DFT Calculations on the Termination of 4H-SiC Non-Polar Surfaces during Photoelectrochemical Pore Formation

In our previous work, single-crystalline porous 4H-SiC thin foils were successfully released from a monocrystalline 4H-SiC wafer by photoelectrochemical etching (PECE). This technology is promising for the next-generation power device fabrication processes (e.g. cost-efficient engineered substrates) and micro-electromechanical systems. The surface terminations of the pore walls will affect the behavior in the further fabrication process and application, thus motivating the need for detailed investigations. This work based on DFT calculations focuses on the surface terminations of five 4H-SiC non-polar surfaces, i.e. {10-10}, {11-20}, {21-30}, {31-40} and {32-50}, which can well represent the walls of the C-face etched pores penetrating through the released foil along the [0001] direction. The surface energies of the stoichiometric surfaces are found to be in the sequence of {11-20} < {32-50} < {21-30} < {10-10} < {31-40}. All these surfaces have high chemical affinity to H₂O and even more to HF. In particular, for the complete surface termination by HF, the relative stability of these crystal planes can be changed and depends on the HF chemical potential. For example, in the range of HF chemical potential from −4.10 to −1.70 eV, the 4H-SiC {10-10} becomes more stable than the {11-20}. This preliminary research provides insight into the surface chemistry of the 4H-SiC non-polar surfaces, especially the {21-30}, {31-40} and {32-50}, which have rarely been investigated.