Zn acceptor position in GaN:Zn probed by contactless electroreflectance spectroscopy

Abstract

The Zn acceptor level position in GaN:Zn was studied on specially designed GaN(undoped)/GaN:Zn([Zn] = 5 × 1016 cm−3) structures by contactless electroreflectance. A well-defined Franz-Keldysh oscillation is present in optical spectra which results from the built-in electric field present in the near-surface layer. The obtained results show that a significant band bending in the GaN:Zn layer occurs lowering the field in the top layer that is in line with predictions for a semiconductor doped with a high ionization energy acceptor. The acceptor level responsible for the Fermi level position in GaN:Zn is found to be at ∼2.3 eV below the conduction band minimum which coincides with levels introduced by Zn atoms substituting nitrogen in the lattice. At the same time, the surface Fermi level of structures is located in the middle of the bandgap, which is in the lower maximum of (0001) GaN surface density of states.