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ATOMIC DIFFUSION WITH STRAIN AND INJECTION J.A. Van Vechten Center for Advanced Materials Research, Department of Electrical and Computer Engineering, Oregon State University, Corvallis, OR 97331-3211 U.S.A. ABSTRACT The inherent complexity of defect processes in III-V's and the consequent A difficulties with ab initio and semi-empirical methods are recalled. potential solution using massive Monte Carlo simulation on microcomputers is suggested. Evidence for the validity of the Ballistic Model, BM, of atomic diffusion in III-V's is noted. According to the BM the effect of strain (in the absence of any electrostatic, population, or recombination effect) is to increase the rate at which a given mobile atom hops where the sample is compressed. For the case of misfit strain at a (100) junction, we note that the anisotropy of the elastic constants implies that some planes running into the bulk will be compressed whichever the sign of the misfit. This implies that misfit strain of either sign should increase the observed rate of We also recall the interdiffusion, in the absence of other effects. importance (demonstrated at low T) of recombination enhancement of atomic diffusion, RED. Devices are processed at temperatures where the thermal rate of recombination is very high and often operated at high levels of injection. The interaction of strain with RED is clearly important and complicated. The III-V crystals have the further complication of being piezoelectric. active piezoelectric axes are , so a pure strain does not produce However, the accommodation a device makes to misfit at (100) a field. junctions can generate a strong field, which may fluctuate with bias voltage. PROBLEMS WITH III-V's Recognizing the inherent complexity [1] of defect formation, interaction, migration and reaction processes in a semiconductor, author has concluded that neither ab initio calculations nor traditional semi-empirical methods are likely to make further sense of the vast array of raw data or to hasten the development of useful products. Complexity arises in a semiconductor because the band gap allows each species to have multiple ionization levels and allows sharp gradients of the Fermi level, EF. These complexities are particularly acute in III-V devices because: i) Unlike the elemental crystals, C, Si and Ge, wide deviations from stoichiometry are present [2] in the materials used to make III-V devices. E.g., EL2 is produced in GaAs by deliberately growing ii) Two types of vacancy, V, occur and, probably as a it As rich [3,4]. consequence of the deviations from stoichiometry, are much more abundant [5] than in Si. iii) Anti-site defects of both types are abundant (while they are iv) The band gap is absent in the elemental crystals and few in II-VI's). generally larger than in corresponding IV-IV crystals and there is less self compensation than in II-VI's. Thus, E ranges past more ionization levels. v) Because of the abundance of ionizeJ species and the moderate dielectric constant, these species are almost never found as isolated p