Ohmic and Schottky contacts to gallium nitride: The influence of processing on properties

Electrodeposited Pt and sputtered Ni/Pt contacts to p-GaN (p = 4.6 x 1017 cm-3) are reported and compared to sputtered Ni, Pt, and Ni/Au contacts and electron beam and thermally evaporated Ni contacts. Sequential rapid thermal annealing was employed with samples receiving an initial five minute heat treatment of 400°C followed by one minute anneals at 500, 600, and 700°C, all under flowing N2. Plots of current versus voltage for all contacts showed nonlinearity through the origin as deposited and for all annealing conditions. Electrodeposited, DC magnetron sputtered, and electron beam evaporated Pt contacts to n-GaN (n = 1.5 x 10 17 cm-3) are also reported. All contacts were rectifying in the as-deposited condition and values of the barrier height were determined by current-voltage and capacitance-voltage measurements. The influence of deposition conditions on the electrical characteristics of the sputtered and electrodeposited Pt contacts was further studied, and strong dependencies of the barrier height were observed. Additionally, a dependence of the barrier height with time following deposition is shown. Taking into consideration all parameters of this study, the barrier height could be made to differ by as much as 0.65 eV by I-V measurements and 0.64 eV by C-V measurements with I-V and C-V barriers as high as 1.43 and 1.57 eV, respectively. Reverse current densities are reported for a -5 V bias and usually showed trends in accordance with the reported barrier heights with a difference between the highest and lowest mean and median values of a factor of 103 and 104, respectively. The electrical properties are believed to be strongly influenced by the presence of electrically active defects introduced during metal deposition. Deep level transient spectroscopy data support this hypothesis.