Photo- and contactless electro-reflectance spectroscopies of step-like GaInNAs/Ga(In)NAs/GaAs quantum wells

Step-like GaInNAs/Ga(In)NAs/GaAs double quantum well (DQW) structures tailored at 1.3 μm have been studied in photoreflectance (PR) and contactless electroreflectance (CER) spectroscopies. Spectral features related to absorption in the active part of the step-like DQW structure, i.e. GaInNAs/Ga(In)NAs QW, as well as features related to absorption between states confined above the step-like barrier (SLB) and in GaAs barriers have been observed. It has been shown that these two techniques give information about the same optical transitions. However, due to some differences in the mechanism of band bending modulation, PR and CER spectra are not exactly the same especially for the layer which is under significant internal electric field. It has been shown that Franz-Keldysh oscillations related to GaAs cap layer are clearly observed in CER and disappear in PR at strong modulation conditions due to an effective flattering of the surface band bending during PR measurements.