Aluminum (Al) hydrocarbon precursor compositions are provided that can be used for vapor deposition of transition metal carbide thin films, for example aluminum-doped transition metal carbide thin films such as Al-doped titanium carbide thin films. In some embodiments, the precursor compositions comprise one or more isomers of tritertbutyl aluminum (TTBA). In some embodiments the precursor compositions comprise at least 50% of Isomer 1 of TTBA, at least 50% of Isomer 2 of TTBA, or at least 20% of a combination of Isomer 1 and Isomer 2, where Isomer 1 has the formula Al(tert-Bu)2(iso-Bu) and Isomer 2 has the formula Al(tert-Bu)(iso-Bu)2. A container containing a precursor composition comprising at least 50% of Isomer 1 or Isomer 2 or at least 20% of a combination of Isomer 1 and 2 of TTBA can be attached to a vapor deposition reactor and used to deposit transition metal carbide thin films such as Al-doped titanium carbide thin films by atomic layer deposition or chemical vapor deposition.