Growth and characterization of heteroepitaxial (001) and (111) diamond on Ir/sapphire structures

We report the comparative study on the growth and characterization of heteroepitaxial (001) and (111) diamond on Ir/(112¯0) and (0001) sapphire using direct current plasma chemical vapor deposition, in order to understand differences in heteroepitaxial behavior in both crystal directions as a preliminary step for large-sized high quality heteroepitaxial (111) diamond growth. An Ir deposition and bias-enhanced nucleation treatment were followed by 60, 190, and 1500 s diamond growth, under the same process conditions. The growth behaviors, morphological, and structural properties of the two crystal directions were greatly different. The growth rates of (001) and (111) diamond were 500 and 60 nm/min, respectively. The epitaxial relationships of (001) and (111) diamond were confirmed to be (001) diamond//(001) Ir//(112¯0) sapphire and (111) diamond//(111) Ir//(0001) sapphire. Further, in-plane relationship of (001) diamond was [1¯10] diamond//[1¯10] Ir//[11¯00] sapphire. In the case of (111) diamond growth, 180°-rotated twins and penetration twins in diamond were observed. The atomic force microscopy and X-ray rocking curve measurements exhibited that the surface roughness and the crystalline quality of (111) diamond were inferior to those of (001) diamond. Consequently, the growth conditions of Ir and diamond in [111] direction need to be considerably modified for suppressing twins and surface roughening and obtaining a high growth rate and high crystalline quality.