bJoint Research Center for Atom Technology, Angstrom Technology Partnership (JRCAT-ATP), 1-1-4 Higashi, Tsukuba, Ibaraki 305-0046, Japan

The growth of high quality ZnSe epilayers on Si substrates would allow the integration of ZnSe devices with the silicon integrated circuits. Devices based on the heteroepitaxial growth of ZnSe on Si have been recently demonstrated. However, the efficiency of these devices is largely affected by the high density of crystal defects which are mainly generated at the epilayer/substrate interface. Two serious problems associated to the molecular beam epitaxial (MBE) growth of ZnSe on Si are the 4.3 % lattice mismatch, and the chemical reactions at the interface between these two materials. A thin SiSe_x interlayer at the beginning of the MBE growth is easily formed due to the high reactivity of Se with Si. This layer hinder the smooth growth of ZnSe on Si, resulting in the formation of polycrystalline regions and three dimensional islands at the initial stages of growth. Therefore, the development of new techniques to control the initial stages of growth is necessary in order to improve the performance of ZnSe/Si based devices. In this work we report on the improvement of the crystal quality of ZnSe films on Si(111) by a novel substrate surface treatment with nitrogen prior to the growth. A clean Si(111) surface was obtained by desorbing the surface oxide at ~ 800°C in the growth chamber of a Riber 32P MBE system. Then the temperature was lowered to ~ 600°C, where the Si surface was exposed to a flux of nitrogen free-radicals (N*) with B.E.P. of ~2´10-7 Torr for 10 min. After this treatment the growth was carried out by alternated irradiation of Zn- and Se molecular beams (pulsed MBE) at 230°C. The films evaluated by in-situ reflection high-energy electron diffraction (RHEED), atomic force microscopy, and transmission electron microscopy showed a significant reduction in the density of crystal defects as compared with those grown directly on substrates without the N* treatment.