Relation of Heat Transfer with the Growth Rate of InSb based Bulk Crystals Grown by VDS and its Effect on the Crystal Quality

Abstract

Vertical Directional Solidification (VDS) is a crystal growth technique used to grow the bulk crystals of semiconductor materials by solidification of the melt in the vertical direction. In the growth process, the constituent elements are filled in the quartz ampoule and temperature of the ampoule is raised to a temperature well above the melting point of the constituent elements to obtain the melt. Then the melt is solidified by cooling in the vertical direction from the bottom of the ampoule. Thus it becomes a thermodynamic process where the heat is exchanged between the melt and the surrounding, and the cooling rate depends on the temperature gradient at the solid-melt interface. In the VDS system the temperature gradient can be controlled between 12 °C/cm to 24 °C/cm. Estimation of heat exchange during the growth process, using the concept of enthalpy indicate that, for the crystal growth of InSb by VDS technique, the growth rate must be less than 9 mm/hour when the temperature gradient is 20 °C/cm. Indium antimonide (InSb) is a narrow-band gap semiconductor material obtained from the elements of III-V groups indium (In) and antimony (Sb). Among all the III-V binary semiconductors InSb is the most studied semiconductor because of its narrow energy band gap (0.17 eV). Considering importance of bulk semiconductors, InSb based crystals (ingots) were grown by VDS technique at different temperature gradients in the range of 12 °C/cm to 24 °C/cm. The grown ingots were sliced to ~ 500 µm thick wafers for the characterization. Results show that the crystals grown at low growth rate (~ 3 mm/hr) are good quality single crystals with maximum mobility up to 44500 cm2/V∙s at room temperature (300 °C).