Low-leakage MIS structures with 1.5-6 nm CaF2 insulating layer on Si(1 1 1)

Thin high-quality calcium fluorite films are grown on (1 1 1) silicon in the low- and middle- temperature molecular-beam epitaxy processes followed by annealing. Metal-insulator-semiconductor structures with such films exhibit much smaller leakage currents than the casual structures with silicon dioxide. They demonstrate also satisfactory wear-out characteristics. Low leakage is achieved not due to high permittivity, but due to restricted tunnel transparency of the fluorite owing to a large effective mass of carriers. Therefore, CaF2 is a promising candidate for gate material in advanced field-effect transistors.