Geometries, vibrational frequencies and thermodynamic properties of trimeric rings [XMYH](3) and tetrameric clusters [XMYH](4), X=H,F,Cl,Br,l; M=Al,Ga,In; Y=N,P,As have been obtained at B3LY-P/LAN-L2DZP level of theory. Thermodynamic analysis of the oligomerization reactions shows that formation of cluster species in the gas phase is thermodynamically favorable in case of X=H. Furthermore, gas-phase generation of hexamer species [HMYH](6) should also be viable. Nitrogen-containing oligomers are highly stable in respect to dissociation, which makes them promising candidates for the stoichiometry controlled CVD of doped nitrides.