Electrostatic force microscopy and secondary electron imaging of double stacking faults in heavily n-type 4H-SiC after oxidation

Thermal processing or oxidation of 4H-SiC with n-type doping above about 3×10 ¹⁹ cm ^-3 is known to produce double Shockley stacking faults spontaneously. The resulting region of 3C stacking order acts like a quantum well in the 4H matrix and becomes negatively charged due to modulation doping. Some of these quantum well regions penetrate into the lightly-doped epilayers and intersect the wafer surface as straight lines, due to the 8° misorientation of the wafer from the c-axis. These intersections appear as bright lines in secondary electron images, which we tentatively attribute to increased secondary electron yield due to repulsion of secondary electrons from the negative charge in the quantum wells. Electrostatic force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM) also produce clear images of the quantum well intersections, independent of surface topography. These images are similar to the SEM images.