ULTRA-HIGH PURITY ARSENIC FOR MBE

A requirement for high purity elemental arsenic for use in compound semiconductors has become well established. The capabilities of molecular beam epitaxy as a fabrication technique are best exploited if the arsenic used has particular additional features. Prominent among these are a uniform distribution of impurities at levels down to 10 ppb, and a geometrically uniform distribution of material in the charge used. Once material such as this, of 7N purity or better, emerges from its processing, a major vulnerability is from recontamination. Prevention of this is a further important requirement. Detailed examination of possible process strategies has led to an approach targeted on the manufacture of solid arsenic "charges" especially suited for MBE application. Factors involved are reviewed. An outline of the consequent production operation is described, based on vapour phase and laser processing. Continuous long-term reproducibility is achieved. Analysis of the product by glow discharge mass spectrometry with state-of-the-art sensitivity is used for qualification of the product and process. Results from this and supplementary techniques which have been used are presented. The utilisation of this material for GaAs has been widely tested successfully. The outcome of some of that work is shown. © 1990.