  Electronic devices are extremely sensitive to defects in their constituent
semiconductors, but locating electronic point defects in bulk semiconductors
has previously been impossible. Here we apply scanning transmission electron
microscopy (STEM) electron beam-induced current (EBIC) imaging to map
electronic defects in a GaAs nanowire Schottky diode. Imaging with a
non-damaging 80 or 200 kV STEM acceleration potential reveals a
minority-carrier diffusion length that decreases near the surface of the
hexagonal nanowire, thereby demonstrating that the device's charge collection
efficiency (CCE) is limited by surface defects. Imaging with a 300 keV STEM
beam introduces vacancy-interstitial (VI, or Frenkel) defects in the GaAs that
increase carrier recombination and reduce the CCE of the diode. We create,
locate, and characterize a single insertion event, determining that a defect
inserted 7 nm from the Schottky interface broadly reduces the CCE by 10% across
the entire nanowire device. Variable-energy STEM EBIC imaging thus allows both
benign mapping and pinpoint modification of a device's e-h recombination
landscape, enabling controlled experiments that illuminate the impact of both
extended (1D and 2D) and point (0D) defects on semiconductor device
performance.
