Growth and thermal properties of doped monocrystalline titanium-silicide based quantum dot superlattices

International audienceThis paper presents the growth mechanism of a monocrystalline silicide quantum dot superlattices (QDSL) grown by reduced pressure chemical vapor deposition (RPCVD). QDSL are made of TiSi2-based nanodots scattered in a p-doped Si90Ge10 matrix. It is the first time that the growth of a p-type monocrystalline QDSL is presented. We focus here on the growth mechanisms of QDSL and the influence of nanostructuration on their thermal properties. Thus, the dots surface deposition, the dots embedding mechanisms and the final QDSL growths are studied. The crystallographic structures and chemical properties are presented, as well as the thermal properties. It will be shown that some specific mechanisms occur such as the formation of self-formed quantum well superlattices and the dopant accumulation near the quantum dots. Finally, a slight decrease of the QDSL thermal conductivity has been measured compared to the reference sample

The visualization of Silicon nanoparticles by 3D electron tomography: use of mass-thickness contrast bright field imaging

International audienc

Minority carrier lifetime measurement in nanowire-based solar cells by a reverse recovery transient method

session Nanostructures (Y11.4)International audienc

The visualization of Silicon nanoparticles by 3D electron tomography: use of mass-thickness contrast bright field imaging

International audienc

The visualization of Silicon nanoparticles by 3D electron tomography: use of mass-thickness contrast bright field imaging

International audienc

Silicon nanocrystals grown on amorphous silicon carbide alloy thin films for third generation photovoltaics

International audienc

Energy harvesting from nanostructures

session oral presentation D1-1 (invited)International audienceWe present nanostructure based piezoelectric and thermoelectric energy harvesters. Using different forms of nanostructuration (heterostrucutration, composite materials, superlattices) further helps improving the performance of such nanodevices that could be used both as self-powered sensors and nanogenerators with IC compatibility. GaN and ZnO nanowires are used as piezoelectric devices. While a specific AFM method is used to investigate the individual nanowire properties, large area prototypes composed of nanowire arrays are realized to evaluate the performance of such nanogenerators. Bottom-up techniques using industrial tools are also used to grow Si/SiGe quantum dot superlattices, both n and p types, mono- or poly-crystalline to be used as thermoelectric elements where nanostructuration improves the ZT figure of merit. Going even further, for the first time we report the realization of Ti and Mo silicide quantum dot superlattices, both n an p type

Aluminum catalyzed growth of silicon nanowires: Al atom location and the influence of silicon precursor pressure on the morphology

We study the growth of silicon nanowires (SiNWs) by chemical vapor deposition (CVD) with aluminum as catalyst. We show that for a growth temperature of 600 °C, the silicon precursor partial pressure (SiH 4 in this study) is a key parameter for controlling the structural quality of the resulting SiNWs. We find by transmission electron microscopy that at high SiH 4 partial pressure, the SiNWs are composed of a monocrystalline core with a high density of surface defects, mainly twins, sheathed by a rough amorphous silicon layer. By contrast, at low SiH 4 partial pressure, the SiNWs are monocrystalline with a lower density of surface crystalline defects and a smooth surface. For the low SiH 4 partial pressure SiNWs, Al atoms have been detected at the SiNW surface by Auger spectroscopy at level around 3 at% and in the SiNW core by energy dispersive X-ray spectroscopy (EDS) at levels around 1 at%. Interestingly, higher Al concentrations are measured inside the nano-twin domains by EDS (around ten times increase). Two possible explanations are proposed; stacking faults are induced by Al atoms that lower their energy formation, or Al atoms can be trapped inside these stacking faults due to segregation effect during growth. These findings will be important for growing high quality SiNWs using Al as metal catalyst in reduced-pressure CVD tool. © 2012 Elsevier B.V

Molybdenum-based bilayer back contacts for CIGS solar cells on metatlic substrates

International audienc

Al catalyzed growth of silicon nanowires and subsequent in situ dry etching of the catalyst for photovoltaic application

Aluminum-catalyzed epitaxial growth of silicon nanowire (SiNW) arrays was performed on Si wafer by chemical vapor deposition at 600°C. The arrays showed a low optical total reflectance in the visible light spectrum, with a minimum of 2% around 450nm wavelength. Following SiNW growth, dry etching of the Al catalyst was performed in situ using HCl chemistry at 600°C. The effectiveness of aluminum etching was assessed by energy dispersive X-ray spectroscopy, by high resolution transmission electron microscopy and by a controlled growth experiment. This SiNW array growth and subsequent catalyst dry etching opens up the possibility of an all in vacuum fabrication process of radial junction solar cells. Al catalyst dry etching following growth using HCl gas at 600°C. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim