Mg-doping-concentration dependence for Ni/p-GaN schottky contacts

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 (qφB) (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 qφB decreased. For all the samples, large PR signals were detected, and qφB 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 qφB value, it can be considered that acceptor-type defects induced the Fermi level pinning. © 2020 The Society of Materials Science, Japan.