Practical aspects of solid source molecular beam epitaxial growth of phosphorus-containing films

Abstract

The growth of phosphide films by solid source molecular beam epitaxy presents challenges in regard to safety, oxygen contamination, and disposal of residual phosphorus. Upon venting the growth chamber after phosphide growth, phosphine concentrations greater than the permissible exposure limit were measured inside the chamber due to the reaction of moisture with residual red phosphorus deposits on the chamber walls. Another product of the reaction is hydrated phosphorus oxides that can degrade subsequently grown aluminum-containing films. Procedures were developed to safely vent the growth chamber as well as to minimize oxygen contamination of phosphide and arsenide films. Contamination in the phosphide films was also caused by significant concentrations of oxygen in the bulk of the starting phosphorus ingot. The contamination was greatly reduced by lowering the phosphorus cracker temperature. A mechanism involving volatile phosphorus trioxide, P4O6, is proposed to qualitatively explain the effect of cracker temperature on oxygen contamination. Due to incomplete cracking of sublimed elemental phosphorus, deposits of flammable white phosphorus were created in the chamber. Procedures were developed to safely remove the white phosphorus from the machine and convert it into a nontoxic form for easy disposal.