Accuracy of AlGaAs Growth Rates and Composition Determination Using RHEED Oscillations
Todd E. Harvey, Kristine A. Bertness, Robert K. Hickernell, C. M. Wang, Jolene D. Splett
We investigate the sources of uncertainty in the measurement of the reflection high-energy electron diffraction (RHEED) intensity oscillations during growth of AlAs, GaAs, and AlGaAs on GaAs substrates, and the resulting effects on predicted growth rates and composition. Sources of error examined include beam positioning, flux transients, substrate size, 'beat' phenomena in the RHEED oscillations, substrate temperature, and incident beam direction. We find that flux transients and flux nonuniformity are the dominant systematic errors in predicting growth rates and composition with RHEED. From flux uniformity measurements,we estimate the beam positioning error for our growth system to be 0.2-0.6%/mm, and substrate size to impact the uncertainty by as much as several percent. In addition to these errors, flux transients can cause an uncertanty of up to 1%. We also present a procedure that uses the measured variance in the growth rates to calculate the composition with the smallest mean square error.