ION IMPLANTED OHMIC CONTACTS TO AlGaN/GaN STRUCTURES
Bogusław Boratyński – Wojciech Macherzyński – Andrzej Droździel – Krzysztof Pyszniak
Implantation of silicon ions was used for the ohmic contact resistance improvement in AlGaN/GaN and GaN epitaxial layers on sapphire. 28OSi+ ions with a dose 2×1015 cm and energy 80 keV were selectively implanted using a photoresist mask. Implanted samples were RTP annealed in temperatures up to 1250°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 1μm 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°C. The ohmic contacts fabricated in the Si implanted regions revealed the specific contact resistance of 1.5×10-5 Ωcm2, in comparison to 8×10-5 Ωcm2 that means fivefold improvement of the ohmic contact resistance was obtained due to ion implantation processing.
Keywords: ion implantation, heterostructure, AlGaN/GaN, ohmic contacts