Investigation of spatial distribution of photocurrent in the plane of a Si $p$–$n$ photodiode with GeSi nanoislands by scanning near-field optical microscopy

The spatial distribution of photocurrent in the plane of a Si-based $p^+$–$n$ junction with embedded self-assembled Ge$_{x}$Si$_{1-x}$ ($x\approx$ 0.35) nanoislands is studied by scanning near-field optical microscopy with local photoexcitation by a microscope probe at an emission wavelength of 1310 nm (larger than the intrinsicphotosensitivity red edge for Si). Inhomogeneities related to interband optical absorption in separate GeSi nanoislands are observed in the photocurrent images (maps of the spatial distribution of the photocurrent in the input-window plane of the $p^+$–$n$ photodiodes). The results of this study demonstrate the possibility of visualizing individual GeSi nanoislands in images of the photocurrent with a spatial resolution of $\sim$100 nm.