Design of high performance Graphene/Silicon photodetectors

A thin layer of graphene on a light absorbing substrate (e.g., Silicon (Si)) is capable of an ultrahigh sensitivity for light detection. Demonstrated in both 2 terminal (diode) and 3 terminal (MOSFET) configurations, graphene on Si devices can outperform conventional photodetectors in detecting weak light signals. High photo responsivity in graphene on Si originates from substrate a combined effect of (i) graphene doping due to photo generated carrier injection from substrate, and, (ii) high carrier mobility of graphene which enable a large quantum gain. Here we explore the design parameters that affect the photo induced graphene doping using self-consistent numerical simulations. We note that photo response can be substantially improved when substrate carriers have low mobility and high lifetime. The apparently counter-intuitive dependence of photo response on substrate's mobility is physically explained.