Grazia Litrico

High Quality Single Crystal 3C-SiC(111) Films Grown on Si(111)

We have developed a high-quality growth process for 3C-SiC on on-axis (111)Si substrates with the ultimate goal to demonstrate high quality and yield electronic and MEMS devices. A single-side polished 50 mm (111)Si wafer was loaded into a hot-wall SiC CVD reactor for growth. The 3C-SiC process was performed in two stages: carbonization in propane and hydrogen at 1135°C and 400 Torr followed by growth at 1380°C and 100 Torr. X-ray diffraction rocking curve analysis of the 3C-SiC(222) peak indicates a FWHM value of 219 arcsec. This is a very interesting result given that the film thickness was only 2 µm, thus indicating that the grown film is of very high quality compared with published literature values. X-ray polar figure mapping was performed and it was observed that the micro twin content was below the detection limit. Therefore TEM characterization was performed in plan view to allow assessment of the stacking fault density as well as confirmation of the very low micro twin concentration in this film. TEM analysis indicates a low concentration of stacking faults in the range of 104 cm-1.

Optical and electrical properties of 4H-SiC epitaxial layer grown with HCl addition

The introduction of hydrogen chloride (HCl) in the deposition chamber during the growth of 4H-SiC epitaxial layers allows very high growth rates to be achieved. The properties of the epilayers and the growth rate depend on many parameters such as the growth temperature and the C/Si, Cl/Si, and Si∕H2 ratios. We have used optical and electrical measurements to investigate the effect of the Cl/Si and Si∕H2 ratio and growth temperature on the epitaxial growth process. The growth rate increases with increasing Si∕H2 ratio and higher growth rates are obtained when HCl is added to the gas flow. Optical microscopy shows an improvement of the surface morphology, and luminescence measurements reveal a decrease in the concentration of complex defects with increasing Cl/Si ratio in the range of 0.05–2.0 and with increasing growth temperature from 1550 °C to 1650 °C. The electrical measurements on the diodes realized on these epitaxial layers show a decrease of the leakage current with increasing Cl/Si ratio and growt...

Electrical properties of high energy ion irradiated 4H-SiC Schottky diodes

The changes in the electrical properties of 4H-SiC epitaxial layer induced by irradiation with 7.0 MeV C+ ions were investigated by current-voltage measurements and deep level transient spectroscopy (DLTS). Current-voltage characteristics of the diodes fabricated from epilayers doped with different nitrogen concentrations were monitored before and after irradiation in the fluence range of 109–1010 cm−2. The leakage current was not changed after irradiation, while the forward current-voltage characteristics of the diodes showed an increase in the series resistance, which is mainly related to the high degree of compensation occurring near the end of the ion implant depth.The temperature dependence of the carrier mobility determined from the I-V measurements in the temperature range of 100–700 K shows a T−3 dependence of mobility as determined from the nonirradiated as well as the irradiated diodes. DLTS measurements of the irradiated diodes reveal the presence of two deep levels located at 0.98 and 1.4 eV b...

Controlled large-scale fabrication of sea sponge-like ZnO nanoarchitectures on textured silicon

A simple and effective approach to fabricate extensive 3D ZnO nanoarchitectures on alkaline etched (100) Si substrates is presented. Textured silicon micropattern drives ZnO 1D growth on all the {111} exposed faces, resulting in sea sponge-likeZnO nanoarchitectures. The obtained 3D nanostructured ZnO is the result of a perfectly ordered array of continuous and crystalline ZnO nanorods, grown on the silicon pyramid {111} faces. The substrate orientation and the relative roughness, intrinsically derived by the alkaline silicon texturization, drive the preferential growth of one-dimensional ZnO nanorods. The ZnO nanorods photoluminescence spectra show, at room temperature, a narrow ultraviolet (UV) emission peak at 3.28 eV and a broad unstructured green band emission at 2.57 eV. These luminescence emissions are attributed to the near band-edge exciton transitions and to the defect emission, respectively. This original approach to fabricate high surface area ZnO nanoarchitectures presents the advantages of well established and reproducible methodologies of semiconductors industrial manufacturing (silicon micromachining and chemical vapor deposition), thus representing an easy scaling up solution to fabricate new ZnO-based nanomaterials.

