For the growth of GaAs and AlGaAs by metalorganic chemical vapor deposition (MOCVD), the residual carrier concentration was confirmed to follow the relation of [Carrier concentration] proportional to [V/III](-4/3). As this relation fit various growth conditions, it provided a basis for a new parameter of "effective TBAs concentration" which represents the concentration of the tertiarybutylarsine (TBAs) effectively contributing to the growth of epitaxial layer. By using this new parameter, a large spatial variation of the efficiency of TBAs across a wafer in a direction of the gas flow was indicated for the growth of Ga(AI)As at low temperature of 500 degrees C. With using this parameter, the decomposition of 1,1-dimethylhydrazin (DMHy) was suggested to occur only on the wafer at this temperature. The optimized TBAs flow rate for the growth of GaInNAs deduced by considering the distribution of the effective TBAs concentration coincided with the optimized actual input TBAs flow rate. This coincidence supported the appropriateness of the method of measuring the efficiency of TBAs on the wafer with the effective TBAs concentration. The optimized TBAs flow rate obtained by using the new parameter was applied to the growth of a GaInNAs quantum well (QW) and to the fabrication of a high quality laser diode emitting at 1.21 mu m. (c) 2006 Published by Elsevier B.V.