Abstract
Control of impurity incorporation during crystal growth requires consideration of the relationships between the concentration of the impurity in the liquid phase and its concentration in the growing solid phase. At the solid-liquid interface, the surface space-charge layer in the solid has been found to dominate the incorporation of slowly diffusing impurities. For extrinsic conditions, the amount of slowly diffusing impurity incorporated in the solid varies linearly with the amount in the liquid. Detailed analysis in terms of the surface-space charge layer is given for GaAs liquid-phase epitaxial layers doped with radioactive Te129m. Not only is this linear dependence observed for all the group VI donors S, Se, and Te, but also for the slowly diffusing acceptor Ge. For Te in GaAs, the distribution coefficient goes from greater than unity at low temperatures to less than unity at high temperatures. Rapidly diffusing impurities are not influenced by the surface space-charge layer, and for singly ionized substitutional acceptors or donors the amount of impurity incorporated into the extrinsic solid is expected to vary as the square root of the amount in the liquid. This square-root behavior has been observed for the acceptor Zn which diffuses rapidly in GaAs.
Published Version
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