Fig. 1: Spatially confined hot carrier dynamics in semiconductors.

a In semiconductor-based optoelectronic devices, the cooling process of photoexcited hot carriers is unrestricted, and typically occurs within a few picoseconds. Hot-carrier energy loss rate is dominated by phonon emission, and intensifies with higher photon energy. This leads to rapid energy dissipation, a decline in spectral responsivity, and reduced external quantum efficiency (EQE) at shorter wavelengths for optoelectronic devices without external voltage bias. b To effectively manage the hot carrier relaxation, the spatially confined structure amplifies the local phonon bottleneck effect and prolongs the carrier diffusion lifetime, manifested as the slow decay of normalized transient reflectivity (ΔR/R). The enhanced EQE fundamentally results from the competition between hot carrier relaxation dynamics and carrier collection efficiency. Particularly in the short wavelength range, thermalized cold carriers participate more effectively in the collection process. Together, these effects lead to a significant enhancement in spectral responsivity.