Silicon microsphere photodiodes constitute optoelectronic devices able to provide resonance-enhanced photocurrent not only in the visible but also in the near infrared range by virtue of their associated Mie resonances. They are synthesized by means of a bottom-up process that allows obtaining thousand of devices in a single batch. The microspheres have revealed an internal structural configuration that strongly influences the photocurrent response, thus providing an additional degree of freedom for tuning the properties of the photodiodes. Here, devices with a particular internal configuration consisting of a high porous core, a much less porous surrounding layer and a thin non-porous shell, have been studied. They yield comb like peaked photocurrent spectra that have been fitted to a Mie type model. In addition, net energy conversion at 1500 nm has been demonstrated.

Fenollosa, R., & Garín, M. (2022). Multilayer porous silicon spherical mie resonator photodiodes with comb-like spectral response in the near infrared region. Materials Science in Semiconductor Processing, 150. https://doi.org/10.1016/j.mssp.2022.106972

 

Fig. 4. a HRTEM image of the internal surface of a crystallized silicon microsphere. Different regions characterized by distinct pore sizes: P1, P2, and P3, as well as the non-porous shell (NPS) are indicated. b Zoomed area of a for better visualizing the transition between P1 and P2. c and d Higher-magnification images illustrating the transition between P2–P3 and P3-NPS, respectively. The scale bars correspond to 1 μm (a), 100 nm (b), 50 nm (c), and 20 nm (d). Reproduced from Ref. [21] with permission.

4. Conclusions

Photodiodes based on silicon microspheres with an internal porous multilayer structure can absorb light and produce photocurrent and net energy conversion in the near infrared, below the silicon bandgap, at wavelengths of up to 2000 nm. The internal structure of the microspheres as well as the light scattering by the pores strongly influences the photocurrent giving rise, for some particular configurations, to comb like spectra. This provides another degree of freedom that can be used for engineering NIR optoelectronic devices based completely on silicon.