Growth of large single-crystal diamond layers: analysis of the junctions between adjacent diamonds

Abstract

In a previous work, the possibility of making large area single crystal diamond layers on top of mosaics formed by two to seven pieces of natural diamonds using MPACVD was demonstrated. The choice of adequate crystallographic orientation of the diamond faces, as well as the identification of the key growth parameters which control the growth mechanism, has lead to the realization of single crystal layers at the junction of adjacent crystals. Although these parameters are necessary, a deeper analysis of layers grown at different junctions shows that they are not sufficient. Additional parameters linked to geometrical adjustment between the crystals significantly influence the crystallographic quality of the layer at the junctions. We report here on a careful analysis of a layer grown on a five-piece mosaic at the junctions between adjacent crystals, where operating conditions favouring the step flow growth mechanism are used. Different types of overlap have been observed. They depend on the crystallographic alignment of the initial diamonds, their difference in height and the direction of the top face misorientation (direction of the step flow), that is on the structure of the original interface. Three types of interfaces have been identified. The first two are obtained when the crystallographic alignment of the two adjacent crystals is less than 1.5°; they differ by the direction of the top face misorientation relative to the highest of the diamonds. The third one corresponds to crystals misaligned by more than 2° and presenting a difference in height. For crystals misaligned by more than 2°, but having exactly the same height, a particular overlap is observed.