Single photon emitters in AlGaAs epilayers at liquid nitrogen temperature on Silicon substrates

One of the fundamental ingredients for quantum cryptography and quantum information applications is the fabrication of single and entangled photon emitters. Single photon emitter should produce exactly a single photon on demand, should work not only at cryogenic temperature and should be easy to produce and to integrate on existing electronic devices. In this work, we present the fabrication and characterization of single photon emission from high quality GaAs quantum dots (QDs) by droplet epitaxy (DE) and from impurity centers in AlGaAs layers grown on Si through a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD). The deposition of a thin Ge layer by LEPECVD and subsequent annealing cycles allow for the reduction of threading dislocation density down to few 107 cm-2. DE is an intrinsically low thermal budget technique, being performed at temperatures between 200 and 350 °C. This makes DE perfectly suited for the implementation of growth procedures compliant with back-end integration of III-V nanostructures on CMOS. GaAs QDs with a density of few 108 cm-2 and a mean height of 8 nm are fabricated by DE inside a Al0.3Ga0.7As barrier. 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. We also show that the epitaxial growth of thin layers of Al0.3Ga0.7As on GaAs buffer layers grown on Si and Ge substrates allows to obtain a single photon source by exploiting the strewn and unintentional contamination with defects of the Al0.3Ga0.7As. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in QDs, but their realization is by far much easier, since it does not require 3D nucleation or spatially selective doping. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements. In both cases (GaAs QDs by DE and impuritues in AlGaAs layer) it is clearly demonstrated 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.