Growth of large indium phosphide crystals

Abstract

Indium phosphide crystals up to 80 mm diameter and up to 3 kg weight have been grown by the liquid encapsulated Czochralski method, with boric oxide as encapsulant. Polycrystalline indium phosphide was first synthesized by direct reaction between the elements in graphite or pyrolytic boron nitride tubes, enclosed in sealed quartz ampoules. This gives dense polycrystalline ingots in high yield with only a slight amount of free indium. This material is used in the LEC process. Undoped crystals are n-type with carrier concentration of 5 × 10 15 to 1 × 10 16 cm -3. The dominant shallow donor impurities are sulphur and silicon. n-Type crystals have been grown using tin or tellurium as dopants, with carrier concentration up to 4 × 10 18 cm -3, and zinc and cadmium dopants have been used to produce p-type material. Provided that the donor concentration is less than 5 × 10 16 cm -3, then iron doping yields semi-insulating material with a resistivity greater than 10 7 ohm cm, which is thermally stable under epitaxial growth conditions. Etch pit densities for large crystals fall in the range 2–5 × 10 4 cm -2 increasing along the crystal from seed to tail.