Reduced surface leakage current and trapping effects in AlGaN/GaN high electron mobility transistors on silicon with SiN/Al2O3 passivation

The surface leakage currents and the surface trapping effects of the AlGaN/GaN high electron mobility transistors (HEMTs) on silicon with different passivation schemes, namely, a 120 nm plasma enhanced chemical vapor deposited SiN, a 10 nm atomic layer deposited (ALD) Al2O3 and a bilayer of SiN/Al2O3 (120/10 nm) have been investigated. After SiN passivation, the surface leakage current of the GaN HEMT was found to increase by about six orders; while it only increased by three orders after the insertion of Al2O3 between SiN and AlGaN/GaN. The surface conduction mechanism is believed to be the two-dimensional variable range hopping for all the samples. The leakage current in the etched GaN buffer layer with SiN/Al2O3 bilayer passivation was also much smaller than that with only SiN passivation. The pulse measurement shows that the bilayer of SiN/Al2O3 passivation scheme can effectively reduce the surface states and suppress the trapping effects.