The Growth and Properties of Large Semi-Insulating Crystals of Indium Phosphide

Abstract

Semi-insulating crystals of indium phosphide have been grown with diameters up to 80 mm and weight up to 3 kg using the liquid encapsulated Czochralski (LEC) process 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 excess of free indium. This material is used in the LEC process.

Undoped crystals are n-type with carrier concentrations of 5 × 10^15–1 × 10¹⁶ cm^-3. The dominant donor impurities are sulphur and silicon. Provided that the donor concentration is less than 5 × 10¹⁶ cm^-3 the iron doping yields semi-insulating material with a resistivity greater than 10⁷ ohm-cm, which is thermally stable under epitaxial growth conditions. Etch pit densities for large iron-doped crystals fall in the range 2–5 × 10⁴ cm^-2, increasing along the crystal from seed to tail.