Thermalization and exciton localization in 2D semiconductors

Abstract

2D semiconductors are a promising class of materials to investigate for applications in the next generation of photonic devices. They can be used to generate quantum light and also exhibit correlated many-body phenomena. Many of the novel optoelectronic properties of 2D semiconductors are associated with strongly-bound hydrogen-like states known as excitons. Excitons in 2D semiconductors have binding energies on the order of 100s of meV and are stable at room temperature. At low temperatures, higher-order excitonic states such as charged excitons and biexcitons--multiple-bound excitons that are like hydrogen molecules-- and localized excitons that emit quantum light are also observed. Whether excited optically or electronically, a diversity of high-energy excitons and free carriers are produced directly after excitation. The relaxation and thermalization of these initial states influence the formation of excitons, biexcitons, and localized excitons. Here, I present work that (i) investigates the thermalization of excited states in a prototypical 2D semiconductor, monolayer (1L-) WSe2, and reports the discovery that the generation of charged biexcitons is enhanced with increasing photoexcitation energy, (ii) shows the emergence of quantum emitters (QEs) in a new 2D QE platform: 1L-WSe2 nanowrinkle arrays induced by Au nano stressors, and (iii) uses a novel method to classify the excited-state dynamics of 2D QEs and differentiate emitter populations. A suite of low-temperature energy- and time- resolved optical spectroscopies are used to conduct this work. This work shows how excited state thermalization affects the formation of exciton and biexcitons and investigates the optical properties of an emergent class of 2D quantum light emitters.