title: Direct heteroepitaxy of vertical InAs nanowires on Si substrates for broad band photovoltaics and photodetection.
abstract: Catalyst-free, direct heteroepitaxial growth of vertical InAs nanowires on Si(111) substrates was accomplished over a large area by metal-organic chemical vapor deposition. Nanowires showed very uniform diameters and a zinc blende crystal structure. The heterojunctions formed at the interface between the n-type InAs nanowires and the p-type Si substrate were exploited to fabricate vertical array photodiode devices which showed an excellent rectification ratio and low reverse leakage current. Temperature-dependent current transport across the heterojunctions was studied theoretically and experimentally in the dark and under AM 1.5 illumination. When operated in photovoltaic mode, the open-circuit voltage was found to increase linearly with decreasing temperature while the energy conversion efficiency changed nonmonotonically with a maximum of 2.5% at 110 K. Modeling of the nanowire/substrate heterojunctions showed good agreement with the experimental observations, and allowed determining the conduction band offset between the InAs nanowires and Si to be 0.10-0.15 eV. The external quantum efficiency and photoresponsivity profiles of the device showed a broad spectral response from the visible to the infrared region, indicating potential applications as a broad band photovoltaic cell or a visible-infrared dual-band photodetector.
authors.affiliation: Materials Science and Engineering, University of California, San Diego, La Jolla, California 92093-0418, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.forename: Xin-Yu
authors.initials: XY
authors.lastname: Bao
authors.forename: Cesare
authors.initials: C
authors.lastname: Soci
authors.forename: Yong
authors.initials: Y
authors.lastname: Ding
authors.forename: Zhong-Lin
authors.initials: ZL
authors.lastname: Wang
authors.forename: Deli
authors.initials: D
authors.lastname: Wang