Interface control epitaxy of ionic crystal and covalent crystal by means of ionicity control layer

For heteroepitaxial growth of covalent crystals and ionic crystals which have very different ionicities, a new approach of inserting a material which has intermediate ionicity to the heterointerface for the purpose of accommodation of the large ionicity difference was proposed.

For the case of growth of fluorides on various semiconductor substrates, it was found that the epitaxial temperature of fluoride becomes lower with decreasing the difference of ionicity between the fluoride and substrate. It was found that ionicity has relationship with the surface energy which had been used to discuss the wettability of dissimilar materials heteroepitaxy. To make sure the relationship between ionicity and wettability, the contact angle measurement of ZnSe and GaAs islands grown on CaF, was carried out using AFM. As a result, it was also found that the wettability of semiconductors on the Caf, would be improved when ionicity difference was smaller It was indicated that ionicity plays a role in these problems, and it was suggested that accommodating ionicity difference by inserting a layer which has intermediate ionicity was effective to make good heterostructure I

In order to prove it, the insertion of thin ZnSe layer to GaAs/CaF, interface was studied using MBE method. As a result, the crystallinity of GaAs layer was successfully improved compared to that in the case of direct growth on CaF, Investigation of the ZnSe layer was carried out in order to make clear the effect, through interface characterization by means of SIMS, RHEED and AFM. It was confirmed that ZnSe layer stayed at the interface and acted as a buffer layer. It was found that by inserting this ZnSe layer. GaAs crystallinity at initial growth stage was improved, and the good crystallinity could suppress diffusion of Ca and F to the GaAs layer, and that GaAs nucleation density was increased on the ZnSe laver These phenomena were suggested to be the important effect of insertion of ZnSc layer into GaAs/CaF, iterface