Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization

Abstract

The development of new materials for shortwavelength infrared (SWIR) optical sensors is of high importance for the fast development of different applications, as, for example, Internet of Things, road safety, and pollution monitoring. Group IV SiGe provides more sustainable As-, Cd-, and Pb-free nanomaterials that are cheaper and ecologic and offer easy integration with CMOS technology. This Review is on Ge and SiGe quantum dots/nanocrystals (QDs/NCs) embedded in dielectrics for VIS-SWIR photodetection, in which we highlight and discuss photocurrent mechanisms, correlation of photodetection parameters and characteristics with crystalline structure, morphology and energy bandgap, and applications as photodetectors, optical sensors, phototransistors, and solar cells. The embedding matrix induces NC surface passivation, stress field, and nanocrystallization effects and brings specific advantages depending on the matrix material. SiGe NCs in oxides for VIS-SWIR sensing represents a niche domain, showing high photosensitivity (photocurrent) in SWIR up to 1.8 μm at room temperature and 2 μm at 100 K, deeper in SWIR than Ge. By alloying Ge with a small content of Si, NC thermal stability is much improved as the detrimental Ge fast diffusion in oxides is hindered and SWIR photosensing is enhanced due to light absorption in Ge-rich SiGe NCs.

Self-Diffusion of Ge in Amorphous GexSi1–x Films Studied In Situ by Neutron Reflectometry

“…Amorphous germanium–silicon (Ge–Si) solid solutions are an interesting class of materials from both a fundamental and technological point of view. Although Ge–Si is a long-known alloy, it is classified as an emerging material due to the renewed interest in a variety of applications, including solar cells, thermoelectrics, photonics, spintronics, quantum computing, − and as an active material , in negative electrodes of lithium-ion batteries (LIBs). − For the last case, silicon, germanium, and, hence Ge–Si solid solutions react with lithium via an alloying/dealloying process that stores and delivers on average ten times more of Li + charge per atom than graphite, the anode material in commercial LIBs. − …”

“…Planar Ge, Si, Ge/GeSi and Si/GeSi heterostructures with layer thicknesses between 15 and 500 nm are systems of choice not only for the fabrication and study of solar cells, but also for the study of carrier mobility in quantum technologies. − For the latter case confinement and quantum size effects (QSE) play a decisive role. − …”