Silicon carbide (SiC), as a wide-bandgap semiconductor material, is highly valued for its exceptional performance in high-power, high-frequency, and high-temperature electronic devices. During SiC epitaxial growth, the silicon face (Si-face) is typically chosen over the carbon face (C-face) as the growth surface. This preference is not incidental but is based on the significant differences in the physicochemical properties of the two surfaces, with Si-face epitaxy better meeting the industrial requirements for high-quality epitaxial layers. This article systematically discusses the reasons behind this choice from the perspectives of surface energy and chemical activity, epitaxial growth rate, surface morphology and crystal defects, interface properties, and industrial practice.

1. Differences in Surface Energy and Chemical Activity

The Si-face and C-face of SiC exhibit fundamental differences in surface energy and chemical activity, which are key factors influencing their epitaxial behavior.

Si-face:

The Si-face has a lower surface energy and relatively weaker chemical activity, making it more stable. This characteristic allows precursor molecules to adsorb and diffuse uniformly during epitaxy, forming a regular step-flow growth mode and resulting in smooth epitaxial layers. Moreover, the lower surface energy reduces nucleation uncertainty during growth, helping to minimize defect formation.

C-face:

The C-face, with higher surface energy and stronger chemical activity, reacts more readily with precursors in the gas phase. Although this high chemical activity can accelerate the growth rate, it also leads to rough and irregular growth structures, increasing defect density.

2. Epitaxial Growth Rate

The differences in epitaxial growth rates on the Si-face and C-face are significant.

Si-face: The moderate chemical reactions on the Si-face result in a lower and more uniform growth rate, facilitating precise control over the epitaxial thickness. This growth mode is ideal for producing epitaxial layers with stringent thickness and quality requirements, such as the 4H-SiC layers used in high-power electronic devices.

C-face: The higher chemical reactivity of the C-face leads to a significantly faster growth rate. However, excessive growth rates often induce amorphous or polycrystalline structures, and irregular step-flow growth is exacerbated. This phenomenon poses challenges for controlling the thickness and crystal quality of the epitaxial layers.

3. Surface Morphology and Crystal Defects

The surface morphology and defect density of the epitaxial layers directly impact device performance, with Si-face growth exhibiting clear advantages in these areas.

Epitaxial layers grown on the Si-face:

Si-face epitaxial layers typically feature smooth surfaces and regular step structures, with low surface roughness and uniform morphology. This growth mode reduces the density of crystal defects, including dislocations and stacking faults, thereby enhancing the stability and reliability of device performance.

Epitaxial layers grown on the C-face:

C-face epitaxial layers tend to have irregular step structures and higher surface roughness. Additionally, the high chemical reactivity of the C-face makes interface reactions and mismatches more likely, further increasing defect density.

4. Interface Properties

The interface characteristics between the epitaxial layer and substrate play a decisive role in determining the crystal quality and performance of the final device.

Si-face interface:

The Si-face interface is smoother and better suited for maintaining lattice matching in the epitaxial layer, reducing grain boundary defects and interface stress. This feature is critical for achieving large-area, high-quality epitaxial growth.

C-face interface:

The high chemical activity of the C-face complicates the interface reaction during epitaxial growth, making chemical and structural mismatches more likely. This leads to an increase in interface defects, adversely affecting the overall performance of the epitaxial layer.

5. Industrial Practice and Application Demands

Si-face epitaxial technology has been widely adopted in industrial applications. Its mature processes reliably produce high-quality epitaxial layers that meet the demands of high-power and high-frequency electronic devices. In contrast, while the C-face may offer potential advantages in specific applications, such as field-effect devices requiring higher carrier mobility, its complex growth processes and difficulties in quality control have limited its widespread adoption.

Conclusion

In summary, the preference for Si-face over C-face in SiC epitaxial growth is driven by the inherent differences in their physicochemical properties. The low surface energy and moderate chemical activity of the Si-face enable the stable growth of high-quality epitaxial layers, while minimizing crystal defects and interface stress, meeting the technical requirements for industrial-scale production. Conversely, the high chemical activity of the C-face, though advantageous in certain respects, complicates growth control and results in lower-quality epitaxial layers, restricting its broader application. Thus, selecting the Si-face as the epitaxial growth surface has become the best practice in current SiC epitaxial technology.

Related product links

Epitaxial Wafer

Silicon Carbide Wafer (SiC Wafer)