Heat Exchanger Method (HEM) grown GaAs single crystals and their homogeneity

GaAs single crystals, 32 mm in diameter and 32 mm in length, were grown by the heat exchanger method (HEM). A 〈111〉 seed crystal was used with helium gas for the heat exchanger. The optimum conditions for single crystal growth were determined to be growth time of 8.5 h, growth rate less than 4 mm/h and a helium flow rate smaller than 23.6 l/min. The Hall effect was measured by the Van der Pauw method about the radial and axial directions. From this measurement the homogeneity was known, and the Hall mobility and carrier concentration at room temperature were found to be 4580 cm²/V·s and 3.5×10¹⁶ cm^-3, respectively. An EPD measurement was made to investigate the crystal quality. The value was 2×10³ cm^-2 at the center, but increased toward the edge to a value of 1×10⁴ cm^-2.