All-Silicon spherical-Mie-resonator photodiode with spectral response in the infrared region

Abstract

Single-junction photovoltaic devices suffer from intrinsic obstacles limiting their efficiency to a top value dictated by the well-known Shockley¿Queisser (SQ) limit [1]. The development of photodiode devices on micro and nanophotonic structures has opened new possibilities over the standard technology. The impinging light is strongly confined inside those photonic struc-tures, enhancing optical absorption and photocarrier generation, as it has been reported for planar optical cavities and, more recently, for nanowire resonators [2,3]. The most fundamen-tal limitation is given by the energy bandgap of the semiconductor, which determines the min-imum energy of photons that can be converted into electron-hole pairs. In the case of silicon a large percentage of infrared sunlight, with energy value below the fundamental absorption edge of silicon, is still useless. Here we show the first example of a photodiode developed on a micrometer size silicon spherical cavity whose photocurrent shows the Mie modes of a classi-cal spherical resonator. The long dwell time of resonating photons enhances the absorption efficiency of photons. Also the photocurrent response shows very rich spectra with plenty of high-Q resonant peaks in a similar manner as the scattering spectra of high order whispering gallery modes (WGMs) of spherical microcavities. Also, as a consequence of the enhanced resonant absorption, the photocurrent response extends far below the bandgap of crystalline silicon [4]. It opens the door for developing a new generation of solar cells and photodetectors that may harvest infrared light more efficiently than silicon based photovoltaic devices.