The surface reaction mechanism in MOMBE‐ALE of ZnSe and CdSe using DMZn, DMCd, and H2Se as reactants is studied with a newly developed optical in‐situ monitoring method. The new method is named surface photo‐interference (SPI), because the concept of the SPI is essentially concerned with a photo‐interference in the heteroepilayer. Fairly low‐energy photons for which the epilayer is transparent can be used as probing light in SPI. Reflecting this feature, SPI is especially useful for studying heteroepitaxial growth kinetics of wide‐gap II‐VI compounds, because the effect of photocatalytic growth rate enhancement can be avoided when using such low energy photons as probing light. It is shown that there is a quite significant difference in the surface reaction mechanism between the MOMBE‐ALE of ZnSe and CdSe. That is, in the ALE of ZnSe when none of the source gases are per‐cracked, the reaction to form ZnSe can take place when the group‐II source (i.e., DMZn) is supplied, resulting in an alternate appearance of Zn terminated and H2Se terminated surfaces during growth. On the other hand, the reaction to form CdSe can do when the group‐VI source (i.e., H2Se) is supplied, resulting in an alternate appearance of Se terminated and DMCd terminated surfaces during growth.
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