Aluminum doping of 4H-SiC by irradiation of excimer laser in aluminum chloride solution

We have found that aluminum doping into 4H-SiC is performed by irradiating excimer laser light to 4H-SiC immersed in aluminum chloride solution. Aluminum is introduced in SiC at the concentration of over 1 × 1020 cm−3 near the surface while, chlorine hardly diffuses into 4H-SiC. After the laser irradiation in aluminum chloride solution, the resistance of the laser-irradiated region decreases with increasing laser fluence. Hall effect measurement shows that the laser irradiation produces a p-type layer and that its sheet carrier concentration is 2.14 × 1011 cm−2. In addition, we produce a pn junction by doping the surface of n-type 4H-SiC and by aluminum doping. The pn junction shows rectifying characteristics whose on/off ratio is about 7 decades and ideality factor is 1.15. This technique is one of the strong candidate local doping techniques for SiC.

Source:IOPscience
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Effects of sacrificial oxidation on surface properties of n- and p-type 4H-SiC: implications for metal contact behaviors

A comparative investigation on the effects of sacrificial oxidation (SO) on the surface properties of n- and p-type 4H-SiC has been conducted by using x-ray photoelectron spectroscopy and deep level transient spectroscopy. For n-type 4H-SiC, the surface Fermi level is unpinned and shifts towards conduction band edge due to significant reduction of surface contaminants and removal of surface defects by SO. For p-type 4H-SiC, the surface contamination is also reduced with a shift of Fermi level towards valance band edge after SO. However, a high density of carbon interstitials related defects is likely to be generated close to the valance band during the oxidation. Pronounced Fermi level pinning may be still present with surface states density higher than 1.65 × 1012 cm−2 eV−1. The implications of SO on the electrical behaviors of metal contacts to n- and p-type 4H-SiC have been proposed.

Source:IOPscience
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Scanning tunnelling microscopy imaging and spectroscopy of p-type degenerate 4H-SiC(0001)

In this work we present scanning tunnelling microscopy (STM) imaging and spectroscopy of a highly p-doped wide bandgap semiconducting 4H-SiC(0001) surface. Whereas n- and p-doped 6H-SiC or n-doped 4H-SiC surfaces can be relatively easily imaged with the STM, the p-doped 4H-SiC cannot be imaged due to the absence of any surface conductivity. This is very surprising given the presence of a p-doped, degenerate epitaxial layer. The behaviour can be explained by the formation of a Schottky barrier either between the tip and the surface or between the surface and the sample holder, depending on the polarity of the applied voltage. We found that prolonged and repeated exposures of the SiC surface to a Si atomic flux followed by thermal annealing are required before the surface conductivity is sufficient to allow STM images to be recorded. The result is the deposition of overlayers of Si, with structures similar to Si(111) 7 × 7, Si(113) 3 × 2, and Si(110) 16 × 2 rather than the expected stable SiC(0001) 3 × 3 reconstruction. We have further demonstrated the ability of scanning tunnelling spectroscopy to distinguish between the Si and the SiC phases based on the difference in their bandgaps.

Source:IOPscience
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