Abstract
In this work, 4H-SiC epilayers are performed on 4° off-axis substrates under low pressure condition by horizontal hot wall chemical vapor deposition (HWCVD) with a standard chemistry of silane-propane-hydrogen, which focuses on the effects of growth pressure on morphology, basal plane dislocations (BPDs) and crystalline quality. It is found that morphological defects reduce with the decreasing of growth pressure, since the surface diffusion length of absorbed adatoms increases under low growth pressure, which suppresses the nucleation of adatoms on terraces and the formation of morphological defects. However, as the surface diffusion length increases under low growth pressure, the difference of growth velocity at steps is enhanced, which leads to the extension of the steps’ width and the formation of step-bunching. Besides variation of surface diffusion length, the phenomenon described above can be correlated with different dominate modes for the minimization of surface energy at varied growth pressure. Because of the contrary influence of increased C/Si ratio and enhanced step-flow growth on the propagation of BPDs, the dislocation densities of BPDs and threading edge dislocations (TEDs) in epilayers grown at varied pressures remain basically unchanged. The crystalline quality is almost independent of growth pressure based on high resolution X-ray diffraction (HRXRD) measurements.
Highlights
Because of higher power conversion efficiency, 4H Silicon carbide (4H-SiC) devices have benefits in wind turbine power converters [1,2,3], photovoltaic inverters [4,5] and hybrid electric vehicles [6,7,8].Among 4H-SiC devices, 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs) and Schottky barrier diodes (SBDs) with voltage ratings of 1.2 kV and 1.7 kV are the most widely used in power applications
The epilayer surface grown with maximum silane flow rate of 50 sccm is specular with few morphological defects in optical microscope, which demonstrates that gas phase homogeneous nucleation that arises from supersaturation of silicon can be effectively suppressed at low growth pressure
It can be concluded that the growth rate will be elevated further with the increase of precursors flow rates to a certain extent at low pressure
Summary
Among 4H-SiC devices, 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs) and Schottky barrier diodes (SBDs) with voltage ratings of 1.2 kV and 1.7 kV are the most widely used in power applications. Homoepitaxial growth of 4H-SiC layers is a key step in the fabrication of. 4H-SiC power devices since high-quality 4H-SiC epilayers with low defects density, low doping concentration and good morphology are necessary [9]. The most established technique for growth of epitaxial layers of SiC is chemical vapor deposition (CVD) using silane (SiH4 ), and propane (C3 H8 ) as precursors. Epitaxial layers grown at high growth rate on 4◦ off-axis substrates suffer from step-bunching and triangular defects (TDs) [10,11,12]. The formation of triangular defects may be attributed to the larger terrace widths resulting in two-dimensional nucleation [17]
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