Correlation of vapor pressure equation and film properties with trimethylindium purity for the MOVPE grown III V compounds
The purity of trimethylindium (TMI) has improved significantly during the past few years, as a result of improvements in its synthesis and purification. However, consistent high purity and batch-to-batch variation remain as primary concerns. In the present study, the impurity concentrations in commercial TMI samples were analyzed at part per billion levels using Fourier transform-nuclear magnetic resonance spectroscopy, inductively coupled plasma-optical emission spectrometry, and inductively coupled plasma-mass spectrometry techniques. The impurity profiles of TMI were compared with the electrical characterization of grown InP layers, e.g. electron mobility, carrier concentration, and glow discharge mass spectrometry analyses of grown layers in order to establish a correlation. The vapor pressure equation for TMI was also re-evaluated using (a) dynamic concentration measurements by Epison™ monitor and (b) the direct measurement of vapor pressures at various temperatures using a solid-state Baratron™ capacitance manometer. The resultant equations are reported along with a novel delivery system (UNI-FLO™ cylinder) that provides consistent, reproducible delivery of TMI in the vapor phase. The influence of deleterious impurities on the optoelectronic properties is discussed along with the synthesis and purification strategies for the consistent manufacture of high-purity TMI.