Epilayer transfer for integration of III-V photodetectors onto a silicon platform using Au-Sn and Pd-Ge bonding
A novel process to bond InP-based, substrate-removed, vertical Schottky photodetectors to a commercially available silicon read-out integrated circuit is demonstrated as a new technique for optoelectronic hybridization. High-quality In(Al)GaAs epilayers were bonded to silicon substrates and patterned to form a 320×256 focal plane array to demonstrate this technique. The epilayers were joined to the silicon through a metal-metal bond of either Au-Sn or Ge-Pd. Scanning electron and optical microscopy revealed that the Au-Sn formed a eutectic (melting) bond, whereas the Ge-Pd formed a solid-state bond. Samples bonded with Ge-Pd exhibited superior performance and were easier to process than the Au-Sn samples. Using this bonding technique, samples with a dark current density of 595 pA/μm2 at -5 V and a peak responsivity of 0.21 A/W over λ = 0.8 to 1.5 μm were obtained. Bonded devices survived severe thermal cycling between 77 K and 373 K. The process described is uncomplicated and does not require any specialized equipment beyond that of a standard photolithography tool.