Off axis holography of doped and intrinsic silicon nanowires: Interpretation and influence of fields in the vacuum

Intrinsic and axially modulated doped silicon nanowires (NWs) were studied by off-axis electron holography. Phase gradients in the vacuum were observed and compared to simulations of NWs with a varying charge density at the wire-oxide interface. It seems that intrinsic NWs are positively charged with a charge density around 2 × 10 10 e.c. (electron charges) cm −2 and axially modulated doped NWs (with n-doped regions) are negatively charged with a charge density around −1 × 10 12 e.c. cm −2 . Expected fringing fields around the doped regions are incidentally observed but smaller than predicted by simulations. The effect of the surface charge on the reference wave is evaluated, and should not modify the obtained phase image.