Dr. Chanyoung Yim: Investigation of Vertically Stacked Hybrid Devices
Conductive carbon thin films are known to be promising candidates for future electrode materials for micro/nano-electronic device applications due to their favourable electrical properties and diversity of formation. In particular, recent enormous interest in graphene, a two-dimensional carbon material, has triggered many broad and comprehensive studies not only on graphene itself, but also on other two-dimensional layered materials such as transition metal dichalcogenides. The introduction of such materials to real electronic device applications can be effectively achieved by making hybrid devices where these materials are combined with conventional semiconductors in device fabrication. Therefore, it is very important to understand and define the electrical characteristics of such hybrid devices thoroughly in the initial stages of research. In this study, two types of hybrid electronic devices such as Schottky barrier diodes and photodiodes have been realised using conductive carbon materials and a semiconducting transition metal dichalcogenide thin film. Material properties have been characterised by a number of techniques and integrated with standard silicon technology. The electrical characteristics of the resulting devices have been investigated using several experimental techniques.
First, Schottky barrier diodes have been fabricated on silicon substrates using three different conductive carbon thin films namely pyrolytic carbon, glassy carbon from pyrolysed photoresist and graphene. Important electrical parameters of the Schottky diodes including the Schottky barrier height, the ideality factor, and series resistance are extracted by analysing the dc current-voltage measurement data. Furthermore, ac impedance spectra of the Schottky diodes are measured. The impedance data of the devices can be interpreted by simulating the experimental data using a developed equivalent circuit model.
Next, vertically stacked p-n heterojunction diodes consisting of a thin n-type molybdenum disulfide film and p-type silicon have been investigated. A vapour phase sulfurisation process is used to grow continuous large-scale molybdenum disulfide thin films from pre-deposited molybdenum metal layers on insulators. The n-type molybdenum disulfide thin films are transferred onto the pre-patterned p-type silicon substrates, forming p-n heterojunction diodes. The fabricated large-scale p-n heterojunction diodes show notable photoconductivity which can be tuned by modifying the thickness of the molybdenum disulfide layers. Moreover, spectral response measurements reveal that the p-n heterojunction diodes have a broad spectral response resulting from direct and indirect band transitions of the nanoscale molybdenum disulfide thin films.
Room: H-E 308