|M.Sc Student||Katz Matias|
|Subject||III-Nitrides Intersubband Based Quantum Cascade Detectors|
with Enhanced Performance by Optical Nano-Structur
|Department||Department of Electrical Engineering||Supervisors||Professor Meir Orenstein|
|Professor Emeritus Gad Bahir|
|Full Thesis text|
The quantum cascade detector (QCD) has emerged in recent years as an alternative for quantum well infrared photodetector. Wide-gap III-nitride semiconductors have emerged as excellent candidates for near-infrared QCD, thanks to the large conduction band offset provided by their heterostructures, the wavelength tenability and high-speed operation. The fundamental building-block of a QCD consists of an active quantum well (QW) where electron excitation occurs upon photon intersubband (ISB) absorption, and multi-quantum well extractor that transfers the excited electron to the ground level of the following active QW. Major drawback of the QCD in applications based on normal light incidence is related to the polarization selection rule of QW ISB transitions, allowing absorption only for an electric field polarized perpendicular to the QW layers. Another deficiency is the relatively small absorption cross section of each QWs.
Using plasmonic nanostructures embedded in GaN-based QCD detectors, could be of tremendous importance for application perspectives. In this work we propose two new different normal incident light coupling antennas solutions for the previously introduced drawbacks. First, the use of a two-dimensional metallic hole array (MHA) allows the coupling of surface plasmons (SP) waves to the absorption region of the QCD. The generated SP mode exhibits a dominant electric field component normal to the surface that is the proper polarization for exciting the ISB resonance. The second light coupling scheme involves planar "H" nanoantenna arrays. Incoming normal incidence light is transferred into the z component of the electric field and is strongly localized underneath the antenna. Consequently, the Ez field can strongly interact with the ISBT of the detector. We present the design, realization and full characterization of nanoantennas-integrated normal incidence infrared QCD. Specifically, we demonstrate the detection for a signal enhancement of up to a factor of 12 compared to the standard wedge illumination characterization. In addition, using the ISBT QCD as an electronic two-level system and "H" nanoantenna with deep-subwavelength mode-volumes, we demonstrate normal incidence room temperature strong-coupling, with Rabi splitting on the order of 6% of the fundamental bare cavity frequency at short wave infrared spectral region.