Laser-based structure studies of silicon and gallium arsenide

Laser-based methods for studying silicon and gallium arsenide structure are nondestructive and capable of analyzing very small areas of a sample. These methods are used to monitor the effects of processing steps, determine the spatial uniformity of defects and doping across a wafer, and analyze devices. Two of the most widely used methods are photoluminescence measurements and Raman scattering. Photoluminescence measurements, used often in GaAs studies, collect radiation emitted from a sample irradiated with laser light of higher energy than the sample band-gap energy. This method identifies dopants and defects in the sample and assesses the relative amount of lattice damage caused by various processes. Raman scattering measurements collect laser radiation scattered by optical phonons in the sample. Widely used in Si studies, Raman scattering can show effects of stress, defects, crystallinity, surface morphology, and lattice temperature. Other methods include reflectivity, ellipsometry, and absorption measurements.