AlGaInAs quantum dots were grown on GaAs (100) substrate with low-pressure metalorganic vapor phase epitaxy. Growth temperature and trimethylaluminum input was varied to investigate their effects on quantum dot density and size. A model was proposed, the results agreed well with experiment. The morphological characteristics were interpreted in terms of adatom migration and nucleus stability, as well as pyrolysis of input precursors. The optimal growth temperature and aluminum composition in the vapor phase were estimated in order to achieve high quantum dot density. Under optimal growth conditions, quantum dot density can be as high as 2 x 10(10) cm(-2), about 1.5 times of aluminum-free quantum dots grown at the same temperature. (C) 2004 Elsevier B.V. All rights reserved.