Impact of Si⁺ implantation on reduction of contact resistance in Ti/Al contact to GaN

Abstract

For the Ti/Al contact to n‐type GaN, the impact of Si+ implantation on the reduction of contact resistance is investigated. The undoped GaN, grown on the sapphire substrate, is implanted by Si ions with the energy of 150 keV at the dose ranging from 5 x 1013 to 5 x 1014/cm2 and subsequently annealed at 1200 °C for 1 min in N2 gas flow. For the Ti(50 nm)/Al(200 nm) contacts annealed at 550 and 600 °C, as Si ion dose is increased, the specific contact resistance is decreased with the Schottky barrier height of 0.27 eV. The Ti/Al contact annealed at 600 °C reveals the exteremly low contact resistance as low as 1.2 x 10–7 Ωcm2 for the Si ion dose of 5 x 1014/cm2. Ti/Al contact annealed above 700 °C shows Rc in the order of 10–6 Ωcm2 even though Si ion dose increases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Breakdown Voltage Enhancement of AlGaN/GaN High-Electron-Mobility Transistors via Selective-Area Growth for Ohmic Contacts over Ion Implantation

“…[1][2][3][4][5] Satoh et al demonstrated an ultralow-resistive Ohmic contact with a specific contact resistivity of 1.2 9 10 À7 X cm 2 . 6 Recht et al reported a contact resistance of 0.96 X mm for nonalloyed Ohmic contacts. 7 However, ion implantation generally requires high-energy radiation, which gives rise to damage at the surface and a dense network of defect clusters in the doped region.…”

Increase in net donor concentration due to introduction of donor-like defects by ultra-low-dose Si-ion implantation and subsequent annealing in homoepitaxial n-type GaN

“…Many researchers demonstrated that the contact resistance could be reduced by implanting Si ions into an area to form an electrode and annealing at relatively low temperatures between 900 °C and 1200 °C. 4,21,22) Irokawa et al estimated an activation ratio of 30% in a sample implanted with Si ions at a high dose of 2.5 × 10 14 cm −2 (corresponding to 6 × 10 18 cm −3 ) into a p-type layer under multiple energy conditions from 70 to 380 keV after annealing at 1200 °C; this value was obtained by dividing the net donor concentration (N D ) obtained from the C-V characteristics by the implanted Si concentration. 23) Various analyses such as Rutherford backscattering spectrometry, 4,24) X-ray diffraction, 4) positron annihilation spectroscopy (PAS) 25) and photoluminescence 26) have been also conducted to reveal the crystal quality of Si-implanted GaN.…”