Abstract

We report optical rectification from the surface depletion layer of a semiconductor. As an ultrafast laser pulse illuminates a bare semiconductor surface, photons are absorbed, creating electron-hole pairs. The free carriers are swept cross the depletion layer and form a photocurrent driven by the internal field. This transient current in the depletion layer radiates diffraction-limited electromagnetic waves. The radiation field with a bandwidth from DC to 2 THz does not depend on the long carrier lifetime. The forward and backward rectified fields satisfy a generalized Fresnel's law. To generate a electrical beam with a terahertz bandwidth, in contrast with photoconducting transmitter, a semiconductor wafer does not require radiation-damage, antenna fabrication and external bias. In addition, from the analysis of measured waveforms of the rectified field, strength of the build-in static field and depletion width at the surfaces and interfaces can be estimated with a noncontact approach. The rectified fields from several III-V, II-VI and group IV semiconductors have been examined.

© 1989 Optical Society of America