Mg-Doping-Concentration Dependence for Ni/p-GaN Schottky Contacts

Abstract

Mg-doping-concentration dependence in p-GaN Schottky contacts was characterized by current-voltage (I-V), photoresponse (PR), and photocapacitance (PHCAP) measurements. Mg-doped p-GaN films were grown on sapphire using metalorganic chemical vapor deposition. The Mg concentration was varied from 1.3 to 20×10¹⁸ cm^-3. After buffered hydrofluoric acid treatment, 100-nm-thick Ni films were deposited by electron-beam evaporation to form Schottky contacts. In the I-V characteristics, a memory effect was observed, and large Schottky-barrier-height (qϕ_B) (over 2 eV) was obtained for the samples with low-Mg-doping concentration. As the Mg doping concentration increased, the diodes became leaky, and the apparent qϕ_B decreased. For all the samples, large PR signals were detected, and qϕ_B values were determined to be as high as around 2.1-2.4 eV independently of the Mg doping level. We found that PR measurements have an advantage to characterize heavily-doped p-GaN contacts. In addition, because the threshold energy in the PHCAP results was consistent with the qϕ_B value, it can be considered that acceptor-type defects induced the Fermi level pinning.