On-nanowire band-graded Si:Ge photodetectors

We report an on-nanowire (NW) band-graded photodetector, which pertains to the on-NW composition gradation from pure Si to pure Ge, Si1−xGex (0 ≤ x ≤ 1). By spatially and spectrally resolved photocurrent imaging on individual Si:Ge NWs, we demonstrated that the spectral on-set of interband photocarrier generation and its photocurrent amplitude is on-NW demultiflexed with respect to the relative Si:Ge composition in an individually addressable manner. It is also found that the on-NW variation in photoconductivity and gain by up to two orders of magnitude upon the visible light incidence. We attribute our observations to the photocarrier density modulation arising from both the continuously varying energy band-gap and surface trap-state density in the range of 1.5×10¹¹ cm⁻² and 4.3 × 10¹² cm⁻². Our on-NW band-modulated photodetectors suggest general implications for the heteroepitaxial integration of the broadband Si nanophotonic components.