Uniform InAs quantum dots (QDs) have been realized on GaAs by molecular beam epitaxy, which can increase maximum optical gain in laser diodes without sacrificing original high-density and high optical quality characteristics. This improvement enables laser operation under higher environment temperature. In order to improve QD uniformity, we searched for a proper growth condition and sequence for suppressing In out-diffusion during QD coverage. Although the same initial InAs QD structure on GaAs was used, PL linewidth was reduced after coverage under such improved conditions. In QD lasers, higher optical gain as large as 54 cm(-1) at room temperature which is about 10 cm(-1) larger than our previous data was realized. Those improved QDs are attractive for realizing novel optical devices. (c) 2012 Elsevier B.V. All rights reserved.