Papers by Author: Adolf Schöner

Abstract: In this work we report on the growth and preparation of 3C-SiC(111) material for metal-oxide-semiconductor (MOS) application. In order to achieve reasonable material quality to prepare MOS capacitors several and crucial steps are needed: 1) heteroepitaxial growth of high quality 3C-SiC(111) layer by vapour-liquid-solid mechanism on 6H-SiC(0001) substrate, 2) surface polishing, 3) homoepitaxial re-growth by chemical vapour deposition and 4) use of an advanced oxidation process combining plasma enhanced chemical vapour deposition (PECVD) SiO2 and short post-oxidation steps in wet oxygen. Combining all these processes the interface traps density (Dit)can be drastically decreased down to 1.2  1010 eV-1cm-2 at 0.63 eV below the conduction band. To our knowledge, these values are the best ever reported for SiC material in general and 3C-SiC in particular.

Abstract: p-type 3C-SiC samples were implanted by iron (Fe) and investigated by means of deep level transient spectroscopy (DLTS). Corresponding argon (Ar) profiles with similar implantation damage were implanted in order to distinguish between iron-related defects and defects caused by implantation damage. Two donor-like iron-related centers were identified in p-type 3C-SiC.

Abstract: This paper describes a novel design to achieve sensitive and stable performance of an avalanche photodiode based on silicon carbide material. The design includes a field-stopping layer with limited extension, and junction termination, in order to achieve avalanche multiplication only in the central region of the device. Also, sensitivity is increased by the achievement of a rectangular field distribution, and full depletion of the absorption region by the onset of avalanche multiplication. Evaluation of devices produced with this design show that a low leakage current and a sharp and stable avalanche breakdown point around 120V is achieved. Optical responsivity to radiation of wavelength 200 to 400 nm is shown to increase with increasing applied reverse bias, until a factor of 8 increase is achieved at the breakdown voltage.

Abstract: The electrical properties of oxides fabricated on n-type 3C-SiC (001) using wet oxidation and an advanced oxidation process combining SiO2 deposition with rapid post oxidation steps have been compared. Two alternative SiO2 deposition techniques have been studied: the plasma enhanced chemical vapor deposition (PECVD) and the low pressure chemical vapor deposition (LPCVD). The post-oxidized PECVD oxide is been demonstrated to be beneficial in terms of interface traps density and reliability.

Abstract: In this work, the electrical performance in terms of maximum current gain, ON-resistance and blocking capability has been compared for 4H-SiC BJTs passivated with different surface passivation layers. Variation in BJT performance has been correlated to densities of interface traps and fixed oxide charge, as evaluated through MOS capacitors. Six different methods were used to fabricate SiO2 surface passivation on BJT samples from the same wafer. The highest current gain was obtained for PECVD deposited SiO2 which was annealed in N2O ambient at 1100 °C during 3 hours. Variations in breakdown voltage for different surface passivations were also found, and this is attributed to differences in fixed oxide charge that can affect the optimum dose of the high voltage JTE termination.

Abstract: Intrinsic defects in 3C-SiC are generated by implantation of H+- and He+-ions or irra¬diation with high energy electrons. The defect parameters and the thermal stability of the observed defects are determined. The capture-cross-section of the W6-center is directly measured by variation of the filling pulse length. The charge state of the W6-center is obtained from double-correlated DLTS investigations according to the Poole-Frenkel effect.

Abstract: 3C-SiC/SiO2-capacitors are fabricated by over-oxidation of an implanted Gaussian nitrogen (N) profile and investigated by conductance spectroscopy. A double peak structure is observed in the conductance spectra indicating two types of traps, which change their charge state at identical time constant, however, which are located at different energy positions in the bandgap of 3C-SiC. The experimental G/w-V and C-V characteristics are simulated and the existence of two types of traps is verified in the framework of a theoretical model.

Abstract: The boron diffusion in three kinds of group IV semiconductors: silicon, silicon carbide and synthetic diamond has been studied by secondary ion mass spectrometry. Ion implantation of 300 keV, 11B-ions to a dose of 21014 cm-2 has been performed. The samples are subsequently annealed at temperatures ranging from 800 to 1650 °C for 5 minutes up to 8 hours. In silicon and silicon carbide, the boron diffusion is attributed to a transient process and the level of out-diffusion is correlated to intrinsic carrier concentration. No transient, out-diffused, boron tail is revealed in diamond at these temperatures.

Abstract: The in-situ doping of aluminum and nitrogen in migration enhanced embedded epitaxy (ME3) is investigated with the aim to apply it to the realization and fabrication of all-epitaxial, normally-off 4H-SiC JFET devices. This ME3 process consists of the epitaxial growth of an n-doped channel and a highly p-doped top gate in narrow trenches. We found that the nitrogen doping in the n-channel (a-face) is a factor 1.5 higher than layers grown with the same process on Si-face wafers. Due to the low C/Si ratio and the low silane flow rate used in the ME3 process, the growth of the p-doped top gate needs high flow rates of the aluminum precursor trimethylaluminum for several hours, which contaminates the CVD reactor and causes aluminum memory effects. These aluminum memory effects can be reduced by an extra high temperature bake-out run.

Abstract: The migration enhanced embedded epitaxy (ME3) mechanism and 2D dopant distribution of the embedded trench region is investigated with the aim to realize the all-epitaxial, normally-off junction field effect transistor (JFET). We found that the embedded growth consists of two main components. First one is the direct supply without gas scattering and the other one is the surface migration supply via the trench opening edge, which dominate the ME3 process. An inhomogeneous 2D distribution of Aluminum (Al) concentration was revealed for the first time in the 4H-SiC embedded trench regions by the combined analysis of secondary ion mass spectrometry (SIMS) and scanning spreading resistance microscopy (SSRM) results. The maximum variation of Al concentration in the trench is estimated to be about 4-times, which suggests that the Al concentration is highest for the (0001) plane and lowest for the trench corner (1-10x) plane. Al concentration in the (1-100) plane, which determines the JFET p-gate doping level is 1.5-times lower than (0001) plane for trench region fabricated on Si-face wafers.