Real-Time Measurements of Stress Relaxation in Heteroepitaxy

Prof. R. Beresford

Division of Engineering, Box D, Brown University, Providence, RI 02912, USA

The multibeam optical stress sensor technique has been shown to provide accurate real-time measurements of the stress-thickness product during MBE growth of InGaAs on GaAs. Since the thickness vs. time relation can be well calibrated in MBE, the stress sensor experiments yield plots of the strain relieved vs. film thickness during growth, as well as the strain relieved vs. time during annealing (growth interrupts). A body of evidence is being assembled for the behavior of In_xGa_1–xAs films with x@0.15, which relax via the generation and motion of dislocation lines. The strain relief has been studied as a function of temperature during continuous growths at typical rates of around 1 monolayer per second. The relaxation behavior is richer than expected, and does not appear to follow "bulk-like" kinetics based on dislocation multiplication and thermally-activated glide. The data suggest an alternative kinetic description based on the rate of emission of dislocation density from an areal distribution of sources, which become deactivated as the back-stress from emitted dislocation lines reduces the local excess stress. Concurrently, studies of the relaxation behavior during growth interrupts reveal that at a given dislocation density, the glide velocity can be increased orders of magnitude by the presence of the growth flux. These results are interpreted in terms of adatom-enhanced nucleation of single kinks at the growth surface. Applications of this work to the growth of "metamorphic" InAlAs buffer layers will also be discussed.