Effects of the fluorine plasma treatment on the surface potential and Schottky barrier height of AlxGa1−xN/GaN heterostructures

摘要

The variations in surface potential and the Schottky barrier height u0002B in fluorine-plasma-treatednAlxGa1−xN/GaN heterostructures are systematically studied by x-ray photoelectron spectroscopy,nproviding insights to the mechanisms underlying the strong threshold voltage u0002Vthu0003 modulationnachieved by the F plasma treatment technology. It is found that a large amount of AlF3 appeared onnthe surface after the treatment, indicating a fluorinated surface. In addition, the surface potential ofnAl0.25Ga0.75N/GaN heterostructure was increased by u00040.38 eV during the first 60 s of the treatmentnand then rises slowly with additional treatment. Annealing at 400 °C in N2 ambient for 10 min doesnnot affect the surface potential, but results in quick reduction in AlF3, consistent with the relativenpoor thermal stability of AlF3 reported in literature. u0002B between Ni and F-plasma-treatednAl0.25Ga0.75N surface was extrapolated from the shift in Ga 2p3/2 core-level and exhibits a smallnincrease of 0.20 eV. The enhanced u0002B is much smaller than the positive shift in Vth observed fromnhigh electron mobility transistors fabricated with the same treatment conditions, suggesting that thenprimary factor responsible for the conversion from depletion-mode to enhancement-modenAlxGa1−xN/GaN by F plasma treatment is not the surface modifications but rather the negative fixedncharges carried by F ions in AlxGa1−xN/GaN heterostructures.