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.

In this paper, a spectrometer design enabling an ultrathin form factor is proposed. Local strain engineering in group III-nitride semiconductor nanostructured light-absorbing elements enables the integration of a large number of photodetectors on the chip exhibiting different absorption cut-off wavelengths. The introduction of a simple cone-shaped back-reflector at the bottom side of the substrate enables a high light-harvesting efficiency design, which also improves the accuracy of spectral reconstruction. The cone-shaped back-reflector can be readily fabricated using mature patterned sapphire substrate processes. Our design was validated via numerical simulations with experimentally measured photodetector responsivities as the input. A light-harvesting efficiency as high as 60% was achieved with five InGaN/GaN multiple quantum wells for the visible wavelengths.

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AlxGa1–xN/GaN disk-in-wire polar nanostructures were fabricated, and their optical properties were studied. Wavelength tuning was observed by locally controlling the strain in each nanopillar via its diameter. The measured wavelength shift was in an excellent agreement with a one-dimensional strain relaxation model considering only the elastic and piezoelectric properties of the material. The inhomogeneous broadening decreases and internal quantum efficiency increases with a decreasing nanopillar diameter. The potential extension of strain-induced wavelength tuning across ultraviolet through near infrared was also discussed.