Out-of-plane strain induced non-thermal bandgap tuning of black phosphorus on-chip devices.

Black phosphorus (BP), a layered van der Waals material with a direct bandgap and broad spectral tunability, offers new opportunities for developing advanced on-chip photonic architectures and operating mechanisms. In contrast to the widely studied in-plane strain tuning (typically requiring soft substrates), this work explores, through numerical simulation, out-of-plane strain as a means of spectral control compatible with rigid integrated platforms. We demonstrate that compressive out-of-plane strain reduces the bandgap of BP in proportion to the geometric compression in BP thickness, and thus, a -3.0% strain induces a synchronous redshift of over 100 nm in both the electroluminescence and the cavity resonance wavelengths. This cooperative tuning behavior is particularly significant for on-chip coherent emitters, enabling nearly constant output intensity across the entire tuning range. Moreover, this non-thermal tuning approach substantially alleviates thermal management challenges in highly integrated silicon photonic circuits.