Growth rate monitor for molecular beam epitaxy

摘要

A light source (20) with appropriate optics focusses light on the wafer surface (14) during deposition, while a nearby collector (30) is biased to collect photoemitted electrons from the growing surface. A pico ammeter (40) can be used to convert the small oscillatory current detected to a substantial voltage signal which can be recorded or processed by computer or other suitable device. The light must contain wavelengths at energies close to or greater than the energy of the photoemission threshold. The detected photoemitted electron signal has an oscillatory component occurring due to the growth of epitaxial layers. This oscillation has frequency 1/τ, where τ is the monolayer accumulation time.