Abstract

Quantum well systems, where electrons and holes are confined in thin (e.g., 100-Å) layers of a narrow band gap semiconductor (e.g., GaAs) by the adjacent wider band gap semiconductor layers (e.g., GaAIAs), show several interesting optical effects. In addition to making exciton absorption resonance resolvable at room temperature, the confinement results in the quantum-confined Stark effect (QCSE)¹; with electric fields perpendicular to the layers of the material, the excitonic absorption shifts by large amounts (e.g., 40 meV). This effect enables high-speed modulators of micron thickness to be made.² It can be explained as a Stark shift of the exciton energy in which the confinement inhibits the field ionization (which normally would destroy the resonance). Shifts as large as four times the binding energy can be seen at fields corresponding to 200 times the classical ionization field. The structures can also simultaneously operate as photodetectors with photocurrent proportional to absorbed power. Since absorbed power depends on voltage (field) through the QCSE, a simple electronic circuit (e.g., a resistor and bias supply) gives optoelectronic feedback which is the principle of the self-electrooptic effect device (SEED).³ Positive feedback gives optical bistability, while with negative feedback, linearized modulation and optical level shifting are possible. These devices are compatible with diode lasers and semiconductor electronics in wavelengths, power levels, voltages, materials, and fabrication, and offer very low energy operation (e.g., –10 fJ/ square micron).

© 1985 Optical Society of America