On-chip optical spectrometer based on GaN wavelength-selective nanostructural absorbers

Abstract

A spectrometer concept based on wavelength-selective semiconductor photodiodes is proposed and demonstrated. The absorption properties of individual photodiodes were tuned via local strain engineering in nanostructured InGaN/GaN. By varying the diameters of individual nanopillars, the cutoff wavelengths of absorption were varied across the chip. The intrinsic wavelength selectivity is insensitive to the incident angle of light. The top-down fabrication process shown in this work is also compatible with scalable manufacturing. A proof-of-concept spectrometer was demonstrated based on 14 photodiodes, without any external optics or spectral filtering components, in the wavelength range of 450-590 nm. Using a non-negative least squares algorithm enhanced by orthogonal matching pursuit, the spectrum of a test light source was reconstructed.