Large-Area Nanometer-thin β-Ga_2O_3 Films Synthesized via Oxide Printing of Liquid Metal Gallium

摘要

Exfoliated gallium oxide (Ga_2O_3) has been reported as an ultrathin channel material in field-effect transistors. Unlike in 2D materials with van der Waals forces between stacked layers, weak bonding in β-Ga_2O_3 along the (100) direction enables mechanical exfoliation. The thickness of these exfoliated films has been limited to tens to hundreds of nanometers. Here we summarize our latest work, which followed the process developed by Carey et al, enabling us to attain ～2 nm thick Ga_2O_3 films over a large surface area (> 1 mm~2). The films are characterized using optical microscopy, AFM, XPS, Raman spectroscopy, photoluminescence (PL), and TEM. Optical microscope images showed color changes to the film upon annealing. AFM revealed the film thickness to be as thin as 2 nm over areas » 1 mm~2. XPS and Raman spectra revealed characteristic signatures of P-phase Ga_2O_3. Characteristic PL of Ga_2O_3 was seen in all samples with overall intensity of luminescence increasing after annealing, attributed to increased crystallinity and grain size. Changes in PL after annealing are associated with an increase in oxygen interstitials and a decrease in oxygen vacancies. Lastly, TEM analysis revealed the film as p-phase Ga_2O_3 polycrystalline. Overall, our results demonstrate that annealing of thin films obtained from oxide printing of liquid metal Ga is a non-expensive and straightforward process that can lead to P-Ga_2O_3 films that are nanometer-thin over wafer-scale areas.