Novel physical properties induced by nanostructured semiconductors, photonic crystals, surface plasmons, and magnetic materials
| Autor: | Chih-Ming Wei, 魏志銘 |
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| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 99 In this dissertation, we have reported the novel physical properties in the composites consisting of nanostructured semiconductors, photonic crystals (PCs), surface plasmons, and magnetic materials. The results can be divided into four parts which are spin transport in Si0.5Ge0.5/Si multiple quantum wells (MQWs), enhancement of luminescence extraction in Si0.5Ge0.5/Si MQWs by using PCs, manipulation of localized surface plasmon resonance (LSPR) by applying magnetic fields, and magnetoelectric (ME) effect in the composite consisting of piezoelectric semiconductors and ferromagnetic materials. In the first part, we have studied the properties of spin transport in Si0.5Ge0.5/Si MQWs. Circular photogalvanic effect (CPGE) and linear photogalvanic effect for interband transition have been observed simultaneously in Si0.5Ge0.5/Si MQWs. The signature of the CPGE is evidenced by the change of its sign upon reversing the radiation helicity. It is found that the observed CPGE photocurrent is an order of magnitude greater than that obtained for intersubband transition. The dependences of the CPGE on the angle of incidence and the excitation intensities can be well interpreted based on its characteristics. The large signal of spin generation observed here at room temperature should be very useful for the realization of practical application of spintronics. In the second part, we have successfully achieved the selective enhancement and suppression of the photoluminescence (PL) arising from Si0.5Ge0.5/Si MQWs by PCs. The formation of the stop band in PCs is designed to be a filter as well as a reflector. It is found that the self-assembled PCs are able to selectively enhance the luminescence of the type-II transitions at the interface between Si and Si0.5Ge0.5/Si layers and suppress the emission from Si. Our working principle shown here can be extended to many other material systems, and should be very useful for creating high power solid-state emitters. In the third part, magnetically tunable LSPR based on the composite consisting of noble metal nanoparticles and a ferromagnetic thin film have been demonstrated. It is found that both of the frequency and linewidth of the LSPR can be manipulated by applying an external magnetic field. The underlying mechanism is attributed to the variation of the dielectric constant in the ferromagnetic thin film resulted from the change of the magnetization. Our result shown here paves an alternative route to manipulate the characteristics of LSPR, which may be served as a new design concept for the development of magneto-optical devices. In the final part, The ME effect has been demonstrated based on the composite of the InGaN/GaN MQWs and the FeCo thin film. By applying an external magnetic field, the ferromagnetic layer will be deformed due to magnetostriction. This deformation is transmitted to the piezoelectric layers and results in piezoelectric effect, which induces electric polarization in the piezoelectric layers. The induced electric polarization changes the strain and the built-in internal electric field in the InGaN/GaN MQWs and therefore the optical properties of the InGaN/GaN MQWs change. The results shown here open up a possibility for the application of nitride semiconductors in magneto-optical and ME engineering. The novel phenomena discovered in this dissertation provides a more detailed understanding and potential applications of the composites consisting of semiconductor nanostructures, PCs, surface plasmons, and magnetic materials. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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