Transient convection of Te doped GaSb induced by g-jitter

Abstract

Gallium antimonide (GaSb) is commercially used for solar cells and thermophotovoltaic devices. It is also used as a substrate material for the epitaxial growth of heterostructures, which are used for optoelectronic applications. The semiconducting properties of the material are governed by an antisite defect that requires compensation by a donor dopant such as tellurium to provide n-type conductivity. The electronic and optical properties of Te doped GaSb are greatly influenced by the degree of Te segregation in the crystal. The latter is strongly affected by buoyancy and thermocapillary (Marangoni) driven convections. Both types of convections are associated with a temperature-induced density and surface tension gradients along the sample. During 1996 and 1997, nine microgravity experiments were conducted on the MIR space station to determine the segregation of dopants during microgravity crystal growth using the QUELD furnace on the microgravity isolation mount. The space-grown samples displayed fluctuations in [p] and hence in [Te] attributed to g-jitters events and not to Marangoni convection during crystal growth (J. Vac. Sci. Technol. A 18(2) 2000). On the numerical side, attempts were made to study the effect of convection and the g-jitter on the segregation of Te in terrestrial and in microgravity conditions. Since no data of the g-jitter were available during the experiment attempt is made to study the transient convection due to the two different types of g-jitters. In the first case, the time dependent gravity was introduced in the momentum equations. In the second case, the time dependent velocity was implemented at the boundary of the quartz sample. The full Navier–Stokes equation combined with heat and mass transfer equations were solved numerically using the finite element techniques. The results show that g-jitter and time dependent velocity applied at the quartz wall play an important role in segregation of tellurium in the melt. A detailed parametric study was performed in order to reveal the convection pattern under various conditions.