Material properties and device applications of ferroelectric In2Se3 and high-mobility InSe
Open Access
- Author:
- Rodriguez, Justin
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 14, 2021
- Committee Members:
- Chaoxing Liu, Major Field Member
Tom Jackson, Outside Unit & Field Member
Zhiqiang Mao, Major Field Member
Ying Liu, Chair & Dissertation Advisor
Nitin Samarth, Program Head/Chair - Keywords:
- InSe
In2Se3
ferroelectricity
2D materials - Abstract:
- Modern microelectronics seeks to miniaturize transistors and follows Moore’s Law, seeking faster logic, lower power usage, and denser storage. Progress in this direction can no longer rely on traditional techniques and materials, as fundamental limits to materials become more significant as devices shrink. In this dissertation I present work I carried out in collaboration with other researchers, which includes crystal characterization and transport measurements on two layered indium-selenium compounds featuring van der Waals interlayer coupling, γ-InSe and α-In2Se3, that may provide new avenues to advance microelectronics. I first review back ground information on semiconductors, field effect transistors, ferroelectricity, and layered transition metal chalcogenides. I summarize experimental methods including device preparation and measurements. I then present our work on α-In2Se3 ferroelectric-field effect transistors (FeSmFET). The devices are prepared from mechanically exfoliated ultrathin crystals, using α-In2Se3 for the channel layer. Contact to the crystal was done using a novel photolithography process and metal evaporation. In traditional ferroelectric field effect transistors the semiconducting channel is controlled using a ferroelectric-dielectric, this is reversed in a FeSmFET where the channel is a ferroelectric semiconductor. I present results of our transport measurements on the FeSmFET devices, evidence for polarization-controlled behavior and evidence for an electric-field-induced metallic state in thin crystals of α-In2Se3. Magneto electrical transport measurements revealed the effect of weak localization and high carrier densities in the metallic state. I also present our work on molecular beam epitaxy (MBE) grown films of γ-InSe on GaAs. Raman spectroscopy, X-ray diffraction, and transmission electron microscopy were used to characterize these films. Hall bar devices were then fabricated using photolithography and plasma etching. These films were found to be extremely resistive, with the temperature dependent resistivity measurable only above room temperature, showing insulating behavior. Through Hall effect measurements, these films of γ-InSe were found to show high mobility, typically reported in (encapsulated) exfoliated and a few thin film devices, though the films were found to not be electrically isolated from the underlying substrate. The transmission electron microscopy showed the presence of many stacking faults within the growth which may account for the high resistivity in the film and limit the mobility. Work on α-In2Se3 and γ-InSe presented in this dissertation shows the great potential of these two layered TMCs as electronic materials. Potentially providing an avenue to study ferroelectric dipoles in a metallic state and examine the interaction of polarization and conduction electrons. Our work also illustrates the potential application of molecular beam epitaxy grown InSe microelectronics.