Silicon Induced Mixing of AlGaAs Superlattices – Behavior and Mechanisms

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Abstract
Mixing (or interdiffusion) of AlGaAs superlattice layers is greatly accelerated in the presence of Si doping. We have employed secondary ion mass spectrometry (SIMS) to monitor the depth dependence of the Al diffusion coefficient as well as the Si diffusion profile. Our results reveal unusually complex dependences on implantation and annealing conditions. To isolate the effects of chemistry and lattice damage, several structures were grown by molecular beam epitaxy (MBE) containing plateaus of Si concentration. The doping dependence and activation energy of Al diffusion were then evaluated in as-grown samples and in samples damaged by MeV Ga ion bombardment. To further elucidate the process, samples containing single or multiple implants of various dopants and impurities were examined. Microscopic and electrical characterizations were also performed. Al diffusion was found to be strongly inhibited by lattice damage and by very high Si doping levels. The Al diffusion coefficient has a high power law dependence on Si concentration while its activation energy is relatively unaffected by doping or lattice damage. A wide range of experimental and theoretical mixing studies are surveyed. Mixing models invoking Si pairs, divacancies, Fermi level arguments, and other mechanisms are critically assessed.