Thickness Impact on the Morphology, Strain Relaxation and Defects of Diamond Heteroepitaxially Grown on Ir/Al₂O₃ Substrates

This paper investigates the formation and propagation of defects in the heteroepitaxial growth of single-crystal diamond with a thick film achieving 500 µm on Ir (001)/Al₂O₃ substrate. The growth of diamond follows the Volmer–Weber mode, i.e., initially shows the islands and subsequently coalesces to closed films. The films’ strain imposed by the substrate gradually relaxed as the film thickness increased. It was found that defects are mainly located at the diamond/Ir interface and are then mainly propagated along the [001] direction from the nucleation region. Etching pits along the [001] direction formed by H₂/O₂ plasma treatment were used to show defect distribution at the diamond/Ir/Al₂O₃ interface and in the diamond bulk, which revealed the reduction of etching pit density in diamond thick-film surface. These results show the evident impact of the thickness on the heteroepitaxially grown diamond films, which is of importance for various device applications.