Nanoscale probing of the lateral homogeneity of donors concentration in nitridated SiO2/4H–SiC interfaces

In this paper, nanoscale resolution scanning capacitance microscopy (SCM) and local capacitance–voltage measurements were used to probe the interfacial donor concentration in SiO2/4H–SiC systems annealed in N2O. Such nitrogen-based annealings are commonly employed to passivate SiO2/SiC interface traps, and result both in the incorporation of N-related donors in SiC and in the increase of the mobility in the inversion layer in 4H–SiC MOS-devices. From our SCM measurements, a spatially inhomogeneous donor distribution was observed in the SiO2/4H–SiC system subjected to N2O annealing. Hence, the effect of a phosphorus implantation before the oxide deposition and N2O annealing was also evaluated. In this case, besides an increased average donor concentration, an improvement of the lateral homogeneity of the active doping was also detected. The possible implications of such a pre-implantation doping of the near-interface region on 4H–SiC MOS-devices are discussed.

Source:IOPscience
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Efficient positron moderation with a commercial 4H-SiC epitaxial layer

We have studied the properties of a commercially available 4H-SiC epitaxial layer and evaluated its potential application as an efficient positron remoderator. A remoderation efficiency of more than 65% has been measured for incident positrons with 1 keV energy. We have determined the work function and the energy distribution of the emitted slow positrons, a property which is essential for practical applications. Comparison of the positron moderation properties of the epitaxial layer with results from a n-type 4H-SiC single crystal, indicate that the epitaxially grown layer is a superior secondary moderator than its substrate counterpart.

Source:IOPscience
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Improved ohmic contact to the n-type 4H-SiC semiconductor using cobalt silicides

Multilayer structures of cobalt and silicon have been deposited as an ohmic contact on n-type 4H-SiC substrates in order to obtain lower contact resistance and higher thermal stability. The metal structures were prepared by using electron beam evaporation on top of the silicon face of the 4H-SiC substrates, and were annealed in an atmosphere of argon with 10% hydrogen. The metal film thickness was monitored during the film deposition, and the ratio of the cobalt and silicon was fixed at 0.5 for the formation of the silicon-rich silicide structure (CoSi2). The electrical property of the ohmic contact has been significantly improved by the reduction of the oxide content in the metal contact layer. A two-step annealing process was employed to reduce oxidation problems that may occur in the heat treatment at high temperatures. The specific contact resistance of the contact structure prepared by the two-step annealing process was measured to decrease by more than one order of magnitude compared to that prepared by one-step annealing. The best result has been obtained as 1.8 × 10−6 Ω cm2 for Co/Si/Co/Si/Co metal structures after two-step annealing, at 500 °C for 600 s and 800 °C for 120 s. In the field emission scanning electron microscopy, the interface of the contact structure and SiC substrate was observed to have smooth surface morphology with CoSi2 grains.

Source:IOPscience
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Carrier transport properties in inversion layer of Si-face 4H–SiC MOSFET with nitrided oxide

We propose a method to evaluate the carrier transport properties in the inversion layer of 4H–SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) experimentally. Our approach differs from conventional methods, which have adjusted the parameters in conventional mobility models. Intrinsic phonon-limited mobility (μ phonon) in the SiC MOSFET was observed by suppressing the severe impact of Coulomb scattering on the SiC MOS inversion layer by lowering the acceptor concentration (N A) of the p-type well region to the order of 1014 cm−3. In this study, we investigated the carrier transport properties in the inversion layer of Si-face 4H–SiC MOSFETs with nitrided oxide. It is revealed that the μ phonon of the SiC MOSFET is a quarter or less than the conventionally presumed values. Additionally, surface roughness scattering is found not to be the most dominant mobility-limiting factor even at high effective normal field (E eff) for the SiC MOSFET. These results demonstrate that conventional understanding of carrier scattering in the SiC MOS inversion layer should be modified, especially in the high E eff region.

Source:IOPscience
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