Correlation of film properties and reduced impurity concentrations in sources for III/V-MOVPE using high-purity trimethylindium and tertiarybutylphosphine
Trimethylindium (TMI) and tertiarybutylphosphine (TBP) are an attractive combination of sources for Metalorganic vapor phase epitaxy (MOVPE) of InP-based compounds. TBP is used to deposit high-quality layers at significantly lower V/III ratios, and is less hazardous than phosphine. Although source purities have improved considerably, consistent quality remains a concern. In the present work, metallic and organic impurities in the sources were measured at ppb levels, using analytical techniques such as FT-NMR, GC-MS, and ICP-OES. Impurity profiles were compared with the electrical properties of InP grown by using TMI and TBP at 600 °C and V/III ratio of 20. The films show 77 and 300 K Hall mobilities of 140,000 and 4850 cm 2/Vs respectively, and a background carrier concentration of 1.5×10 14 cm -3. For comparative evaluation, InP films were grown using TMI and PH 3 under optimized conditions at 580-600 °C and V/III ratio of 450-800 to achieve 77 and 300 K Hall mobilities as high as 287,000 and 5400 cm 2/Vs, and a background carrier concentration about 6-8×10 13 cm -3. The impact of deleterious impurities on electronic properties is discussed along with the "oxygen-free" synthetic strategies to metalorganic sources such as TMI, TBP and TBAs. Also reported are the results achieved with a novel delivery system (Uni-Flo™ cylinder) that has greatly improved the evaporation of solid sources such as TMI, Cp 2Mg and CBr 4 providing stable vapor concentration and greater than 95% utilization of precursors during MOVPE growth.