Papers by Author: Giuseppe Abbondanza

Abstract: In this paper we study the surface morphology of <11-20> 4° degree off, silicon terminated, 4H Silicon Carbide (4H-SiC) in terms of growth parameters and post growth argon thermal annealing. We find that out-of-equilibrium conditions favor the reduction of the surface roughness. Furthermore, we find preliminary indications that the same growth parameters that lead to the reduction of the surface roughness promote also a reduction of (1,3) and (4,4) stacking faults density.

Abstract: Raman microscopy has been used to study transport properties in hetero-epitaxial 3C-SiC/Si thin films. By an accurate analysis of the Longitudinal Optic phonon-plasmon coupled (LOPC) modes in n-type doped 3C-SiC films, free carrier density and mobility has been determined. A study of doped 3C-SiC reveals a strong relationship between the calculated free carrier density and both the C/Si ratio used during the epitaxial process and Silicon substrates orientation on which 3C-SiC thin films were grown (maintaining the N2 gas flow rate). The free carrier density obtained is in the range between 5x1016 cm-3 and 4x1018 cm-3. Epitaxial films grown on (111) Si substrates show a higher free carrier density and a lower dependence on C/Si ratios as compared to films grown on (100) Si substrates.

Abstract: Growth of 3C-SiC films on an off-axis (111) Si substrate, with a miscut of 4° towards the <110> direction, is here reported. An extensive material characterization has been conducted by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Raman spectroscopy, indicating a very promising film quality with extremely flat surface and interface. Notwithstanding the excellent film quality, the wafer bow is still limiting its full employment in device realization.

Abstract: 3C-SiC devices are hampered by the defect density in heteroepitaxial films. Acting on the substrate, it is possible to achieve a better compliance between Si and 3C-SiC. We present here an approach to favorite defect geometrical reduction in both [ ] and [ ] directions by creating Inverted Silicon Pyramids (ISP). A study of 3C-SiC growth on ISP is reported showing benefits in the film quality and a reduction in the linear density of stacking faults. Growth on ISP leads also to a decrease in the 3C-SiC residual stress as well as in the bow of the Si/SiC system.

Abstract: Gallium nitride (GaN) and related alloys (AlxGa1-xN) are promising semiconductors for high-frequency and high-power devices applications. In particular, the growth of AlGaN/GaN heterostructures on SiC substrates, due to the high thermal conductivity of SiC, can lead to significant improvement in the device performances. An important issue in the fabrication of AlGaN/GaN devices is the influence of the required thermal budget (700-900°C) on the properties of Ohmic contacts and device isolation. In this work, the influence of thermal annealing on the fabrication of AlGaN/GaN devices was studied. Ti/Al/Ni/Au multilayers led to an Ohmic behavior with a specific resistance c in the 10-5 cm2 range upon annealing between 750°C and 850°C. The electrical behavior of Ohmic contacts was correlated with the evolution of the formed phases and with the temperature behavior of c. The stability of the inter-device isolation obtained by nitrogen-implantation during annealing at these temperatures was also monitored.

Abstract: The design and the experimental results of some prototypes of SiC X-ray detectors are presented. The devices have been manufactured on a 2’’ 4H-SiC wafer with 115 m thick undoped high purity epitaxial layer, which constitutes the detection’s active volume. Pad and pixel detectors based on Ni-Schottky junctions have been tested. The residual doping of the epi-layer was found to be extremely low, 3.7 x 1013 cm-3, allowing to achieve the highest detection efficiency and the lower specific capacitance of the detectors. At +22°C and in operating bias condition, the reverse current densities of the detector’s Schottky junctions have been measured to be between J=0.3 pA/cm2 and J=4 pA/cm2; these values are more than two orders of magnitude lower than those of state of the art silicon detectors. With such low leakage currents, the equivalent electronic noise of SiC pixel detectors is as low as 0.5 electrons r.m.s at room temperature, which represents a new state of the art in the scenario of semiconductor radiation detectors.

Abstract: The choice of off-axis (111) Si substrates is poorly reported in literature despite of the ability of such an oriented Si substrate in the reduction of stacking faults generation and propagation. The introduction of off-axis surface would be relevant for the suppression of incoherent boundaries. We grew 3C-SiC films on (111) Si substrates with a miscut angle from 3° to 6° along <110> and <11 >. The film quality was proved to be high by X-Ray diffraction (XRD) characterization. Transmission electron microscopy was performed to give an evaluation of the stacking fault density while pole figures were conducted to detect microtwins. Good quality single crystal 3C-SiC films were finally grown on 6 inch off-axis (111)Si substrate. The generated stress on both 2 and 6 inch 3C-SiC wafers has been analyzed and discussed.

Abstract: The growth rate of 4H-SiC epi layers has been increased up to 100 µm/h by chlorine addition. The epitaxial layers grown with this process have been characterized by electrical, optical and structural characterization methods. Very thick (> 100 µm) epitaxial layer has been grown and the Schottky diodes realized on these layers have good yield (> 87%) with a low defect density (10/cm2). This process gives the opportunity to realize very high power devices with breakdown voltages in the range of 10 kV or X-Ray and particle detectors with a low cost epitaxy process.

Abstract: A process has been developed to grow multi-epy high doped structure. Trichlorosilane (TCS) and Ethylene have been used as precursor; Nitrogen (N2) and trimethylaluminum (TMA) as doping source. The SIMS and SCM analysis show that using this silicon precursor very abrupt N++/P+/N+ junctions (40-60 nm) can be obtained with low background doping concentration in a single epitaxial growth run.

Abstract: The growth rate of 4H-SiC epi layers has been increased up to 100 µm/h with the use of trichlorosilane instead of silane as silicon precursor. The epitaxial layers grown with this process have been characterized by electrical, optical and structural characterization methods. Schottky diodes, manufactured on the epitaxial layer grown with trichlorosilane at 1600 °C, have higher yield and lower defect density in comparison to diodes realized on epilayers grown with the standard epitaxial process.