Silicon carbide (SiC) is a wide-band gap semiconductor and one of the more promising materials for use in high-temperature high-power devices because of its thermal, chemical, and mechanical stability. Still, there are obstacles to its fabrication as epitaxial films because it requires a high substrate temperature (around 1500°C), and it's hard to control the polytype that grows--usually a mixture is obtained. These polytypes represent variations in the stacking of the SiC layers, and because they alter the band gap of the material, finding a method to control the growth is vital.
Kusumori et al. have developed a pulsed laser deposition technique for fabricating heteroexpitaxial films of the 3C, 2H, and 4H polytypes with a substrate temperature of only 1100°C. Unlike other deposition methods, laser ablation ejects species containing considerable kinetic energy, which is converted to thermal energy on impact with the sapphire substrate. Thus, by altering the frequency of the laser pulses it is possible to raise the temperature at the site of deposition while keeping the rest of the substrate at a lower temperature. As they varied the laser pulse frequency from 1 to 2 to 5 Hz, the polytype changed from 3C to 2H to 4H. -- MSL
Appl. Phys. Lett. 84, 1272 (2004).
