Abstract

The optical absorption of semiconductors near the band gap is sensitive to the applied electric field. The Franz-Keldysh (F-K) effect results in increased optical absorption below the band gap when a field is applied. Although the F-K electroabsorption has been applied to optical modulators¹ and has been shown to exhibit a response time of <1 ps in GaAs,² excitonic effects have not been investigated or utilized in this time scale. Excitonic electroabsorption has recently been investigated in the GaAs/AIGaAs system at speeds up to 30 ps.³ Because excitonic electroabsorption offers much larger modulation and higher sensitivity than the F-K effect, it is interesting to consider whether the excitonic enhancement provides a physical limit to the modulation speed. Of course, the existence of strong exciton resonances at room temperature in GaAs MQWs⁴ would make such devices practical. We report the first subpicosecond investigation of excitonic electroabsorption. We apply electric fields parallel to the layers in this experiment.

© 1986 Optical Society of America