A narrow photoluminescence linewidth of 21 meV at 1.35 μm from strain-reduced InAs quantum dots covered by In0.2Ga0.8As grown on GaAs substrates

InAs quantum dots with size fluctuations of less than 4% were grown on GaAs using the self-assembling method. By covering the quantum dots with ${\mathrm{In}}_{\mathrm{0.2}}{\mathrm{Ga}}_{\mathrm{0.8}}\mathrm{As}$ or ${\mathrm{In}}_{\mathrm{0.2}}{\mathrm{Al}}_{\mathrm{0.8}}\mathrm{As},$ strain in InAs dots can be partly reduced due to relaxation of lattice constraint in the growth direction. This results in low-energy emission (about 1.3 μm) from the quantum dots. The photoluminescence linewidth can be reduced to 21 meV at room temperature. This width is completely comparable to the theoretical limit of a band-to-band emission from a quantum well at room temperature. Because the dots can be uniformly covered by the strain reducing layers, factors that degrade size uniformity during coverage, such as compositional mixing or segregation, will be suppressed, allowing for an almost ideal buried quantum dot structure.