Positron annihilation study of Pd contacts on impurity-doped GaN

Pd contacts on both n-type and p-type GaN were studied using positron annih ilation spectroscopy, and the results were used to interpret the role of Ga vacancies on the band bending below the contacts. The concentration of Ga vacancy in Si-doped GaN was higher than that in the Mg-doped one. In Si-dop ed GaN, implanted positrons were annihilated at the nearer surface region a nd the interface of Pd/n-type GaN was detected by positrons clearly shifted toward the surface of Pd. This suggests that Ga vacancies could act as an interface state, pinning the Fermi level at the interface of Pd with GaN, l eading to the production of a negative electric field below the interface. (C) 2001 American Institute of Physics.