An Auger electron spectroscopy, x-ray photoelectron spectroscopy, secondary ion mass spectrometry and bulk analysis of pyrolytic boron nitride crucibles after vacuum baking

Abstract

The growth of high quality GaAs and AlGaAs using the molecular beam epitaxy (MBE) technique requires that all of the components of the system be kept very clean, especially the source materials (Ga, As, and Al), the crucibles, and the furnaces since they are at high temperatures during the growth of the material. The crucibles, made of pyrolytic boron nitride (PBN), are used after a cleaning procedure that consists of a 1 h heat treatment at 1600 °C in a vacuum of approximately 5×10−9 Torr or better. While this cleaning procedure has been used extensively, there have been no reported studies of the effectiveness of this procedure or its effect on the crucible. We have used mass spectrometry, AES, SIMS, XPS, and a modification of the LECO technique to study both baked and unbaked crucibles. In this paper we demonstrate that the cleaning procedure does remove impurities from the crucible, especially carbon. We also demonstrate that the cleaning procedure does not decompose the surface of the crucible as is commonly believed and that the recently observed dark striations on the interior of some of the crucibles after the bakeout are due to a physical restructuring of the surface and a possible local segregation of boron and not due to surface segregation of impurities such as carbon. We also present the first report of e-beam induced decomposition of boron nitride.