Scanned photoluminescence of semiconductors
Photoluminescence (PL) scanning is used to assess a number of material- or process-related concerns in semiconductors. Since it is a non-destructive, non-contact technique, it can be used at any stage of the fabrication process. It was first used to examine dislocation distributions in GaAs and its value was well established when good correlations were found between PL contrast and device electrical properties. With the advent of whole ingot annealing it became possible to determine the 'quality' of the annealing step by the residual PL contrast across the wafer; this too correlated with electrical properties. The theory of PL output efficiency at room temperature was developed and this efficiency was shown to depend most on the surface recombination velocity. PL scans thus became valuable for looking at surface passivation effects and the effects of chemical treatment. The theory was extended to explain the phenomenon of PL decay as a function of atmosphere, surface treatment and passivation.