Ohmic contacts on (111)-oriented phosphorus-doped diamond fabricated by FIB transformation and surface Ga+ implantation

Among the ultra-wide bandgap (UWBG) materials, diamond has unique properties for high power device applications and can deliver p-type and n-type doping. However, the achievement of low resistive ohmic contacts on n-type diamond limits the fabrication of bipolar devices. This study investigates the use of focused Ga + ion beam (FIB) to fabricate metal-free ohmic contacts on phosphorus-doped diamond, with a doping concentration of ~5 × 10 18 cm −3 estimated by cathodoluminescence. FIB irradiation was used to locally modify the diamond surface, resulting in a conductive channel with ohmic, albeit highly resistive, behaviour. Using the circular Transfer Length Method (cTLM), a specific contact resistance of 4.3·10 4 Ω·cm 2 was obtained. This value is consistent with state-of-the-art results at similar doping levels, demonstrating that FIB is a viable and efficient technique for contact formation in diamond-based electronic devices. • Fabrication of ohmic contacts on (111) P-doped diamond via FIB. • Single-step process without metal deposition, under 2 min per contact. • Conductive layer formed via Ga + implantation and sp 2 carbon amorphization. • cTLM shows low specific contact resistance: ρc ≈ 4.3 × 10 4 Ω·cm 2 . • Efficient, cost-effective alternative to conventional multi-step metallization.