Aloof Electron Probing of In-Plane Surface Photovoltaic Charge Distributions on GaAs Surfaces

The motion of free electrons moving parallel and above a semiconductor surface can be influenced by shining a laser light onto the surface. Here we report strong deflection of aloof electrons by an undoped GaAs surface illuminated with a 633 nm laser. The deflecting electric field from the surface photovoltaic charges extends 100 μm into the vacuum. As surface photovoltage (SPV) is sensitive to the electronic states of the GaAs surface, the aloof electron beam serves as a probe for SPV charge dynamics on the mesoscopic length scale. The observed in-plane SPV charge distribution persists beyond 1 second after the laser beam is blocked. Our work suggests the possibility of writing designed 2D charge patterns on semiconductor surfaces with a scanning laser beam, providing unusual flexibility for electron beam manipulation.