Jesse Groenen

Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application.

Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (≤5 keV) ion implantation method followed by conventional thermal annealing at 800°C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 × 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of ± 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices.

Controlled fabrication of Si nanocrystal delta-layers in thin SiO2 layers by plasma immersion ion implantation for nonvolatile memories

Plasma Immersion Ion Implantation (PIII) is a promising alternative to beam line implantation to produce a single layer of nanocrystals (NCs) in the gate insulator of metal-oxide semiconductor devices. We report herein the fabrication of two-dimensional Si-NCs arrays in thin SiO2 films using PIII and rapid thermal annealing. The effect of plasma and implantation conditions on the structural properties of the NC layers is examined by transmission electron microscopy. A fine tuning of the NCs characteristics is possible by optimizing the oxide thickness, implantation energy, and dose. Electrical characterization revealed that the PIII-produced-Si NC structures are appealing for nonvolatile memories.

Acoustics at nanoscale: Raman–Brillouin scattering from thin silicon-on-insulator layers

We report on Raman–Brillouin scattering from thin single silicon layers. Starting from a 33 nm silicon-on-insulator structure, a series of layers with progressively decreasing thicknesses was prepared using a chemical treatment consisting of oxide stripping/formation cycles. In order to determine these thicknesses, experimental Raman–Brillouin spectra are compared to calculations performed in the frame of the photoelastic model. We demonstrate that subnanometer changes in the silicon layer thickness can be derived from a proper analysis of the spectral response. It is shown that a 1 nm thick oxide forms during the chemical treatment.

Studying Thin Ge Films and Ge/GeO 2 Interfaces by Means of Raman-Brillouin Scattering

The high frequency acoustic phonons employed in Raman–Brillouin scattering are used to probe native oxide layers on Ge film surfaces in GeO2/Ge/InxGa1–xAs heterostructures. The thermal instability of GeO2 results in the production of GeO gas on Ge surfaces; molecules of this gas evaporate through the porous GeO2 layers. As a result, the Ge/GeO2 interface is depleted of Ge, and a sub-stoichiometric GeOx layer is formed. By comparing photoelastic modeling and experimental results, we discovered a 0.5 nm thick interfacial region between the film and the oxide, demonstrating the sensitivity of acoustic phonons to the subnanometer scale.

Raman-Brillouin scattering from a thin Ge layer: Acoustic phonons for probing Ge/GeO2 interfaces

We report on Raman–Brillouin scattering by acoustic phonons from a thin Ge layer. The high frequency acoustic phonons involved in this scattering are used to probe the native oxide present on top of the Ge layer. By comparing experiment and photoelastic modelling, a quantitative analysis is performed which shows that an interfacial layer is located in between the Ge and GeO2 oxide layers. The native oxide is found to be composed of a 0.5 nm thick interfacial layer and a 1 nm thick GeO2 layer on top of it. Sensitivity down to the sub-nm scale is evidenced.

Scattering of light by sound on a nanoscale

We report on light scattering experiments (Raman-Brillouin) in semiconductor quantum wells and quantum dots nanostructures. All measurements were performed under resonant excitation of the optical transitions involving confined electronic states. The scattered light was detected in the very low-frequency range around the Rayleigh line. We observe strong oscillations of the scattered intensity. Their period and relative amplitudes depend on the sample characteristics (size, density and spatial distribution of nano-objects). We show that such signal originates from interference effects due to the interaction between sound waves and the excited electronic density. By comparing simulated and measured spectra, we are able to extract, from the experiments, sample characteristics such as average size and size distribution of quantum dots. This optical sensing technique, namely Raman interferometry, is similar to the well-known X-ray diffraction technique, in the sense that it allows imaging of electronic states in the reciprocal space. Moreover, we show that Raman interferometry is a surface sensitive technique. By using quantum dots and quantum wells as Thz acoustic-detectors we are able to measure the reflection of sound waves at the sample surface. The surface characteristics (nano-scale roughness and oxidation) can be addressed using this method.