PLASMA-ETCHING DAMAGE IN GAAS STUDIED BY RESONANT RAMAN-SCATTERING

We have used resonant Raman scattering by longitudinal optical (LO) phonons to study the effect of reactive ion etching (RIE) in a CHF3 plasma on n-type GaAs. Interference effects between dipole allowed and electric-field-induced forbidden LO phonon scattering have been exploited to distinguish between impurity-induced and electric-field-induced forbidden scattering. This allowed us to analyze both RIE-induced near-surface damage and resulting changes in the space-charge electric field as a function of the self-bias voltage applied in RIE. For bias voltages beyond 200 V a well-defined increase in defect concentration and consequently a reduction in crystalline perfection was observed. The surface electric field averaged over the probing depth of the Raman experiment shows an initial decrease followed by an increase with increasing bias voltage.