GaAs single photon emitters at liquid nitrogen temperature grown by droplet epitaxy on Si substrate

The integration of III-V nanostructures on silicon would allow to combine the high performance of quantum photonic devices and of CMOS circuitry on Si. In this work, we present the first demonstration of single photon emission from high quality GaAs quantum dots (QDs) grown by droplet epitaxy on Si substrates using a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD). Droplet epitaxy allows for the separate control of the QD size and density, and provides the possibility to fabricate different classes of quantum nanostructures with tailored wavefunctions and electronic levels. Droplet epitaxy is also an intrinsically low thermal budget growth, being performed at temperatures between 200 and 350 C. This makes droplet epitaxy perfectly suited for the realization of growth procedures compatible with back-end integration of III-V nanostructures on CMOS. The deposition of a thin Ge layer by LEPECVD allows for the reduction of threading dislocation density down to few 10^-7 cm . GaAs QDs with a density of few 10 cm and a mean height of 8 nm are fabricated by droplet epitaxy inside a Al0.30Ga0.70 As barrier. Two annealing procedure are performed, the first one in chamber right after the quantum dots growth to desorb As excess while the second one (performed in a rapid thermal annealing system) improves crystal quality. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. The optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates, clearly demonstrating a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology.