A high temperature high purity source for metal beam epitaxy

Abstract

We report the first use of modulated beam mass spectrometry to assess the purity of metal beams generated from two types of Knudsen effusion oven used in metal beam epitaxy. One of these types contained sapphire components in contact with tantalum heater windings. In this case considerable contamination of gold and silver beams by Al 2O and aluminum was observed over the temperature range 1000–1400°C. Thermodynamic considerations support the view that these contaminants originated from contact reduction of the sapphire by the tantalum metal. The condensation of these impurities on an (001) indium phosphide surface at not greater than 40°C was detected by Auger electron spectroscopy. In the second type of oven all oxide components were replaced by pyrolytic boron nitride and the tantalum windings by molybdenum windings. Gold and silver beams generated from this oven were of high purity with no detectable oxide species or other beam contaminants. Aluminium beams contained Al 2O as a transitory beam impurity due to atmospheric oxidation of the aluminium charge prior to loading. The implications of the beam impurities from the first type of source are discussed, and the performance of the second type of source in generating epitaxial silver, aluminium and gold films on indium phosphide at growth temperatures not greater than 40°C is reviewed.