ELECTRON-BEAM-INDUCED CURRENT IMAGING OF NEAR-CONTACT REGIONS IN SEMIINSULATING GAAS

Electron beam induced current (EBIC) in a scanning: electron microscop e has been used to image the internal electric field regions near impl anted contacts on semi-insulating GaA. Planar n(+)-i-p(+) structures w ere fabricated with interconnect distances ranging from 5 to 100 mu m. In cases where the diffusion length is short compared to the lengths of interest, the current collected is determined primarily by the loca l electric field profile. With no externally applied bias, we observe large current collection regions adjacent to the n(+) contact, extendi ng similar to 10-20 mu m into the bulk material. Two-dimensinal (2-D) imaging indicates that the regions are highly nonuniform. For small in tercontact distances, the contact-related fields, which are produced b y the diffusion and trapping of carriers from the contacts, can domina te the entire region. Changes in EBIC signal with the application of f orward or reverse bias are used to monitor the interaction of the zero bias field and the applied field. This approach provides a good estim ate of the field distributions in trap-dominated, high resistivity mat erials like semi-insulating GaAs, with a spatial resolution generally not obtained with other field imaging techniques.