Nanowires containing quantum structures (dots or wires) offer direct integration of light emitters with ultra-small optical cavities. Applications include nanoscale lasers and single photon sources with high extraction efficiencies. These structures have high surface to volume ratios so surface passivation is a significant consideration, requiring a careful choice of materials.
We report the growth and structural and optical characterisation of GaAsP nanowires containing either GaAs quantum dots (QDs) or quantum wells (QWs). This novel common group-III system offers a number of advantages in comparison to previously studied systems, including deep confinement potentials, reduced surface recombination and lack of an absorbing core when fabricating laser structures. Structures are grown by molecular beam epitaxy (MBE) on Si substrates allowing potential direction integration with drive electronics. TEM studies reveal high quality, defect free structures but a complex GaAsP structure with regions having different P compositions, suggesting the formation of QD and quantum wire regions within the nanowire. Evidence for GaAsP related-QDs is seen in low temperature micro-PL spectra. Nanowires containing radial QWs exhibit highly efficient QW carrier capture and a large activation energy for temperature dependent PL, consistent with strong carrier confinement. A laser structure containing three radial GaAs QWs exhibits a very low pumping threshold at low temperatures. Initial studies of nanowires containing GaAs QDs show excellent structural and optical properties. Our results indicate the potential of the GaAs/GaAsP system for improved lasers and single photon sources.
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