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19 April 1996 Fast MSM modulators based on the two-dimensional Franz-Keldysh effect in MQW structures
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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.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael Kneissl, Peter Kiesel, Norbert Linder, Angela Thranhardt, Helmut Grothe, and 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);

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