This paper concentrates on the impact of SiN passivation layer deposited by plasma-enhanced chemical vapor deposition(PECVD)on the Schottky characteristics in GaN high electron mobility transistors(HEMTs).Three types of SiN layers with different deposition conditions were deposited on GaN HEMTs.Atomic force microscope(AFM),capacitance-voltage(C-V),and Fourier transform infrared(FTIR)measurement were used to analyze the surface morphology,the electrical characterization,and the chemical bonding of SiN thin films,respectively.The better surface morphology was achieved from the device with lower gate leakage current.The fixed positive charge Qf was extracted from C-V curves of Al/SiN/Si structures and quite different density of trap states(in the order of magnitude of 1011-1012 cm-2)was observed.It was found that the least trap states were in accordance with the lowest gate leakage current.Furthermore,the chemical bonds and the％H in Si-H and N-H were figured from FTIR measurement,demonstrating an increase in the density of Qf with the increasing％H in N-H.It reveals that the effect of SiN passivation can be improved in GaN-based HEMTs by modulating％H in Si-H and N-H,thus achieving a better Schottky characteristics.