Pt/Ti/p-InGaAsP nonalloyed ohmic contact formed by rapid thermal processing

Abstract

Nonalloyed ohmic contacts of Pt/Ti to 5×10¹⁸ cm⁻³ doped p‐InGaAsP (λ_g =1.3 μm) have been fabricated by rapid thermal processing of sputtered and e‐gun‐deposited metallizations. While the former as‐deposited had a rectifying characteristic, the latter showed ohmic behavior prior to any heat treatment, with a specific contact resistance of 4×10⁻³ Ω cm². Rapid thermal processing at temperatures higher than 400 °C caused the formation of ohmic contacts for the sputtered metals also, but with the evaporated metals producing slightly lower contact resistance. The lowest specific contact resistance values of 3.6–5.5×10⁻⁴ Ω cm² for evaporated and sputtered metallizations, respectively, were achieved in both cases as a result of heating at 450 °C for 30 s. These heating conditions produced only a limited reaction at the Ti/InGaAsP interface, which was sharper for the e‐gun‐deposited contact, but had a significant effect on the stresses in the Ti/Pt bilayer. In both the sputtered and electron gun evaporated samples, the stresses were inverted from tensile as‐deposited to compressive with values of 2.4×10⁹ and 1.0×10⁹ dyn cm⁻², respectively, as a result of the heat treatment.