The growth and development of semiconductor hyperbolic metamaterials for the infrared
Date
2021
Authors
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Publisher
University of Delaware
Abstract
Layered hyperbolic metamaterials (HMMs) are highly anisotropic, composite materials composed of subwavelength metal and dielectric layers. The subwavelength structure of HMMs allow engineers to design materials with novel, macroscopic optical properties, such as a hyperbolic isofrequency surface and the ability to support large wavevector modes. HMMs have been studied for years in the visible wavelength regime; however, the subwavelength metal and dielectric materials used in the visible range are incompatible with other wavelength regimes. With the discovery that doped III-V semiconductors can be used as optical metals in the infrared, HMMs have begun to be investigated as a potential pathway to improve the performance of infrared optoelectronic devices. ☐ This dissertation begins by analyzing multiple HMMs composed of different semiconductors to determine which combination of semiconductors results in the highest quality HMM. The metric used to determine the best HMM was the quality factor of the bulk large wavevector modes in the HMMs—called volume plasmon polaritons (VPPs). VPPs arise from the coupling of surface plasmon polaritons that are present at each metal and dielectric interface and are responsible for supporting the large wavevector light within the HMM. The study determined that Si:InAs/AlSb resulted in the highest quality HMM due to the large conduction band offset between the two materials. This conduction band offset led to more confined surface plasmon polaritons which in turn gave rise to higher quality VPPs. ☐ The next section investigated how the subwavelength structure of an HMM impacts the resonant position of the VPP modes. We also set out to determine if the effective medium analysis (EMA)—a common approximation used for HMMs—can accurately predict the resonant position of the VPP modes. Using the finite element method (FEM) to model HMMs with different number of periods and different period thicknesses, we determined that so long as the period thicknesses are sufficiently subwavelength, that the subwavelength structure has minimal impact on the resonant position of the VPP modes. However, the overall thickness of the HMM has a significant impact on the VPP mode resonant position. Then, by comparing the results from FEM with predictions from EMA, we determined that EMA does not accurately predict the resonant positions of the VPP modes due to an inability to account for boundary conditions at the bottom interface of the HMM. ☐ After understanding how to design a high-quality HMM for the infrared, we moved on to investigating potential applications for HMMs in the infrared. First, we examined the thermal emission spectra from a Si:InAs/AlSb HMM. We were able to show that it is possible to outcouple the VPP modes into the far field with the use of a grating coupler. Next, we investigated the possibility of strong coupling the VPP modes in an HMM to the intersubband transition in an InAs/AlSb quantum well embedded in the dielectric layers. We were able to show anti-crossing in the reflection spectra, which is indicative of strong coupling. ☐ This dissertation demonstrates knowledge of how to grow and design high quality, layered, semiconductor HMMs for the infrared. It also explores potential applications for HMMs and lays the groundwork for the incorporation of HMMs into semiconductor optoelectronic devices for the infrared.
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Keywords
Infrared, Metamaterial, Semiconductor, Strong coupling