Contactless modulated reflectivity spectroscopy, in forms of photoreflectance (PR) and contactless electroreflectance (CER), is presented as a useful tool for the investigation of semiconductor structures including nanometer-sized quasi 0D objects (like quantum dots or quantum dashes) obtained by self-assembly. There are discussed their advantages with respect to a certain kind of structures and including the problems of spurious background signals, below-band-gap oscillations and modulation mechanisms. Finally, recent results regarding the modulation spectroscopy on several types of novel 0D-like structures will be presented and it will concern the following: (i) modulation spectroscopy followed 2D-3D growth transition: wetting layer thickness determination and detection of the quantum dots formation in Stranski-Krastanow growth mode in different strain regimes for InGaAs/GaAs QDs; (ii) intermixing processes in self-assembled InAs/GaAs QD structures; (iii) excited states spectrum for new material/design quantum-dot-like structures (e.g. columnar InGaAs/GaAs QDs or InAs quantum dashes on InP substrate with different kind of quanternary barriers); (iv) electronic properties of semiconductor laser structures: different material quantum-dot-based lasers for fiber telecommunication range: InAs/GaAs dots for 1.3-1.55 mm; InAs/InP dashes for 1.55 mm and longer wavelengths; quantum dot (or dash) – quantum well tunnel injection systems based on GaAs or InP substrates; (v) modulation response intensity versus the nano-object size in different quantization regimes: for different size (volume) InAs/GaAs QDs or InAs/InP QDashes; (vi) modulation spectroscopy in high spatial resolution mode (microphotoreflectance on plane QD structures or single micrometer-sized pillar microresonators).

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1. Optical characterization of quantum dash based tunnel injection laser structures for 1.55 μm emission