Physical Vapor Growth of Double Position Boundary Free, Quasi-Bulk 3C-SiC on High Quality 3C-SiC on Si CVD Templates

We have developed and investigated the quasi-bulk crystal growth of 3C-SiC on transferred, high quality, CVD-grown templates using a sublimation sandwich related technique. The seeding layers were removed from the silicon carrier using a solution of hydrogen fluoride, nitric acid and water and glued to a substrate using carbon glue. The transferred layers were used as seeding material to grow high quality, single crystalline, DPBs free 3C-SiC crystals with thicknesses of up to 860 μm and a size of 18 x 20 mm. Analysis of the 3C-SiC layers was carried out using Laue measurement in back-reflecting geometry, Raman spectroscopy and optical microscopy.

Study of the Effects of Growth Rate, Miscut Direction and Postgrowth Argon Annealing on the Surface Morphology of Homoepitaxially Grown 4H Silicon Carbide Films

we study the surface morphology of homoepitaxially grown 4H silicon carbide in terms of growth rate, miscut direction of the substrate and post growth argon thermal annealings. All the results indicate that the final surface morphology is the result of a competition between energetic reorganization and kinetic randomness. Because in all observed conditions energetic reorganization favors surface ondulations (“step bunching”), out-of-equilibrium conditions are one of the keys to favor the reduction of the surface roughness to values below ~0.5 nm. We theoretically support these results using kinetics superlattice Monte Carlo simulations (KslMC)

Optimisation of Epitaxial Layer Growth with HCl Addition by Optical and Electrical Characterization

High growth rate of 4H-SiC epitaxial layers can be reached with the introduction of HCl in the deposition chamber. The effect of the Cl/Si ratio on this epitaxial growth process has been studied by optical and electrical measurements. Optical microscopy shows an improvement of the surface morphology and luminescence measurements reveal a decrease of epitaxial layer defects with increasing the Cl/Si ratio in the range 0.05–2.0. The leakage current measured on the diodes realized on these wafers is reduced of an order of magnitude and DLTS measurements show a decrease of the EH6,7 level concentration in the same range of Cl/Si ratio. The value Cl/Si=2.0 allows to grow epitaxial layers with the lowest defect concentration.

Electrical properties of extended defects in 4H-SiC investigated by photoinduced current measurements

We study the correlation between crystal quality and electrical transport in 4H-SiC by micro-photoluminescence and laser-beam-induced photocurrent measurements. A focused HeCd laser at 325 nm has been employed to simultaneously measure, with a spatial resolution of a few microns, both the photoluminescence and current–voltage characteristics of 4H-SiC Schottky diodes. We found that the laser-induced photocurrent acquired along a defect can give information on its spatial distribution in depth and that the local minority carrier lifetime and generation depend on the type of stacking fault, both decreasing for defects with deeper intragap levels.

4H-SiC Epitaxial Layer Grown on 150 mm Automatic Horizontal Hot Wall Reactor PE106

Preliminary results of 150mm SiC 4H 4°off have been obtained with the new 150mm automatic horizontal hot wall reactor PE1O6, using chlorinated chemistry (SiHCl3 + C2H4). A new injection system has been tested in two configurations and results will be shown in this paper. AFM surface roughness measurements and epi defect density have been reported.

Effects of the Growth Rate on the Quality of 4H Silicon Carbide Films for MOSFET Applications

In this paper we investigate the role of the growth rate (varied by changing the Si/H2 ratio and using TCS to avoid Si droplet formation) on the surface roughness (Rq), the density of single Shockley stacking faults (SSSF) and 3C-inclusions (i.e. epi-stacking faults, ESF). We find that optimized processes with higher growth rates allow to improve the films in all the considered aspects. This result, together with the reduced cost of growth processes, indicates that high growth rates should always be used to improve the overall quality of 4H-SiC homoepitaxial growths. Furthermore we analyze the connection between surface morphology and density of traps (Dit) at the SiO2/SiC interface in fabricated MOS devices finding consistent indications that higher surface roughness (step-bunched surfaces) can improve the quality of the interface by reducing the Dit value.