Interface contamination by suboxide transport

Evidence is presented to suggest that unintentional concentrations of silicon, germanium, and aluminum at gallium arsenide film substrate interfaces are transported as suboxides. A thermodynamic treatment is used to conclude that arsenic oxide, desorbed from substrates, provides the oxygen for suboxide formation in the vicinity of effusion cells. Silicon and germanium suboxides can then be reduced by gallium on substrate surfaces. Reduction of aluminum suboxide is thermodynamically unfavorable, thus, oxygen is incorporated with the aluminum. An approximate value of 68.4 entropy units results from the analysis for the process As4⇔2As2. This value has not been previously reported.