| Reflection high-energy electron diffraction (RHEED) is the principal in situ analytical tool used during molecular-beam epitaxy (MBE). The layer-by-layer growth, with alternate roughening and smoothing of the surface, causes RHEED intensity oscillations to occur with a period equal to a monolayer deposition time. Because the substrate azimuth greatly affects the reflected intensity, it was thought that RHEED could not be used for real-time monitoring of MBE growth of device wafers, since these are rotated to insure uniformity.; A technique has been developed that allows the measurement of RHEED oscillations while the wafer is rotating. High-speed ({dollar}>{dollar}100 rpm) substrate rotation is used in combination with gated detection. As an added benefit, a larger number of oscillation periods are observed with this technique than during stationary measurement because of the much higher growth rate uniformity across the sample.; The rotating measurements also showed that the average over all wafer azimuths of the RHEED specular intensity exhibits the same oscillations. This has allowed the replacement of the gated detection system by an averaging detection method; consisting of a low-pass filter to suppress the fast signal variations due to rapid changes in azimuth, but not the low-frequency ({dollar}<{dollar}1 Hz) growth related oscillations. This considerably simplifies the detection system and at the same time reduces noise related to wafer motion, 60 Hz, etc. These techniques have potential use for real-time monitoring of layer thickness and composition.; The phenomenon of RHEED oscillations is also investigated theoretically. A new one-dimensional growth model describing the evolution of a random sequence chain of plateaus is developed. The diffraction problem for this model surface, including adatoms, is solved in the kinematical approximation. The model identifies the well-known fast initial intensity rise during recovery as being due to disappearing adatoms. Instrumental broadening is taken into account analytically, removing the need for separate numerical convolution. A model of dynamical scattering for perfectly ordered surfaces is also presented. The effect of multiple scattering on RHEED oscillations is discussed and approaches are described to maximize the kinematical character of the specular intensity. |
