Gallium nitride and its alloys promise to be key materials for future heterojunction semiconductor devices aimed at high frequency, high power electronic applications. However, manufacturing for such high performance products is challenged by reproducibility and material quality constraints that are notably higher than those required for optoelectronic applications. To meet this challenge, in situ mass spectrometry was implemented in AlGaN/GaN/AlN metalorganic chemical vapor deposition processes as a real-time process and wafer state metrology tool. In particular, the various pregrowth gas phase impurity levels within the reactor, measured by mass spectrometry in real time, were correlated to photoluminescence band-edge and deep-level properties measured postprocess. Band-edge intensities increased and deep-level intensities decreased with lower oxygen-containing impurity levels in the pregrowth environment. These real-time indications of oxygen impurity incorporation were used for fault detection and to optimize preprocess reactor conditioning involving degassing of the wafer susceptor and furnace liner elements. Because this in situ sensing provides a control on contaminants to assure high material quality and a fault detection capability as well, it is now implemented routinely for both purposes. These real-time contamination control and fault detection strategies complement an overall advanced process control program for GaN-based semiconductor manufacturing, offering a systematic methodology to improve the product quality of GaN-based electronic devices. (c) 2005 American Vacuum Society.