Effects of Metallization Thickness on the Thermal and Long-Term Stability of Pd/Sn Ohmic Contacts to n-GaAs

Abstract

The effects of metallization thickness on the thermal and long-term stability of Pd/Sn Ohmic contacts have been investigated. Metallization samples are furnace annealed at various temperatures and systematically characterized utilizing Scanning Electron Microscopy (SEM) and current-voltage (I- V) measurements. Contact resistivities, Q c , of the metallizations are measured using a conventional Transmission Line Model (cTLM) method. SEM is utilized to investigate the surface morphology of the contacts. Thermal stability analysis of the metallizations is carried out at 410 °C for 10 h, whereas long-term stability tests are performed at 300 °C for 400 h. After annealing at 410 °C for 10 h, Q c of the Pd(30 nm)/Sn(150 nm) metallization remains in the high 10 -5 Ω cm 2 range, whereas for the Pd(30 nm)/Sn(90 nm) and Pd(40 nm)/Sn(120 nm) contacts Q c values increase to the mid 10 -4 Ω cm 2 range under the same annealing conditions. The Pd(30 nm)/Sn(150 nm) metallization also displays improved long-term stability at 300 °C when compared to the Pd(30 nm)/ Sn(90 nm) and Pd(40 nm)/Sn(120 nm) contacts. The effects of a highly conductive overlayer, Au, on the thermal and long-term stability of Pd/Sn Ohmic contacts are also investigated.