Two-Dimensional Transition Metal Dichalcogenides for Near Infrared Photodetection with an Eye toward Retinal Electrophysiology

Abstract

The successful isolation and characterization of graphene opened a new dimension for experimental materials research. And though graphene possesses an assortment of attractive mechanical, optical, and electrical properties the lack of a sizeable band gap has limited its use in several electronic and optoelectronic applications, such as in photodetectors. In the pursuit to overcome this obstacle a class of two-dimensional (2D) materials known as transition metal dichalcogenides (TMDCs) has garnered significant attention. This dissertation explores the underlying device physics and use of different 2D TMDCs for near infrared (NIR) photodetection with a consideration for a specific biological application. PdSe2 phototransistors are shown to have thickness dependent wavelength peaks in the near infrared region likely resulting from strong interlayer coupling due to its underlying puckered pentagonal structure. Gate-tunable photo response speed is demonstrated in vertical BP-MoS2 heterojunctions. And enhanced optoelectronic properties are exhibited in the charge density wave phase of TiSe2. These 2D TMDC NIR photodetectors all show significant improvements in their relative photodetection speeds and offer insight into future optoelectronic device engineering. Additionally, retinal electrophysiology is performed ex-vivo using perforated microelectrode arrays on mice retina to establish results and implications for future 2D material devices.