Influence of Triangle Structure Defect on the Carrier Lifetime of the 4H-SiC Ultra-Thick Epilayer

Effect of triangle structure defects in a 180-μm-thick as-grown n-type 4H-SiC homoepitaxial layer on the carrier lifetime is quantitatively analyzed, which is grown by a horizontal hot-wall chemical vapor deposition reactor. By microwave photoconductivity decay lifetime measurements and photoluminescence measurements, the results show that the average carrier lifetime of as-grown epilayer across the whole wafer is 2.59 μs, while it is no more than 1.34 μs near a triangle defect (TD). The scanning transmission electron microscope results show that the triangle structure defects have originated from 3C-SiC polytype and various types of as-grown stacking faults. Compared with the as-grown stacking faults, the 3C-SiC polytype has a great impact on the lifetime. The reduction of TD is essential to increasing the carrier lifetime of the as-grown thick epilayer.

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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A comparative study of the structure and energetics of elementary defects in 3C- and 4H-SiC

The potential non-equivalent defects in both 3C- and 4H-SiC are classified by a new method that is based on symmetry considerations. In 4H-SiC their number is considerably higher than in 3C-SiC, since the hexagonal symmetry leads to diversification. The different theoretical methods hitherto used to investigate defects in 3C-SiC are critically reviewed. Classical MD simulations with a recently developed interatomic potential are employed to investigate the stability, structure and energetics of the large number of non-equivalent defects that may exist in 4H-SiC. Most of the potential defect configurations in 4H-SiC are found to be stable. The interstitials between hexagonal and trigonal rings, which do not exist in 3C-SiC, are characteristic for 4H-SiC and other hexagonal polytypes. The structure and energetics of some complex and anisotropic dumbbells depend strongly on the polytype. On the other hand, polytypism does not have a significant influence on the properties of the more compact and isotropic defects, such as vacancies, antisites, hexagonal interstitials, and many dumbbells. The results allow conclusions to be drawn about the energy hierarchy of the defects.

Source:IOPscience

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Scanning tunnelling microscopy imaging and spectroscopy of p-type degenerate 4H-SiC

In this work we present scanning tunnelling microscopy (STM) imaging and spectroscopy of a highly p-doped wide bandgap semiconducting 4H-SiC 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 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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