• ab-initio
• ald
• anderson
• beta
• cleanroom
• crystal
• density
• dft
• doped
• espresso
• fet
• film
• films
• functional
• Ga2O3
• gallium
• hall
• hln
• kaust
• laser
• localization
• magnetotransport
• mit
• Mott
• mott
• oxide
• phase
• pld
• ppms
• qe
• quantum
• silicon
• theory
• thin
• tio
• transistor
• transition
• uwbg
• vrh
• wl
• β
• β-Ga2O3

Gallium oxide (Ga2O3) is an emerging ultra-wide bandgap semiconductor and belongs to transparent conducting oxide materials. During the last years, it has attracted a growing interest due to its bandgap of 4.8 eV, its high thermal stability, its high breakdown electric field, and the reduced cost respect with to its competitors. It has been mainly studied for its properties and applications at high operating temperatures. Only a few of researches deal with the low-temperature characteristics of Ga2O3, which exhibits unconventional behaviors for its class of materials. This thesis explores the quantum properties at low temperatures of silicon doped β-Ga2O3 single crystal thin films grown using pulsed laser deposition (PLD). The investigation is conducted using magnetotransport measurements within a physical property measurement system (PPMS). To carry out these measurements, various Hall bars were created using advanced cleanroom techniques, such as UV photolithography, reactive plasma etching, reactive metal sputtering, metal evaporation, and atomic layer deposition (ALD).
Measurements were performed on the Hall bars to determine both the Hall resistance and the longitudinal resistance. These measurements were conducted over a temperature range of 2K to 300K, with and without the application of a perpendicular magnetic field spanning from -9T to 9T. Transport measurements showed consistent carrier concentration across the temperature range examined, with resistivity demonstrating variable range hopping (VRH) conduction at low temperatures, which is associated with the temperature-dependent localization length. Additionally, the longitudinal resistance displayed a significant reliance on the magnetic field, particularly at lower temperatures, revealing weak localization (WL) effects. To gain deeper understanding of these occurrences, the magnetic field dependence of VRH conduction was investigated, uncovering the capability to adjust localization, resulting in a transition from WL to strong localization (SL).
In order to augment our comprehension of the measured behavior and to supplement experimental inquiries, we conducted density functional theory (DFT) simulations. Our investigation delved into the examination of the Fermi level under different doping levels and the changes in the density of states. We observed the presence of a silicon-based impurity band situated just below the conduction band, providing an explanation for the observed VRH mechanism. The findings of this thesis present intriguing prospects for exploring fundamental physics in Ga2O3 and the advancement of a new generation of devices that leverage controllable localization, similar to Mott transistors.