Growth, optical properties and device characterisation of InAs/GaAs quantum dot bilayers

The growth and optical properties of InAs/GaAs quantum dot (QD) bilayers are investigated, where the strain interactions between closely spaced QD layers are exploited to tailor the optical properties of the system. The underlying (seed) layer acts as a template for subsequent growth of the upper layer, whose properties can then be modified due to the greater freedom in the choice of growth conditions. Extension of the emission wavelength of the QDs is observed, to 1400 nm at room temperature for GaAs-capped bilayers and extending to 1515 nm for InGaAs-capped bilayers. The QDs in the second layer are highly uniform, resulting in an inhomogeneous broadening of <20 meV and, for small separations between QD layers, efficient carrier tunnelling results in suppression of emission from the seed layer. Edge-emitting lasers incorporating QD bilayers operating either in the ground state or first excited state at 1340 nm at room temperature are demonstrated, showing comparable behaviour to QD lasers containing independent layers. Ground state lasing at 1425 nm at 250 K is also observed.