Ion implanted ohmic contacts to AlGaN/GaN structures

Implantation of silicon ions was used for the ohmic contact resistance improvement in AlGaN/GaN and GaN epitaxial layers on sapphire. 28 Si+ ions with a dose 2 x 1015 cm2 and energy 80 keV were selectively implanted using a photoresist mask. Implanted samples were RTP annealed in temperatures up to 1250 grad C in nitrogen ambient using unprotected surface method and proximity geometry method with a dummy GaN/sapphire wafer as the cover. Post-annealed sample surface was studied by SEM, AFM and EDS methods. High density of 1 μm size defects on unprotected surface samples was observed. The proximity method resulted in good surface quality without defects. Ohmic contact Ti/Al/Ni/Au multilayer was electron beam evaporated and RTP annealed at 850 grad C. The ohmic contacts fabricated in the Si implanted regions revealed the specific contact resistance of 1.5 x 10-5 Ω cm2, in comparison to 8 x 10-5 cm2 that means fivefold improvement of the ohmic contact resistance was obtained due to ion implantation processing. (authors)