Colloidal Quantum Dot Absorption and Luminescence for Optoelectronics: From Machine Learning to Plasmonic-Enhanced Devices

Abstract

Colloidal quantum dots are nanometer-sized crystalline semiconductor nanoparticles. Owing to the quantum size effect, optoelectronic properties of colloidal quantum dots can be tuned, and thus optimized for a specific application. Due to the wet chemical synthesis through which these semiconductor nanoparticles are fabricated, they offer a cost-efficient way of integrating optically active semiconductors into existing state-of-the-art photonic and electrical circuitry. Ultimately, colloidal quantum dots are envisaged as an efficient and cheap replacement for current epitaxial technologies used in present optoelectronic devices. For optimal utilization of colloidal quantum dots in optoelectronic devices, there are two most important aspects to consider: understanding the material properties of colloidal quantum dots and optoelectronic design optimization given those material properties. This dissertation focuses on these two aspects. In the first part of this work, we focus on the understanding of optical properties of novel colloidal nanoparticles through efficient and machine-learning assisted data analysis. Optical properties of colloidal quantum dots are usually obtained through plethora of time-resolved spectroscopy techniques. One of the most prominent and standard spectroscopy techniques is time-resolved photoluminescence. In this work, a machine learning code to analyze time-resolved photoluminescence data without any a priori assumptions will be presented. As a validation step, we analyze computer-generated time-resolved photoluminescence datasets and show its benefits for analyzing the optical properties of colloidal quantum dots. In the second part of this dissertation, we utilize plasmonic metamaterials in order to enhance light absorption of colloidal quantum dot thin-film. By engineering metamaterials to minimize the reflection from our detectors, we demonstrate highly sensitive and tunable metasurface-enhanced photodetectors based on PbS colloidal quantum dots. In addition, a fabrication platform in which optimized photoconductors and photodiodes can be seamlessly fabricated together is presented. Fabricated devices feature responsivities of up to 8000 A/W with low noise equivalent powers in the order of 10s of pW/√Hz. Finally, we demonstrate Schottky barrier photodiodes with responsivities of ~5 mA/W that offer fast responses with 13/23 μs rise/fall times. The fabrication platform for metasurface enhanced photodetectors is versatile in that its resonant wavelength can be easily tuned by using different nanocrystals and rescaling the metasurface features. In addition, low voltages used in operation of metasurface photoconductors make them compatible with CMOS read-out circuitry.