Axial and shear stress in nitrogen-doped homo-epitaxial chemical-vapor-deposition diamond films

Abstract

Control of residual stress in diamond is crucial to improve the spin dephasing time (T2*) of nitrogen-vacancy centers for quantum applications. When the surface of a substrate used for homoepitaxial growth is crystallographically tilted at a slight angle away from a major crystal plane [e.g., (001)], the atomic structure of the surface at the homoepitaxial growth front changes, which in turn alters the homoepitaxial growth mode. As a result, the incorporated stress in the homoepitaxial diamond layer is also likely to vary. In this study, we investigated the effect of the substrate inclination-direction in the (001) plane, the so-called inclination-direction, on the residual stresses. The 400 μm-thick nitrogen-doped (001) diamond films were grown on the substrates with different inclination-directions, a [110] or a [100]. Mapping of the stress tensor revealed that the inclination-direction alters the nature of the residual stress: the [110] inclination-direction led to a dominant gradient in the axial stress (σxx + σyy + σzz) along the [001] direction, whereas the [100] inclination-direction led in shear stress (σxy, σyz, and σzx). Although the nature of the residual stress changed with the inclination-direction, the mean values of the measured T2* were comparable for both samples (1.25 μs for [110] and 1.26 μs for [100]). This result was consistent with the fact that the dephasing rate due to the stress in the CVD diamond film (0.25 MHz for [110] and 0.26 MHz for [100]) was comparable.