Crystalline quality of highly oriented diamond films grown on <100>silicon studied by conventional TEM

Two diamond films grown in a highly oriented way on [100] Si have been synthesised using a MPCVD process and observed by TEM to study their crystalline quality. The observation of plan view thin foils taken at different altitudes in the films allows to show up an evolution of the nature and the spatial distribution of structural defects (dislocations and planar defects) present in the crystals constituting the studied films. We define thus a critical thickness, which depends on synthesis parameters, nucleation density and proportion of oriented nuclei, and below which the crystalline quality is restricted by the presence of misoriented crystals and crystalline volumes filled with planar defects. Above that critical thickness, these disturbances disappear, leading to films presenting a high crystalline quality, only limited by dislocations and quite clean grain boundaries.