Time resolved investigations of field screening in InGaAs/InGaAIAs and InGaAs/InGaAsP multiple quantum wrll devices

Integrated high-speed intensity modulators based on the quantum confined stark effect (QCSE) are highly attractive devices for optical communication systems. We investigated two different important well/barrier material combinations suitable for long-wavelength modulators, namely, InGaAs/InGaAsP and InGaAs/InGaAlAs. We show that the difference in the band discontinuities between the two material systems has a large influence on modulator performance. We used a combined theoretical and experimental approach to evaluate this difference. A carrier transport model was developed which includes tunneling between wells, transfer to confinement layers, recombination and thermionic emission. With this model the carrier population of the wells and the internal field within the device after optical carrier injection was calculated. The absolute change of the internal field after pulsed excitation and the speed of recovery back to the external field shows the sensitivity of the modulator to incoming light. The structures studied consisted of five l0nm InGaAs quantum wells separated by 5nm barriers of either InGaAsP or InGaAlAs with 100 nm of linear confinement layers each side of the quantum well regions. The bandgap of the barrier and confinement layers was 1.3μm . The structures were grown on n-doped substrates and had p-doped contact layers. We conclude that InGaAs/InGaAsP quantum wells are more suitable for QCSE modulator than are InGaAs/InGaAlAs devices.