Formation of low-resistance Ohmic contacts to N-face n-GaN for high-power GaN-based vertical light-emitting diodes

We report on the formation of low-resistance Ohmic contacts to N-face n-GaN for high-power vertical light-emitting diodes using an Al-Ga solid solution (50 nm)/Ti(30 nm)/Al(200 nm) scheme and compare them with Ti(30 nm)/Al(200 nm) contacts. The Al-Ga solid solution layer is introduced to minimize the formation of Ga vacancies near the N-face n-GaN surface. It is shown that, unlike the Ti/Al contacts, the Al-Ga solid solution/Ti/Al contacts exhibit Ohmic behavior with a resistivity of 4.1 X 10(-4) Omega cm(2), even after annealing at 250 degrees C. X-ray photoemission spectroscopy and secondary ion mass spectrometry examinations are performed to understand the temperature dependence of the electrical properties. (C) 2010 American Institute of Physics. [doi:10.1063/1.3484152]