TRIISOPROPYLINDIUM - DECOMPOSITION STUDY AND USE FOR LOW-TEMPERATURE GROWTH OF INAS

The organometallic vapor phase epitaxial (OMVPE) growth of In-containing III-V semiconductors typically uses trimethylindium (TMIn). However, TMIn suffers from several problems. First, it is well known that the effective vapor pressure of solid TMIn changes with time because of changes in the surface area. Secondly, TMIn decomposes slowly for temperatures lower than 400-degrees-C in an atmospheric pressure OMVPE reaCtor; it is too stable for some low-temperature applications. In addition, it causes carbon contamination, especially at low temperatures, due to the CH3 radicals. Thus, there is a need for new In precursors that are liquids at room temperature and do not contain CH3 radicals. This work reports the first decomposition and OMVPE growth studies for a newly developed indium source, triisopropylindium (TIPIn). The decomposition study was carried out in an isothermal flow tube reactor with the reaction products analyzed using a mass spectrometer. The temperature for 50% decomposition is approximately 110-degrees-C for TIPIn in a He ambient. This is about 200-degrees-C lower than that for TMIn under SiMilar conditions. The mass spectroscopic peaks occur at m / e = 39, 42, 43, 71, and 86. The relative intensities indicate that the major product for TIPIn decomposition is C6H14. This suggests that TIPIn decomposes by homolysis, producing C3H7 radicals that mainly recombine to produce C6H14. The OMVPE growth study was carried out in an atmospheric pressure OMVPE reactor in H-2 with AsH3 as the As source. InAs epilayers with good surface morphologies were obtained for temperatures as low as 300-degrees-C at a V/III ratio of 460. The necessary V/III ratio increases as the growth temperature is decreased, due to the incomplete decomposition of AsH3 at low temperatures. The less reactive C3H7 radicals from TIPIn pyrolysis produce far less carbon in the solid than the more reactive CH3 radicals produced by TMIn pyrolysis. A disadvantage of TIPIn is the low growth efficiency, due to parasitic reactions. Thus, it appears that TIPIn may be best suited for low pressure OMVPE or, particularly, for chemical beam epitaxy.