Sheremet V. Ohmic and barrier contacts based on titanium and zirconium borides to gallium nitride microwave diodes.

The thesis deals with investigation of processes occurring in multilayer ohmic and barrier contacts to n-GaN, with titanium and zirconium borides as diffusion barriers, subjected to active treatments. It is determined that the Ti-Al-TiBx-Au ohmic contacts and Ti(Zr)Bx-Au barrier contacts to n-GaN retain their structure and electrophysical properties up to the annealing temperatures of 900°C and to the dose of gama-irradiation up to 10^6 Gy. Structural-impurity ordering is observed at the interface between the contact metallization phases exposed to 60Со gama-irradiation (dose of 10^4 Gy). It manifests itself as decrease of contact resistivity and excess leakage currents for the ohmic and barrier contacts, respectively. Metallic conductivity through shunts is characteristic for the contact Au-TiBx-Al-Ti-n-GaN in the 270-380 K temperature range. Field emission becomes typical mechanism of current transport for contacts subjected to microwave treatment. It is shown that the tunnel mechanism of current transport through dislocation line is characteristic of the Au TiBx n-GaN barrier contact.