Indium Trichloride, Indium (III) Chloride, or InCl3 goes by many names and has many uses, but this material’s main use is to create an indium precursor for CVD (chemical vapor deposition). TMI (tri-methyl indium) is a precursor for indium deposition, much like TMG for gallium deposition. Both MOCVD precursors are discussed here: http://www.indium.com/compounds/led-mocvd-precursors/#application
So here is the flow of indium in LED manufacture:
In + Cl --> indium (III) chloride --> TMI --> LED
Chemical vapor deposition is only one way to deposit layers of indium on a surface though. Physical vapor deposition, such as sputtering and evaporation, are common. Here is my take on how chemical and physical deposition processes compare: http://documents.indium.com/qdynamo/download.php?docid=1957