In situ Mg surface treatment of p-type GaN grown by ammonia-molecular-beam epitaxy for efficient Ohmic contact formation

Tang, H.; Bardwell, J. A.; Webb, J. B.; Rolfe, S.; Liu, Y.; Moisa, S.; Sproule, I.
February 2003
Applied Physics Letters;2/3/2003, Vol. 82 Issue 5, p736
Academic Journal
The pronounced effect of in situ Mg surface treatment of p-type GaN grown by ammonia-molecular-beam epitaxy on Ohmic contact formation is reported. The surface of the Mg-doped p-type GaN layer was held at the growth temperature following the growth, and exposed to a Mg beam under a NH[sub 3] flow for 15 min. With such a treatment, a specific contact resistance in the low 10[sup -4] Ω cm² was obtained with as-deposited Ni/Au contacts and without any ex situ treatment. In contrast, contacts on similar p-type layers without such an in situ treatment were highly rectifying even after annealing. A surface Fermi level shift as a result of the in situ treatment was observed by x-ray photoemission studies, and is ascribed, together with the high surface doping concentration, to be the mechanisms behind the effective Ohmic contact formation.


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