Metal Contacts for the Hybrid Silican Laser

Standard copper cables are overloaded by current communication rates.  Fiber optic cables, which transmit information using light, can transfer data faster and more efficiently.  The light sources for these cables, lasers made entirely from III-V materials such as Indium Phosphide (InP) and Indium Gallium Arsenide (InGaAs) are too expensive for widespread use.  A laser made partially from Silicon would dramatically bring down cost, but this introduces a problem of what type of metal contact can be used to allow current flow through the laser.  Gold, an important part of most contacts to III-V materials, is incompatible with silicon fabrication facilities.  Alternative gold-free contact stacks of Ti/W/Al, and Pd/Ge/Pd/W/Al (with varying Pd:Ge ratios) were deposited on wafers of both InP and InGaAs and annealed at temperatures of 350°, 450°, and 550°C for 30 seconds each.  Specific contact resistances, which we aim to minimize, were calculated from four-point probe measurements.  So far, the best specific resistance values have been on the order of 10-7 Ω-cm2 for Pd/Ge/Pd/W/Al contacts (with a Pd:Ge ratio of 0.5) on InP, annealed at 350°C.  By the end of the project, we hope to find a contact that will work equally well on both InP and InGaAs, to simplify manufacturing.