First demonstration of hetero-epitaxial ε-Ga2O3 MOSFETs by MOCVD and a F-plasma surface doping

This letter reports on the demonstration of ε-phase gallium oxide (ε-Ga2O3) based metal-oxidesemiconductor field effect transistors (MOSFETs) for the first time. Phase-pure ε-Ga2O3 film was hetero-epitaxially grown on a sapphire substrate by metal organic chemical vapor deposition (MOCVD) using a two-step growth method. The high crystalline quality of the epilayer was confirmed with the X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) investigations. Through a proper surface cleaning and CF4-plasma treatment process, fluorine (F) atoms were incorporated and acted as donors in the ε-Ga2O3 film, by which the sheet resistance (Rsh) of the epilayer was decreased by 105. Based on this F-plasma doped ε-Ga2O3 film, MOSFETs with a maximum output current density exceeding 3 mA/mm were successfully demonstrated. The doping profile extracted from the capacitance-voltage (C-V) measurement showed a significant carrier accumulation near the ε-Ga2O3 film surface with a peak concentration of 5 × 1017 cm−3 and an integrated carrier density of ∼6.4 × 1011 cm−2. The peak electron effective mobility (μeff) within the MOSFET channel was extracted to be as high as 19 cm2/Vs, indicating a great potential of ε-Ga2O3 based electronics for future high-speed and high-power applications.