SCANNED PHOTOLUMINESCENCE WITH HIGH SPATIAL-RESOLUTION IN SEMIINSULATING GAAS AND INP - ASPECTS OF SURFACE PASSIVATION AND PHOTODEGRADATION

Spatially resolved photoluminescence (SRPL) is a useful tool for evaluating the quality of semiconductors used within electronic and photonic devices. SRPL can be done in two ways; scanning with a focused laser beam or imaging with a Vidicon. Laser-scanned SRPL can provide both high spatial resolution and sensitivity in semi-insulating gallium arsenide, GaAs:SI, and iron-doped indium phosphide, InP:Fe. Imaging SRPL can provide rapid analysis at video rates. Video rate laser scanning with a 1-mu-m laser spot combines the advantages of both approaches. The contrast of SRPL scans in GaAs:SI wafers is improved by a plasma passivation treatment. Scans clearly reveal dislocated cell structures as bright bands, arsenic precipitates as dark dots and polishing damage such as scratches. Several techniques, including XPS, SIMS, TEM and DSL etching, have been used to analyse optical contrast and the passivation mechanism. SRPL scans must be done non-destructively to allow for subsequent device fabrication and yield analysis. Photodegradation is minimised if a pumping wavelength near 720 nm is selected. This observation is apparently due to a trade-off between surface recombination and photon recycling. The small dwell time during video scans assures a non-destructive measurement, leading to improved contrast relative to systems with longer dwell times. SRPL scans in InP:Fe reveal bright spot defects, without any need of passivation. Imaging SIMS, TEM and DSL etching have been used to analyse contrast in these scans. The bright spots are dislocations and iron phosphide precipitates that have gettered significant levels of silicon contamination.