Case Studies 02

Photo-Carrier Radiometry (PCR)

Diffusion Wave Technologies’s Photo-Carrier Radiometry (PCR) technology uses laser radiation of high enough energy to free up electrical carriers (electrons and/or holes) from their atoms in semiconductor silicon. These free electrons or holes roam around the Si wafer crystal (diffuse) for a specified amount of time (usually microseconds to milliseconds) and then fall back into lower-energy empty states which can accommodate them (a process called “recombination”), thereby losing their excess energy by emitting an infrared photon. These photons are collected by spectrally matched external optics and detectors, thus monitoring the amount of infrared emissions by the wafer (radiometry). PCR completely obliterates the thermal infrared emission band (8-12 um), unlike the known photo-thermal signal types, which invariably contain combinations of carrier-wave and thermal-wave infrared emissions due to the concurrent lattice absorption of the incident beam and non-radiative heating.