Chip-scale short-wavelength infrared InGaAs microspectrometer based on a linear variable optical filter

Abstract

A miniaturized extended short-wavelength infrared (SWIR) InGaAs microspectrometer is fabricated and characterized. An In_0.83Ga_0.17As detector with a cutoff wavelength of 2.6 μm is successfully grown on metamorphic InAsP layers with a low surface roughness of 2.7 nm and a large strain relaxation of 96%. A wedge-shaped Si/SiO₂ Fabry–Perot (F–P) linear variable optical filter (LVOF), fabricated using a specially designed deposition process, shows that the transmission peaks of the F–P fundamental mode linearly increase with increasing SiO₂ cavity thickness. Similarly, a 256 × 1 InGaAs linear array detector integrated with Si/SiO₂ F–P LVOF detects the transmission spectra in the 1.6–2.6 μm range that linearly shifts towards longer wavelengths with a thicker cavity thickness. The dark current of the microspectrometer is dominated by the generation-recombination current at temperatures in the range of 180–300 K, caused by Shockley–Read–Hall recombination through mid-gap states in the depletion region. At 300 K, the microspectrometer exhibits a responsivity of 0.34 AW⁻¹ and a noise voltage of 76 nV Hz^−1/2, resulting in a specific detectivity of 6.3 × 10⁸ cm Hz^1/2 W⁻¹. We expect these single-chip SWIR micro spectrometers to be well-suited for applications in portable, wearable, or unmanned systems because of their compactness, robustness, and high spectral selectivity.