Trimethylaluminium (Me3Al or TMA) and trimethylindium (Me3In or TMI) are the key precursors in the fabrication by MOVPE of higher brightness LEDs. VCSELs and solar cells and they must be oxygen free to achieve optimum results. An improved proton nuclear magnetic resonance spectroscopy technique (NMR) has been developed to allow the detection of impurity species Lit ppm levels. MOVPE growth tests of material thus characterised have been performed and a correlation of SIMS and PL data for layers to NMR indicated Purity is presented. A strong relationship was observed between oxygen levels in precursors and deposited layer structures. The best quality EpiPure(TM) TMA precursor. with non-detectable 0 levels. yielded <3 x 10(16) cm(-3) oxygen by SIMS in AlAs layers. Furthermore, Al0.8Ga0.2As and (Al0.8Ga0.2)(0.5)In0.5P layers deposited in a second reactor using a number of TMA and TMI samples and historical data confirmed this trend and low oxygen levels ( <2 x 10(17) cm(-3)) were obtained for high-purity EpiPure(TM) Sources. (C) 2002 Elsevier Science B.V. All rights reserved.