Electro-optical investigations of strained InGaAs/GaAs double quantum well laser structures

Strained Al-free InGaAs/GaAs quantum well (QW) structures are now under intensive investigation due to the potential application in high power laser diodes. During their MOCVD growth the position of the pn junction is shifted towards the p-doped barriers due to the unintentional n-doping of the nominally intrinsic region. Although this shift deteriorates the electro-optical properties it is difficult to detect this effect. Systematic optical investigations performed on coupled double quantum well (CDQW) structures as a function of applied dc bias voltage demonstrate that a combination of photocurrent (PC) and electroreflectance (ER) measurements is not only capable of revealing this effect but also allows the determination of many details of the CDQW subband structure. A comparison of these experiments with calculated transition matrix elements makes a further optimization of both the layer structure and the growth process possible.