REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION INTENSITY OSCILLATIONS DURING MOLECULAR-BEAM EPITAXY ON ROTATING SUBSTRATES

We report the gated detection of reflection high-energy electron diffraction (RHEED) signal intensity oscillations during molecular-beam epitaxy (MBE) while the wafer is being rotated at high speed (>100 rpm). In general, a larger number of oscillation periods are observed with this technique than during stationary measurement because of the very high growth rate uniformity across the sample. We found that the average over all azimuths of the RHEED specular spot intensity shows the same growth induced oscillations. This allowed us to replace the gated detection by an averaging detection method: a low-pass filter suppresses fast variations due to rapid changes in azimuth, while passing low-frequency (<1 Hz) growth related oscillations. This simplifies the detection system and at the same time reduces noise related to wafer motion, 60 Hz, etc. These techniques have potential use for in situ monitoring of thickness and composition of device wafers.