Heteroepitaxy of Cd-Rich CaxCd1-xF2 Alloy on Si Substrates and Its Application to Resonant Tunneling Diodes

Abstract

Epitaxial growth of Cd-rich CaxCd1-xF2 alloy with small composition x on Si(111) substrates was investigated in order to obtain improved fluoride resonant tunneling diodes (RTDs). The direct growth of CdF2 on Si substrates was studied from the viewpoint of surface roughening and sticking coefficient, and it was revealed that the origin of growth instability of CdF2 was the direct reactivity of CdF2 with Si. This phenomenon was controlled by addition of a small amount of CaF2 to CdF2, forming a Cd-rich CaxCd1-xF2 alloy. It was found that the growth temperature of Cd-rich CaxCd1-xF2 on bare Si at which apparent re-evaporation was observed was higher than that of pure CdF2, and that the surface roughness of the layers grown at room temperature on thin CaF2 buffer layers was reduced by the addition of only 5% CaF2 to CdF2. Furthermore, RTDs using the Cd-rich CaxCd1-xF2 layer for the quantum well layer were fabricated, and stable operation and improved characteristics were obtained compared to the conventional RTDs using pure CdF2 layers.