  Nanocrystalline Si and Ge are of high interest for integrated Si photonics
related to light emission, optical sensors, photodetectors, solar energy
harvesting and conversion devices, and also for floating gate non-volatile
memories (NVMs). In this review, we have focused on nanocrystalline porous Si
(nc-PS) with extension to Si nanodots, and Ge nanocrystals (NCs)/quantum dots
(QDs)/nanoparticles (NPs) embedded in oxides (SiO$_2$, TiO$_2$, HfO$_2$,
Al$_2$O$_3$). The great asset of nc-PS is its intense photoluminescence in VIS
at room temperature (RT), while Ge NCs/NPs embedded in oxides show high
photosensitivity in VIS-NIR-SWIR in the spectral photocurrent up to 1325 nm at
RT. Ge NCs/NPs/QDs floating gate NVMs present high memory performance, the
retention characteristics corresponding to the state of the art for NCs
floating gate NVMs. We prove the relevance of controlling the preparation
parameters for obtaining films with targeted photoluminescence,
photosensitivity and charge storage properties for applications, e.g.
VIS-NIR-SWIR optical sensors and photodetectors, and electronic and
photoelectric NVMs. We evidence the correlation of preparation conditions,
morphology, composition and crystalline structure with optical, electrical,
photoelectrical and charge storage properties and also evidence the
contribution of quantum confinement effect, localized states and trapping
centers.
