Maskless epitaxial overgrowth of diamond on 3D patterns formed by self-organization in an oxidation process

Reduction of the dislocation density (DD) in heteroepitaxial diamond quasi-substrates by maskless epitaxial overgrowth on 3D-patterned surfaces is reported. To create structures appropriate for maskless overgrowth, three different approaches were explored. First, CO2/H2 etching in a microwave plasma chemical vapor deposition setup was applied to generate dislocation induced pits. Even for high etch depths of 182 μm, pits with the shape of inverted pyramids aligned along ⟨110⟩ remained rather small (≈10−6 cm2). In the second approach, dry oxidation in a furnace using synthetic air provided structures of suitable size (>10−5 cm2) but insufficient depth. Finally, moisturizing the feed gas reduced the etch velocity by a factor of ≈7, but also produced ⟨100⟩ oriented pits with both high facet angles of ≈35° and large areas of up to >10−4 cm2. Subsequent maskless overgrowth resulted in a reduction of the initial DD by more than one order of magnitude down to 1.7 × 106 cm−2. Repetition of the etching/overgrowth sequence is expected to facilitate further improvement. The novel technique of self-organized 3D pattern formation is applicable to as-grown surfaces without the need for polishing and lithography. It provides a simple, robust, and scalable concept to improve the structural quality of diamond wafers.