BRIGHT VISIBLE PHOTOLUMINESCENCE OF SPARK-PROCESSED GE, GAAS, AND SI

High-frequency spark discharges were applied to single-crystalline waf ers of Ge, GaAs, and Si. The spark-processed (sp-) samples were charac terized by photoluminescence (PL) and Raman measurements. Strong and s table luminescence with wavelengths centered at 416 and 525 nm was obs erved in sp-Ge and sp-Si layers, respectively, when excited with a 325 nm laser beam. A considerable blue shift of the PL (compared to the u nsparked specimen) was also detected for sp-GaAs with an average peak wavelength around 500 nm. The Raman Shifts of the spark-processed mate rials indicate that nanocrystals were formed, having diameters of 3.5- 4 nm for Si and about 6 nm for Ge. A correlation between the PL wavele ngths, the nanocrystal sizes, and the different semiconductor material s has been established based on the effective-mass approximation. Maki ng use of this model the nanocrystallite sizes have been found to rang e between similar to 3 nm for Si and similar to 5 nm for Ge. The relat ed wavelengths for optical transitions confirm the PL results. The fin dings support the quantum confinement model.