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InAs self-assembled quantum dots (QDs) embedded within an InGaAs quantum well have been grown on InP substrate by low-pressure metalorganic vapor phase epitaxy. We find out that the underlying InGaAs layer could affect the dot growth dramatically in terms of size distribution and luminescence efficiency. After inserting a thin GaAs interface layer between the underlying InGaAs and the InAs QD layer, improved dot size uniformity and strong room temperature photoluminescence (PL) up to 2 μm were observed. In the case of InAs QDs with no GaAs layer, one has to reduce InAs QD layer thickness in order to obtain room temperature PL. These results suggest that InAs from the underlying InGaAs layer contribute to the InAs QD formation, and cause the InAs QDs to be non-uniform, but a thin GaAs interface layer could effectively block the migration of In atoms from the InGaAs layer toward InAs QDs, and therefore lead to more uniform QD formation with better luminescence efficiency. [Copyright &y& Elsevier]