Single crystal growth of germanium - silicon alloys

Germanium-silicon (Ge-Si) alloys enjoy a widespread interest because of their remarkable potential for optoelectronic, solar cell, thermoelectric power generation, and photodetector applications. Despite this obvious interest, Ge-Si crystal growth has difficulties. Ge-Si alloy system is extremely prone to segregation due to its thermo-physical properties. This prevents the growth of quality bulk crystals of Ge-Si, which are the basis for example for solar cells as wafers. A new bulk crystal growth technique called axial heat processing (AHP) is proposed to alleviate the adversities during Ge-Si single crystals. The technique makes use of an immersed baffle that spreads the heat over the growth interface, decreases the melt height, and divides melt into two regions. Several silicon doped germanium single crystals with 5 and 12 atomic percent concentration have been grown by the AHP method at 0.75 mm/h and 2 mm/h velocity with two different melt heights. Few Bridgman crystals have also been grown to set a base for a comparison between the crystals grown by the AHP and Bridgman techniques. The effect of the processing variables on the longitudinal and radial dopant distribution and single crystal quality is investigated. A new theoretical approach is also proposed to predict the solute redistribution and morphological stability in the grown crystals. The predictions of this new model are found to be superior when compared to those of Constitutional Supercooling (CS) and Mullins and Sekerka (MS) criteria.