Fluorine-based plasma treatment for hetero-epitaxial β-Ga2O3 MOSFETs

In this work, we demonstrate the lateral metal-oxidesemiconductor field-effect transistors (MOSFETs) with beta-Ga2O3 film (thickness = 150 nm) grown on a c-plane sapphire substrate by a hydride vapor phase epitaxy (HVPE) method using a CF4-based plasma treatment. By incorporating fluorine (F) the electrical characteristics of the surface and bulk regions of the resistive beta-Ga2O3 film could be significantly improved. The analyses by secondary ion mass spectrometry and x-ray photoemission spectroscopy confirmed the formation of the substitutional fluorine, F-O, with its peak concentration of 2.3 x 10(18) cm(-3) at 5 similar to 10 nm deep from the surface and about 10(15) similar to 10(16) cm(-3) in the bulk region. While the argon-plasma treatment was insufficient for making a Ti/Au/Ti metal contact ohmic, the same contact formed on the CF4-treated surface showed an ohmic behavior with specific resistivity of 2.0 x 10(-3) Omega.cm(2) and contact resistance of 0.8 Omega.m without any post thermal annealing. With the improvement of the electrical properties in both the surface and bulk regions, the HVEP-grown heteroepitaxial beta-Ga2O3 MOSFET exhibited the field-effect mobility of up to 5.3 cm(2)/V.s and on/off ratio of 10(6).

Automated summary

The electrical characteristics of beta-Ga2O3 film were significantly improved using CF4 plasma treatment, allowing the MOSFET to exhibit improved field-effect mobility and on/off ratio. The incorporation of fluorine enhanced both surface and bulk properties of the material, leading to successful ohmic contact formation without post-thermal annealing.