InAs quantum dots (QDs) were grown on InP substrates by low pressure-metalorganic chemical vapor deposition. Disilane (Si2H6 was used as an n-type dopant. The positions of Si doping were varied: buffer layer, capping layer, modulation doping, and QD itself. Surface treatment of InP by Si2H6 was also performed to see the effect of Si on InAs QD. Photoluminescence (PL) and atomic force microscopy (AFM) were used to characterize optical and structural properties of QDs, respectively. It was found that the PL peak positions varied from 0.73 to 0.88 eV with the position of Si doping. PL peak blue shift in modulation doped sample was explained in terms of state filling effect. It was found that Si doping at QD itself was the most effective way to obtain the strongest integrated PL intensity without degrading the QD size distribution. (C) 2003 Published by Elsevier B.V.