Abstract
The broadening of excitonic absorption lines can be the dominant mechanism for optical nonlinearities in semiconductors, for example, at low intensities in low-temperature CdS.1 On the other hand, for charge-transport-enhanced optical nonlinearities,2 exciton broadening typically makes a small, contribution. In hereto n-i-p-i structures containing conventional multiple quantum wells, for example, optical nonlinearities arise when the quantum-confined Stark effect: (primarily a red shift of exciton lines in an electric field) is cancelled by photocharge. Here we report studies of optical nonlinearity in a hetero n-i-p-i material with coupled quantum wells, for which exciton broadening is the dominant effect. In contrast to the quantum-confined Stark effect, the broadening discussed here occurs when electric fields decrease, so optical excitation of this n-i-p-i causes an increase in absorption just below the absorption edge. In this sense, the material is similar in its optical response to self-electro-optic devices based on a blue shift of the absorption edge of a superlattice in an electric field.3
© 1991 Optical Society of America
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