Abstract
We report the observation of single quantum dot (QD) emission in the telecoms C-band (1530–1565 nm) from an InAs QD structure grown on a Si substrate. A large red-shift of the emission is achieved by capping InAs QDs with a thin GaAsSb layer. Sharp lines, representing emission from single QDs, are observed out to wavelengths as long as 1540 nm. Comparison is made to the optical properties of a nominally identical active region structure grown on a GaAs substrate. Single QD emission from a Si-based system at 1500 nm has the potential for single photon sources compatible with current optical fibers and reduced complexity of integration with drive electronics.
Highlights
The unique, discrete electronic density of states exhibited by semiconductor quantum dots (QDs) provides many applications for both conventional and novel light emitters
A third mechanism contributing to the extension of the emission wavelength is a transition to a type-II system for Sb compositions above ∼14%,6,8,13,17,23 with the hole localized in the GaAsSb two-dimensional layer and the electron in the QD
Related to the structures studied in the present work are GaSb QDs and quantum rings grown in a GaAs matrix.[24−31] These form a type-II system but with the electrons localized in the GaAs and holes in the QD or ring.[25,29]
Summary
Article to a nominally identical reference sample grown on a GaAs substrate. The present results suggest the potential for Si-based single photon sources emitting in the C-band. Thickness fluctuations result in a broadening of the emission, with further broadening due to alloy fluctuations.[47] It is difficult to estimate the size of this broadening; the TEM image of Figure 1a shows a highly nonuniform GaAsSb layer thickness and X-STM studies of similar samples reveal a nonuniform Sb composition.[11,22] A structural study of InAs QDs capped with a GaAs0.78Sb0.22 layer shows significant alloy fluctuations (∼12%) with Sb-rich clusters of lateral dimensions between 10 and 20 nm.[22] For relatively large composition and/or layer thickness fluctuations, the GaAsSb layer will break up into a series of quasi-QDs48 with full spatial localization of the hole In this case, spectral broadening is still possible via the population of different hole states during the many recombination processes that occur within the integration time required to acquire the PL spectra.
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