photocontact

Photocontact is a term used in more than one field, referring to light-related contact phenomena in both photography and electronics.

In photography and printmaking, a photocontact, or contact print, is a print produced by placing a photographic negative directly onto a light-sensitive surface and exposing it to light. Because the negative is in direct contact with the paper or emulsion, the resulting image is the same size as the negative. This simple method preserves the framing and tonal range of the original and is commonly used for proof sheets, portfolios, or archival reproductions. The process can utilize traditional printing-out papers or modern papers, and the resulting image can be positive or negative depending on materials and chemistry. Historically, contact printing played a central role in darkroom workflows, though digital workflows have largely supplanted it for everyday production.

In electronics and materials science, photocontact denotes an electrical contact whose conduction is activated or enhanced by illumination. When photons generate electron–hole pairs near a metal–semiconductor interface or within a semiconductor, the resulting carriers can reduce a barrier or resistance, producing a measurable photocurrent under bias. Photocontact techniques are used to characterize interfaces, estimate barrier heights and work function differences, and study carrier diffusion lengths. They appear in studies of Schottky junctions, photoresponse measurements of detectors, and light-assisted contact formation in microfabricated devices. The precise interpretation of photocontact depends on the materials system and experimental setup, and it is distinguished from purely dark-contact measurements.

In summary, photocontact describes light-enabled contact phenomena, with distinct meanings in photographic printing and in light-induced electrical contacts.