Influence of the electrical contact on the reliability of InP-based ridge waveguide distributed feedback semiconductor diode lasers for telecommunications applications

The design of a ridge waveguide semiconductor diode laser requires the definition of a high-quality metal contact to a p-type semiconductor that has been patterned to form the laser ridge. In the InGaAsP material system, Zn-doped, p-InGaAs is used as the contact layer. An evaporated multilayer metal stack consisting of Ti, Pt, and Au is alloyed to the InGaAs to form a stable ohmic contact with good adhesion. The alloying process is an intermixing of the Ti and As. Pt is not reactive during the alloying process and acts as a diffusion barrier. In this work, the Pt and Ti layer thicknesses were varied to improve the laser reliability. The layer thicknesses were optimized with the goal of producing a minimum stress in the laser active region. A preliminary study of completely processed lasers indicates that the laser reliability is significantly influenced by the changes to the stress induced in the device by the p-contact metal stack. Further work is required to establish the relationship between the stress in the active region of the device, and the stress contribution from the p-contact metal stack. (C) 2004 American Vacuum Society.