Defects micropipes

Similar research has been done on planes perpendicnlar to the [0001] basal plane. Micropipe-free material has been grown, however, new defects appear as reported by the authors [60]. 

The sublimation sandwich method (SSM) is similar to the sublimation method, except for the small distance between source powder and substrate, 2-5 mm [10-12], Ga or GaN was used as a source and the substrate was sapphire or 6H-SiC. The optimal growth temperature was around 1200°C as temperatures lower than 1150°C caused the formation of structural defects such as voids and micropipes. Polycrystalline GaN was grown under 1050°C. At higher temperatures, GaN was thermally decomposed. The growth rate is much higher, up to 300 pm/hr [10] or 0.2 - 1.1 mm/hr [12], and crystalline GaN with the maximum thickness of 500 pm could be obtained. 

In order to produce SiC material of the level of quality required for device applications, chemical vapor deposition (CVD) is currently used as the primary growth technique for SiC epitaxy [2], Due to the continuous improvements in commercial substrate quality, the presence of micropipes in SiC epilayers is not the device yield limiting issue as it was a decade ago. However, the epitaxially grown SiC films still suffer from other extended defects such as basal plane and threading edge dislocations as well as point defects. The vision of growing SiC on porous SiC was to reduce the concentration of these defects and thus improve the epitaxial layer quality for device applications. 

SiC power devices are expected to be superior to Si devices even at room temperature. However, the practical difficulties are related to a limited yield of large area devices due to the existence of so-called micropipes (or voids) [10]. The density of these micron size defects has steadily decreased over the years reaching approximately 100 to 400 cm 2 in the state-of-the-art 6H-SiC substrates [11]. These defects are formed during the substrate growth. They... 

Recent reviews on the growth of high-purity SiC single crystals and their properties have been given by Muller et al. [195] and Augustine et al. [196]. Today, wafer diameters up to 50 mm are feasible on an industrial scale for the polytypes 4H and 6H the density of micropipe defects can be reduced to less than 100 cm (down to about 1 cm ). 

Fig. 13.12 Epitaxial growth on SiC. Reflection images. (a) SiC substrate, showing superdislocations and micropipe defects, (b) GaN epilayer, showing the strains that have been transmitted through to the layer. ...

The possibility of device fabrication based on SiC depends on defects such as micropipes in crystals and layers. Hence the investigation and control of the problem of micropipes are of extreme significance. The first step of our laboratory in this direction is to study the micropipe behavior in 6H-SiC single crystalls under high-temperature annealing (19). 

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