Electron beam induced current imaging of near-contact regions in semi-insulating GaAs

Electron beam induced current (EBIC) in a scanning electron microscope has been used to image the internal electric field regions near implanted contacts on semi-insulating GaAs. Planar n⁺-i-p⁺ structures were fabricated with intercontact distances ranging from 5 to 100 μm. In cases where the diffusion length is short compared to the lengths of interest, the current collected is determined primarily by the local electric field profile. With no externally applied bias, we observe large current collection regions adjacent to the n⁺ contact, extending ~10-20 μm into the bulk material. Two-dimensional (2-D) imaging indicates that the regions are highly nonuniform. For small intercontact distances, the contact-related fields, which are produced by the diffusion and trapping of carriers from the contacts, can dominate the entire region. Changes in EBIC signal with the application of forward or reverse bias are used to monitor the interaction of the zero bias field and the applied field. This approach provides a good estimate of the field distributions in trap-dominated, high resistivity materials like semi-insulating GaAs, with a spatial resolution generally not obtained with other field imaging techniques