High-performance infrared light trapping in nano-needle structured p+ SnOx ( x ≤ 1)/thin film n-Ge photodiodes on Si

We report nano-needle structured conductive SnOx (x <= 1) as a self-assembled electrode for high-efficiency light trapping in thin-film infrared (IR) photonic devices, benefiting from the high scattering efficiency, high density, and low IR loss of the nano-needles. We demonstrate a 2.2x responsivity enhancement for a 1.5-mu m-thick Ge absorber in a nano-needled p(+) SnOx/n-Ge photodiode on Si at lambda = 1580 nm, in good agreement with theoretical calculation of 2.3x enhancement assuming no IR loss in the nano-needles. Such low-loss light trapping can potentially enable 15-30x absorption enhancement at lambda = 1600-1650 nm in the Ge layer when integrated with a perfect rear reflector. (C) 2015 Optical Society of America