Sen Huang1, Hongwei Chen1, Kevin J. Chen2
1Department of Electronic and Computer Engineering; Hong Kong University of Science and Technology; Clear Water Bay Kowloon,Hong-Kong
2Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
Tóm tắt
AbstractThe variations in surface potential and the Schottky barrier height ΦB in fluorine‐plasma‐treated AlxGa1‐xN/GaN heterotructures are systematically studied by x‐ray photoelectron spectroscopy (XPS), giving insights into the mechanisms underlying the strong threshold voltage shift in AlxGa1‐xN/GaN HEMTs by the F plasma treatment technology. It is found that the treatment resulted in a fluorinated surface containing masses of AlF3, with the surface potential of Al0.25Ga0.75N/GaN heterostructure increased by ∼0.38 eV during the first 60 seconds of the treatment. Annealing at 400 °C in N2 ambient for 10 minutes does not affect the surface potential, but results in quick reduction of AlF3, consistent with the relative poor thermal stability of AlF3 reported in literature. ΦB between Ni and F‐plasma‐treated Al0.25Ga0.75N surface was extrapolated from the shift in Ga 2p3/2 core‐level and exhibits a small increase of 0.20 eV. The enhanced ΦB is much smaller than the positive shift in Vth observed from HEMTs fabricated with the same treatment conditions, suggesting that the primary factor responsible for the conversion from depletion‐mode to enhancement‐mode AlxGa1‐xN/GaN by F plasma treatment is not the surface modifications, but rather the negative fixed charges carried by F ions in AlxGa1‐xN/GaN heterostructures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
