Ohmic Contact to p-Type GaN Enabled by Post-Growth Diffusion of Magnesium

We demonstrated the formation of excellent Ohmic contact to ${p}$ -type GaN (including the plasma etching-damaged ${p}$ -type GaN which otherwise exhibited undetectable current within ±5 V) by the post-growth diffusion of magnesium. The specific contact resistivity on the order of $10^{-{4}}\,\,\Omega $ .cm ² (extracted at V = 0 V) was achieved on the plasma-damaged ${p}$ -GaN with linear current-voltage characteristics by the transfer length method (TLM) measurement. The improvement in current by a factor of over 10 ⁹ was also obtained on the plasma-damaged p-n junction diode after the same Mg-treatment. These experimental results indicate a great potential of post-growth diffusion of Mg to overcome the bottleneck of forming a good Ohmic contact to ${p}$ -GaN.