On‐Chip Measurement of Photoluminescence with High Sensitivity Monolithic Spectrometer

Abstract Monolithic spectrometer is exceptionally attractive to enable compact, low‐cost spectroscopy for portable sensing and lab‐on‐a‐chip functionality. Unfortunately, simple down‐scaling of the microspectrometer size to the chip‐scale severely weakens light–matter interactions and degrades the sensor performance to unacceptable level. Unlike other state‐of‐the‐art miniature spectral splitting filters or photonic structures, bandgap‐graded nanowire strongly enhances the light‐matter interaction, which is a highly demanded yet unfulfilled feature for high‐precision on‐chip sensing. Here, on‐chip measurement of photoluminescence by a monolithic spectrometer made of a single composition‐graded CdS_xSe_1–x nanowire is reported. The nanowire is engineered to a waveguide‐mode‐operated, dispersive photodiode array. It works as a monolithic spectrometer chip with strong light–matter interaction and superior noise figure. On‐chip measurement of single‐point photoluminescence signals with 10¹³ Jones room‐temperature detectivity and 5 nm spectral resolution is illustrated. This demonstration of a compact, low‐cost, and high‐performance miniature spectrometer marks a major step towards on‐chip spectroscopy for fine resolution and sensitive detection.