly coupled once the excitons have enough thermal energy to surmount the energy barrier at higher temperature. Parameters extracted from this model show a thermal activation energy of 10.9 meV for the localized states. The model provides a view of the evolution of the complex energy landscape in these QWTs as a function of temperature from 10 to 120 K.
Leigh Smith, Ph.D. (Committee Chair)
Howard Everett Jackson, Ph.D. (Committee Member)
Randy Johnson, Ph.D. (Committee Member)
Nayana Shah, Ph.D. (Committee Member)
138 p.
Condensation
nanowire; quantum confinement; excitation spectroscopy; heterostructures; quantum dots

Recommended Citations

Citations

  • Shi, T. (2016). Confined States in GaAs-based Semiconducting Nanowires [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1460447182

    APA Style (7th edition)

  • Shi, Teng. Confined States in GaAs-based Semiconducting Nanowires. 2016. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1460447182.

    MLA Style (8th edition)

  • Shi, Teng. "Confined States in GaAs-based Semiconducting Nanowires." Doctoral dissertation, University of Cincinnati, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1460447182

    Chicago Manual of Style (17th edition)

ucin1460447182
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This open access ETD is published by University of Cincinnati and OhioLINK.