Electro-Optic Effects in Multiple Quantum Well GaAs/AlGaAs Stripe Waveguides

Jennings, John Andrew (1990) Electro-Optic Effects in Multiple Quantum Well GaAs/AlGaAs Stripe Waveguides. PhD thesis, University of Glasgow.

Abstract

The quantum confined Stark effect (QCSE) has been studied in multiple quantum well GaAs/AlGaAs, with a large electric field (10 5V/cm) applied in a direction normal to the plane of the wells, concentrating on the associated electro-absorption and electro-optic effects at wavelengths close to the excitonic absorption edge. The electrooptic effect has been resolved into two components: the linear electro-optic (LEO) effect and electro-refraction which manifests as a quadratic electrooptic (QEO). The LEO has been shown to be quantitatively very similar to bulk GaAs. The LEO coefficient r63= -1.75x10-1 2cm/V in MQW with 8.5nm wide wells and barriers for light polarised parallel to the plane of the wells and shows no wavelength dependance for photon energies in the range 105meV to 34meV from the excitonic absorption edge. The effect is absent for light polarised perpendicular to the plane of the wells. The QEO, however, is seen to be very different to that observed in bulk GaAs, with the QEO dominating the electro-optic effect. There is an increase in the QEO coefficient s33 of two orders of magnitude, from 1x10-20m2/V2 to 140x10-20m2/V2 over the range of wavelengths from 105meV to 34meV below the lowest energy exciton. Below the band gap, the QEO is dominated by the Stark shift of the lowest energy exciton. Stripe waveguide modulator devices in MQW GaAs/AlGaAs material compatible with integration of diode lasers have been fabricated. A directional coupling switch in MQW GaAs/AlGaAs material has allowed the enhanced electro-optic effect in the material to be utilised, without experiencing the large electro-absorption in the material associated with the QCSE. The device operates at low voltages (~4volts) and can give an on/off ratio of 30dB. Photocurrent spectroscopy on samples have shown a shift of the el-hhl and el-lhl exciton transitions which is quadratic with electric field strength and demonstrated the dominance of forbidden transitions in the absorption spectrum at large electric field strengths.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Electrical engineering, Condensed matter physics
• Date of Award: 1990
• Depositing User: Enlighten Team
• Unique ID: glathesis:1990-78203
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:37
• Last Modified: 30 Jan 2020 15:37
• URI: https://theses.gla.ac.uk/id/eprint/78203