Fig. 1: Schematic and electric properties of the p-graded-n junction spectrometer.

a Schematic diagram of a p-graded-n junction spectrometer. The Al composition of the n-AlGaAs layer is graded from 0 to 0.5 along the growth direction. b Device working principle. As the applied reverse bias increases, the depletion region extends downwards, gradually turning on the new absorption regions with longer cut-off wavelength. c, d Band diagram of the p-graded-n junction spectrometer under low reverse bias (up) and high reverse bias. e Dark current density and photo current density of the detector. f Measured responsivity of the detector from 400 nm to 900 nm. Lines are the responsivity of the detector under different bias ranging from 0 V to −10 V. g Responsivity versus reverse bias and wavelength. The detector exhibits a longer wavelength response as the reverse bias voltage increases.