5.5: SELENIDES

5.5 SELENIDES

Thin films of selenides such as ZnSe are prepared by rf sputtering from a ZnSe cathode in an Ar atmosphere. Typical sputtering conditions are shown in Table 5.52.[3] In the rf-sputtering system, the anode is perforated and substrates are placed behind the anode at floating potential to reduce the effects of the high-energy sputtered atoms and secondary electrons from the cathode.

Transmission electron diffraction patterns from ZnSe layers sputtered onto the (100) plane of NaCl single crystals exhibit the polycrystalline or epitaxially grown monocrystalline phase shown in Fig. 5.142. The monocrystalline films consist of a single phase of cubic-ZnSe structure with the (100) plane parallel to the NaCl surface, but the polycrystalline films consist of two phases, a cubic ZnSe structure and a hexagonal ZnSe structure. The degrees of structural ordering depend on deposition rates and substrate temperatures as shown in Fig. 5.143. In this figure, a minimum epitaxial temperature T _c was found to exist for a given deposition rate R, and the exponential relationship R = A exp(- Q _d / kT _c) was obeyed for epitaxy. Here, A