Effect of crystal shape on etch-pit-density distribution in undoped low dislocation density GaAs crystals grown by the As-ambient liquid encapsulated Czochralski technique

Abstract

The dislocation density for conventional liquid encapsulated Czochralski (LEC) GaAs crystals such as those of 3–4 inch in diameter is too high to clarify the dislocation generating conditions. Therefore, growing almost dislocation free crystals and clarifying the dislocation generating conditions individually is necessary before the crystal size is enlarged. To reduce the dislocation density, crystals were grown by the As-ambient LEC (As-LEC) technique under low temperature gradient along the pulling direction. An etch pit density (EPD) at the center of the 20 mm diameter crystal of the order of 10 3 cm −2 was obtained. The EPD distribution and crystal shape in the pulling direction correlate for low EPD crystals and show that crystal shape control is necessary for obtaining lower EPD crystals. The EPD distribution perpendicular to the pulling axis, however, exhibited the so-called “W”-shape. Even though the temperature gradient along the pulling axis was reduced, dislocations which were considered to be generated by excessive radial thermal gradient, remained in the crystals.