Modulation Spectroscopy As A Technique For Semiconductor Characterization

In modulation spectroscopy the optical spectra of a solid is modified in some manner by the periodic variation of the measurement condition. This modulated perturbation gives rise to sharp, differential-like optical features in the region of photon energies where optical excitation processes occur. Changes in reflectance or transmittance as small as 10-6 - 10-7 can be observed using phase-sensitive detection. The extensive fundamental experimental and theoretical work done in this area during the past 15 years has provided the necessary framework to develop the technique into a powerful tool for materials, device and processing characterization. In this paper we review a number of the applica-tions of modulation spectroscopy including determination of topographical variations in composition and carrier concentration, the nature of potentials and strains at hetero-junction interfaces, properties of the space-charge region including the semiconductor/ electrolyte interface, ion-implanted (including laser-annealed) semiconductors polariza-tion properties of ferroelectric materials, etc.