| Summary: | 博士 === 國立臺灣大學 === 物理研究所 === 100 === In this dissertation, we mainly focus on the study of the physical properties of ZnO nanostructures, InGaN/GaN multiple quantum wells, and their composites. Based on the discovered novel properties, we attempt to develop their potential applications. A brief description of our main findings has been summarized as follows. It is believed that our results shown here should be very useful for the general interests both in academics as well as industry
1. Tunable Photoluminescence and Photoconductivity in ZnO One-dimensional Nanostructures with a Second Below-gap Beam
Tunable photoluminescence (PL) and photoconductivity (PC) with a second below-gap beam were demonstrated on ZnO nanorods and nanoribbons. We found that both PL and PC could be quenched as the second beam was applied on the nanostructures, and this behavior was excluded from thermal effect by comparing the phonon replica spectra with that of heating the sample directly. The most quenching effect occurred near the defect transition locating at 520 nm. The underlying mechanism of the quenching behavior was attributed to the defect transition between different states of oxygen vacancies. Size-dependence measurement lets us know the effect occurs near the surface of nanostructures, and the power-dependent measurement further confirms the underlying mechanism we proposed.
2. Symmetrically Tunable Optical Properties of InGaN/GaN Multiple Quantum Disks by an External Stress
The influence of an external stress on the optical properties of InGaN/GaN multiple quantum disks (MQDs) has been investigated. As a transversal force is applied on the MQDs, both photoluminescence and Raman scattering spectra are altered due to the piezoelectric potential accompanied by the quantum confined Stark effect. Quite interestingly, it is found that the optical spectra possess a sixfold symmetry about the c-axis. This intriguing phenomenon can be attributed to the inherent nature of hexagonal lattice as well as the good flexibility of the composite consisting of polydimethylsiloxane and MQDs. Our results can provide an alternative route to optimize and extend the application of nitride-based devices.
3. Light-emitting Devices with Tunable Color from ZnO Nanorods Grown on InGaN/GaN Multiple Quantum Wells
Based on the composite consisting of ZnO nanorods (NRs) grown on InGaN/GaN multiple quantum wells (MQWs), we have demonstrated a novel light-emitting device (LED) that has the capability to emit dual beam radiations. Interestingly, the relative intensity between the dual emissions is able to be manipulated by their polarizations. The underlying mechanism can be well understood in terms of the anisotropic optical properties arising from the geometric structures of constituent nanoscale materials. The results shown here may be extended to many other nanocomposite systems and pave a new pathway to create LEDs with tunable properties.
4. Optical Detection of Glucose Based on the Composite Consisting of Enzymatic ZnO Nanorods and InGaN/GaN Multiple Quantum Wells
Based upon the high surface-to-volume ratio of nanorods and high sensitivity of piezoelectric properties of nitride semiconductors, enzymatic functionalized composite consisting of nanorods and nitride light emitting devices (LEDs) provide an excellent opportunity for the development of glucose detectors using optical methods. To demonstrate our working principle, a sensing device based on InGaN/GaN multiple quantum wells and ZnO nanorods has been constructed and exposed to target glucose solutions. The pronounced changes of emission as well as Raman scattering spectra under different target glucose concentrations clearly illustrate the feasibility of our newly designed composite for the creation of highly sensitive biosensors with optical detection.
5. Optical Detection of Hydrogen Gas Using Pt-catalyzed ZnO Nanorods and InGaN/GaN Multiple Quantum Wells
Based upon the high surface-to-volume ratio of nanorods and high sensitivity of piezoelectric properties of nitride semiconductors, catalyst decorated composite consisting of nanorods and nitride light-emitting devices (LEDs) provide an excellent opportunity for the development of gas detectors using optical methods. To demonstrate our working principle, a sensing device based on the composite consisting of InGaN/GaN multiple quantum wells (MQWs) and Pt-catalyzed ZnO nanorods has been fabricated and exposed to target hydrogen gas. The pronounced changes of emission as well as Raman scattering spectra of InGaN/GaN MQWs under different target gas concentrations clearly illustrate the feasibility of our newly designed composites for the creation of highly sensitive gas sensors with optical detection.
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