Design and Realization of Nano-scale Semiconductor Lasers
| Autor: | Chou, Bo-Tsun, 周柏存 |
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| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 Quest of searching for small coherent light sources has never been stopped for these micro-to-nano scale light sources are not only practically essential for small footprint, low power consumption, high density, optical integrated circuit and parallel signal processing applications but also provide insightful way to investigate the interaction between light and matter. Several designs have been developed to scale down the optical cavity volume to contain only few photons modes, such as photonic crystal defect type lasers, microdisk lasers, and nanowire lasers. These lasers, however, require the cavity size in the order of few (/n)3 to sustain a proper mode profile with a reasonable cavity Q value. Recently, optical cavities surrounded with metal claddings have been developed to reduce the cavity volume because the optical field penetrating into the metal claddings decay so rapidly that the optical mode can be further shrunk at the cost of a lower cavity Q value because of the strong absorption of metal. However, metal can provide a method of drastically diminishing the cavity mode beyond the diffraction limit by forming the surface plasmon at the interface of metal and dielectric layers. The ultra-small electromagnetic field distribution of the surface plasmon mode can substantially facilitate the interaction between light and matter by enhancing the Purcell factor. Successful demonstration of a plasmon nanolaser typically relies on its enhanced Purcell factor, which is inversely proportional to the mode volume. In addition, the slower propagating speed of plasmons can raise the Purcell factor by increasing opportunities for interaction between the gain medium and surface plasmons. Slow group velocity can be achieved at the band edge provided by the distributed feedback mechanism in the two dimensional periodic structure. However, the distributed feedback mechanism requires a relatively large area, which violates the small dimension requirement of nanolasers. The refractive index of silver (Ag) has a high variation at the ultraviolet (UV) wavelength range because of the interband absorption. This index variation can directly influence the dispersion of the surface plasmon to achieve a large group index, resulting in a small mode volume and large Purcell factor. To demonstrate this effect, we used the zinc oxide (ZnO) nanowire as the gain medium to match the UV wavelength range. We adjust the dielectric spacer thickness to tune the surface plasmon dispersion curve so that the lasing wavelength can be located at a large dispersion region, thereby achieving a low group velocity, which is of 1/80 of the speed of light. Beside, we also presented a high-performance Al-based plasmonic nanolaser in the ultraviolet regime. The interfacial roughness and, in particular, metal film quality play a key role in the ZnO nanolasers. By using molecular beam epitaxy to grow a high-quality single-crystalline Al film, followed by ultra-smooth Al2O3 layer prepared by atomic layer deposition and ZnO nanowire placement, we have realized an ultraviolet plasmonic nanolaser with a very low threshold pumping energy density (0.28mJ/cm2) and a high characteristic temperature (178K). |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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