Abstract

We report the first measurement of the quadratic Stark shift of the bound exciton ground state (D°X) in the direct gap CdS semiconductor. The exciton is confined in three dimensions by the potential of a neutral donor (Li or Na interstitials) which restricts the exciton motion over dimensions of order of the free exciton Bohr radius (30 Å). Optical transmission measurements with a single mode dye laser reveal a very narrow linewidth (8-10 GHz) which implies a very well defined and reproducible potential well. This is in sharp contrast to previous realizations of three dimensional excitonic confinement where linewidths about 1000 times larger are commonly observed because of the large variations of the potential dimensions. At an electric field of 2.5 x 10⁴ V/cm, a shift of the bound exciton resonance as large as its half-width at half-height is observed without any appreciable broadening of the resonance. The bound exciton shift is about 25 times smaller than the free exciton Stark shift measured in the same experimental conditions.

© 1988 Optical Society of America