Aluminum Oxide Passivating Tunneling Interlayers for Molybdenum Oxide Hole-Selective Contacts

Aluminum oxide thin films fabricated via atomic layer deposition are introduced as passivating tunneling interlayers between hole-selective molybdenum oxide contacts and silicon absorbers. Surface recombination velocity and specific contact resistivity are reported as a function of Al2O3 thickness. The effects of substrate chemical pretreatment, the thermal history of the Al2O3 layers prior to MoOx deposition, and the thermal history of the completed Al2O3/MoOx stacks were also investigated. When an SiOx/Al2O3 passivating stack was incorporated and the completed test structure was annealed at 200 degrees C, the observed recombination velocities were reduced from similar to 10 000 cm/s for an unpassivated (initially hydrogen-terminated) Si/MoOx direct contact to similar to 500 cm/s, while maintaining a contact resistivity at or below 0.1 omega center dot cm(2). The data demonstrate the capability of ultrathin Al2O3 to improve Si/MoOx contact properties and may be of interest in the design of future Si heterojunctions.