Local Band‐Profile Control Unlocks Multipeak Spectral Reconstruction in a Single Photodetector

Accurate spectral analysis in compact platforms is essential for portable sensing, integrated photonics, and on‐chip materials characterization. Single‐detector computational spectrometers offer an appealing route toward extreme miniaturization, but their performance is fundamentally constrained by the intrinsic structure of bias‐dependent responsivity curves: these responses evolve smoothly and non‐orthogonally with wavelength, producing highly correlated photocurrent patterns that collapse the effective rank of the responsivity matrix. Such low‐rank encoding leads to ill‐conditioned inverse problems, making the reconstruction of multi‐peak or densely spaced spectra particularly fragile to noise and device imperfections. Here, we overcome this long‐standing limitation by introducing gate‐tunable band‐profile modulation in an in‐plane dual‐bottom‐gate black phosphorus photodetector. Independent gate control forms a reconfigurable local potential barrier that generates strongly wavelength‐dependent photocurrent maps, substantially enhancing spectral discriminability and improving the effective rank and numerical conditioning of the responsivity matrix. Leveraging this encoding mechanism, a single detector enables high‐accuracy single‐peak identification over a 500‐nm near‐infrared band and reliable one‐to‐eight‐peak reconstruction within a calibrated window. We further demonstrate robust graphene layer‐number identification, including regimes where Raman spectroscopy becomes ambiguous. This work establishes band‐profile engineering as a general device‐level strategy for advancing single‐detector computational spectrometers and enabling compact, high‐fidelity spectral sensing.