Properties of Excitons in Strain-engineered InAs/InGaAs/GaAs Metamorphic Quantum Dots for Long Wavelength (1.3 to 1.55 µm) Emission

Lasers with long wavelength emission (1.3 µm to 1.55 µm) are useful for telecommunications due to low attenuation in optical fibers. Although lasers based on self-assembled quantum dots (QDs) emitting at 1.3 µm are commercially available, producing longer wavelength devices has proven challenging. One possible route for achieving this is the use of strain-engineered InAs/InGaAs/GaAs quantum dots grown on metamorphic InGaAs layers, where InGaAs is used as upper and lower confining layers for exciton confinement. The desired wavelength emission is controlled by two independent parameters.1-2 (1) By changing the amount of indium in the upper confining layer (UCL) and lower confining layer (LCL). This changes the band discontinuities between the QDs and confining layers and also affects the mismatch and strain. (2) Thickness "d" of the LCL which affects only the mismatch between the QDs and LCL. By this method it should be possible to optimize the confinement whilst also extending the wavelength to 1.55 µm: emission as long as 1.59 µm in similar metamorphic nanostructures has been reported.3 Measuring the emission wavelength is straightforward, but how about the confinement? Here we do this by studying physics of exciton properties like (radius and reduced mass) using low temperature magneto-photoluminescence under varying magnetic field.4 We have characterized thirteen samples of strain-engineered InAs/InGaAs/GaAs QDs at 2 K and in magnetic field 0 - 15 T. Due to different In composition (0.09 to 0.31) and LCL thickness (19 nm to 1000 nm) in these samples, reduced masses of excitons are found to vary between 0.08 - 0.27 m0, while exciton radii vary from <10 nm to 23 nm.