Correlation of film properties and reduced impurity concentrations in sources for III/V-MOVPE using high-purity trimethylindium and tertiarybutylphosphine

Abstract

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.