A process for is provided for synthesizing a compound having the formula E(GeH.sub.3).sub.3 wherein E is selected from the group consisting of arsenic (As), antimony (Sb) and phosphorus (P). GeH.sub.3Br and [CH.sub.3).sub.3Si].sub.3E are combined under conditions whereby E(GeH.sub.3).sub.3 is obtained. The E(GeH.sub.3).sub.3 is purified by trap-to-trap fractionation. Yields from about 70% to about 76% can be obtained. The E(GeH.sub.3).sub.3 can be used as a gaseous precursor for doping a region of a semiconductor material comprising Ge, SnGe, SiGe and SiGeSn in a chemical vapor deposition reaction chamber.