19 April 1996 Fast MSM modulators based on the two-dimensional Franz-Keldysh effect in MQW structures
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Abstract
We report on a novel electro-optic modulator structure based on the two-dimensional Franz- Keldysh effect (2D-FKE) in multiple quantum well (MQW) structures. Due to the increased electron-hole interaction in these quasi-two-dimensional systems, strong excitonic resonances are observed even at room temperature. If an electric field is applied parallel to the layers of a MQW structure, very low electric fields (10 - 30 kV/cm) are sufficient to cause field ionization of the excitons, because of their weak in-plane confinement. Large absorption changes as high as 7000 cm-1 with field changes of only 30 kV/cm have been observed in GaAs/AlGaAs-MQWs. In addition, an increase of the absorption below and oscillations of the absorption coefficient above each subband transition are obtained due to the two-dimensional Franz-Keldysh effect. These features have been applied in our novel electro- optic modulator structure. Using interdigitated metal-semiconductor-metal (MSM) contacts, high in-plane electric fields can be generated with moderate voltages. Furthermore the low capacitance of these MSM structures is particularly favorable for high speed applications. In a MSM-modulator structure, consisting of 75 GaAs/AlGaAs quantum wells with a distributed Bragg-reflector (DBR) below the MQW-layers, a maximum contrast ratio of 5:1 without using any cavity effects has been achieved with a voltage swing of 20 V.
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Michael Kneissl, Michael Kneissl, Peter Kiesel, Peter Kiesel, Norbert Linder, Norbert Linder, Angela Thranhardt, Angela Thranhardt, Helmut Grothe, Helmut Grothe, Gottfried H. Doehler, Gottfried H. Doehler, } "Fast MSM modulators based on the two-dimensional Franz-Keldysh effect in MQW structures", Proc. SPIE 2694, Quantum Well and Superlattice Physics VI, (19 April 1996); doi: 10.1117/12.238397; https://doi.org/10.1117/12.238397
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