Physical vapor transport revisited

Using iodine as transport species and octofluorocyclobutane (C4F8) as inert background gas, physical vapor transport rates in horizontal cylindrical ampoules were accurately measured over a wide range of well-defined ampoule filling and thermal boundary conditions. Nonlinear axial temperature distributions were applied that minimized multiple crystal nucleation. Ampoule filling conditions were chosen that resulted in the dominance of either compositionally or thermally driven convection. Three-dimensional numerical modeling of the transport process yielded quantitative agreement with measured transport rates. Analysis of the calculated flow and concentration fields reveals the physical reasons for the failure of the various two-dimensional models to reproduce the experimental results.