Limits to normal incidence electroabsorption modulation in GaAs/(GaAl)As multiple quantum well diodes

The achievable electroabsorption modulation in GaAs/(GaAl)As normal-incidence multiple-quantum-well (MQW) diodes with 50-Å and 100-Å well widths is assessed. It is suggested that modulation performance should be characterized by the transmission change (T _hi-T_lo) when the device is used in a simple source-modulator-detector communication link, whereas in more complex applications in which optical signals are merged, the contrast is more appropriate. For either transmission change or contrast there is an optimum number of wells which varies with design voltage, and this is used to calculate achievable modulation in the bias-absorbing mode for 100-Å and 50-Å well widths. The effects of improved smoothness at the interfaces and lower background dopings are investigated. It is found that a transmission change of 40% at 5 V is typical and does not improve significantly with better growth, while the achievable contrast depends strongly on the background doping. The results are compared with those of real modulators