Quantum dot integrated silicon photonic devices for optical sensor applications

Abstract

Optical sensors have been ubiquitous in laboratories for several decades for applications including healthcare diagnostics, personalized radiation safety badges, and space radiation dosimeters. However, there remains a need to develop and broaden the availability of highly sensitive sensors for healthcare diagnostics that are low-cost and usable by untrained personnel, and to improve the energy resolution and data acquisition time of low-cost optical radiation dosimeters. This work aims to utilize advances in silicon photonics to develop optical sensors with improved performance metrics of sensitivity, cost, and ease of use. These optical sensors combine two different classes of materials – porous 3D scaffolds of silicon and colloidal quantum dot (QD) light emitters – for their inherently advantageous materials and optical properties. Through careful optimization of the porous sensing platform for size selective, QD-labeled, target analyte capture, we demonstrate a dual-mode optical sensing scheme based on thin-film interferometry that exploits a porous silicon-QD nanocomposite material to provide highly sensitive and accurate bio-detection capabilities. The net changes in effective refractive index of the porous silicon sensor provide quantitative information on the captured target biomolecule while target-specific QD photoluminescence spectra provide a secondary means of target identification that can facilitate multi-analyte detection. The design of porous silicon annular Bragg resonators integrated with QD light emitters for the highly sensitive and label-free detection of small molecules is also presented. Porous silicon-QD films are also characterized for their ability to respond to high energy radiation. The degree of QD photodarkening under highly ionizing sources of radiation, including X-rays and gamma-rays, can be directly related to the total exposure dose. The interactions of high energy photon states with QDs result in loss of surface ligands that introduce several mid-gap defect states and long lived carrier trap sites. By exposing the QDs within the porous silicon films to a ligand containing re-passivation solution, nearly complete reversibility of radiation-induced photodarkening can be achieved. This work demonstrates the exciting possibilities of engineering large area, flexible, low-cost, QD-based optical dosimeters that can provide a simple, color-coded read-out that corresponds to the total exposure dose.