Double crucible LEC growth of In-doped GaAs using inner crucibles with a bottom tube

Abstract

In order to reduce InAs segregation along In-doped GaAs single crystals, the liquid encapsulated Czochralski (LEC) process commonly used for GaAs was modified, by using an improved double crucible technique and the concept of zone leveling. This avoided the long-existing dilemma of the double crucible technique: the hole in the inner crucible either is too small to let the replenishing melt go through or too large to suppress mixing between the growth melt and the replenishing melt through the hole. A tube was provided at the bottom of the inner crucible; its 6 mm inside diameter was large enough for the replenishing melt to pass through without being blocked by B 2O 3, and its 70 mm length was more than long enough to suppress mixing. The initial growth melt was leveled (enriched) to C o/ k, where C o is the targeted crystal composition of 0.04 mol% InAs and k is the effective segregation coefficient 0.116. Effective segregation reduction was obtained and a crystals was grown with a uniform InAs concentration of 0.0422±0.0024 mol% InAs. A similar crystal was grown by using the conventional LEC process; the InAs concentration rose monotonically from 0.0463 mol% at the starting end to 0.245 mol% at the finishing end.