Study of the flat band voltage shift of metal/insulator/n-GaN capacitors by annealing

The flat-band voltage (V-FB) of metal/insulator (SiN or SiO2)/n-GaN capacitors has been investigated focusing on the effect of postdeposition annealing (PDA). We have found that V-FB shifts toward the negative-bias direction with increasing annealing temperature. The estimated activation energies of a trap related to the shift in V-FB are approximately 160 meV for SiN and 130 meV for SiO2. The difference between these energies is small. The dependence of V-FB on SiN thickness indicates that fixed charges causing the shift in V-FB exists at the SiN/GaN interface. This implies that the reactions at both the SiN/GaN and SiO2/GaN interfaces are promoted by the same mechanism. We propose an interface dipole model to explain the shift in V-FB. During the deposition of the insulator, each dipole is in a random direction, because the process reaction is carried out at room temperature. It is considered that PDA might cause the randomly oriented dipoles to face in the same direction, resulting in the total moment of the dipoles becoming larger than that before, annealing. We also performed Kelvin force microscopy (KFM) measurement to observe the charged state of SiN directly. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim