Segregation and interface stability in germanium-silicon single crystal alloys

Abstract

Melt growth allows large-scale production of semiconductor crystals. However, growth of Ge-Si single crystals from melt is extremely sensitive to experimental parameters. Obtaining accurate thermal data near the solid/liquid (s/l) interface and so knowing the uid ow characteristics during Ge-Si alloy crystals are essential to control the growth, which is not easy with conventional techniques. Especially, because of widely varying segregation coe cient, large density di erences, and large solidi cation range in the case of Ge-Si growth, it is di cult but important to keep the interface planar at a constant temperature to avoid compositional uctuations that may lead to interface instability and degradation of single crystallinity. The use of a crystal growth technique called axial heat processing (AHP) to grow single crystal semiconductor alloys from the melt is investigated. The technique includes an immersed ba e which distributes the heat over the entire growth interface, decreases the melt height, and divides melt into two regions. This consequently reduces the buoyancy driven convection in the melt, induces forced ow, and continuously supplies fresh charge to the growth domain. Five and twelve atomic percent silicon doped germanium single crystals have been grown by the AHP method at 0.75 and 2 mm/h velocities with two di erent melt heights (5 mm and 10 mm). Few Bridgman crystals have also been grown to set a base for a comparison between the crystals grown by the AHP and Bridgman techniques.