Floating‐zone growth of GaAs under microgravity during the D2‐mission

Abstract

A Tc-doped GaAs (100) single crystal of 20 mm diameter and 20 mm length was successfully grown by the floating-zone method during the 2nd German Spacelab mission D2. Dopant striations due to Marangoni convection as well as a reduction of the etch pit density compared to the starting material have been found. The last part of the crystal, grown with the quite high translation rate of 120 mm/h, showed no sign of unstable growth and exhibited properties similar to the parts grown with 3 and 6 mmih.WBhrend der zweiten deutschen Spacelabmission D2 konnte ein tellurdotierter (100) GaAs-Einkristall mit 20 mm Llnge und 20 mm Durchmesser nach der Floating-Zone-Methode gezuchtet werden. Der Kr/stall zeigt Dotierstoffstreifen durch zeitabhangige Marangonikonvektion sowie cine Reduktion der Atzgrubendichte gegeniiber dem Ausgangsmaterial. Der mit der hohen Ziehgeschwindigkeit von 120 mm/h geziiehtete letzte Abschnitt des Kristalls lie8 keinerlei Wachstumsinstabilitlten erkennen und zeigte Materialeigenschaften Bhnlich denen der mit 3 bzw. 6 mm/h geziichteten Bereiche.

The effects of geometry and heating rate on thermocapillary convection in the liquid bridge

“…there are striations in the crystal growth because the oscillation can affect the mass transfer. In space laboratories D-1, D-2 and the sounding rocket, the influence of thermocapillary flow on the process of crystal growth by floating-zone method has been studied (Eyer, Leiste & Nitsche 1985;Cröll et al 1991Cröll et al , 1994. Under the microgravity conditions, it has been proved that striations in the crystal growth are caused by oscillatory thermocapillary flow.…”