Selective deposition of ohmic contacts to p-InGaAs by electroless plating

A three-layer PdRuAu electrolessly deposited ohmic contact to p-InGaAs, suitable for use in a self-aligned process, is presented. Cross-sectional transmission electron microscopy shows that the electrolessly plated metal layers are dense with a thin uniform reaction between the Pd and InGaAs. This contact metallization remains shallow and electrically stable even after aging for 4 h at 250°C. An average specific contact resistance of (1.6±0.6) × 10-6 Ω cm2 was obtained for as-deposited contacts with an HCl surface treatment. When a UV ozone and N H4 OH surface treatment was used, specific contact resistances as low as (2.1±0.9) × 10-7 Ω cm2 were obtained.