Modelling of electroabsorption in coupled quantum wells with applications to low voltage optical modulation

The authors model the room temperature electroabsorption of coupled double quantum wells using a transfer matrix technique to calculate carrier wavefunctions and their overlaps. Their behaviour with an electric field is compared with uncoupled multiple quantum wells with optical modulation in mind. Consideration of wavefunctions and energy levels allows them to choose a coupled well structure with good optical modulation at a low electric field. By fitting three parameters once, they predict absorption spectra. These are used to assess coupled quantum wells within an asymmetric Fabry-Perot reflection modulator. Very low voltage operating characteristics were calculated allowing for a total fluctuation in the coupling barrier width of one monolayer: a contrast ratio of 2.1:1, an insertion loss of 3.3 dB and an applied voltage of only 0.7 V; alternatively, a very high contrast with an insertion loss of 9.4 dB operating at 2.2 V. However, these predictions may be difficult to fulfil in devices grown at present because of the built-in field within the intrinsic region of a p-i-n diode.