All-Inorganic, Bicontinuous, Bandgap-Engineered Epitaxially-Fused PbSe Quantum Dot/CdS Matrix Heterostructures for Optoelectronic and Electronic Applications

We report all-inorganic, bicontinuous, bandgap-engineered epitaxially fused PbSe QD/CdS matrix heterostructures achieved through postdeposition sequential colloidal atomic layer deposition (c-ALD). The CdS matrix grows epitaxially on the PbSe QDs to ultimately fully infill the interstitial space between fused PbSe QD arrays in an interpenetrating fashion, resulting in bicontinuous semiconductor heterostructures. The low-energy excitonic absorbance of the epitaxially fused PbSe QD assembly is maintained, and the absorbance at energies above the CdS matrix bandgap increases. The c-ALD grown CdS matrix enhances the oxidative and thermal stability of the QD assemblies, allowing us to preserve the QD/matrix heterostructure upon annealing at 150 °C. By controlling the number of c-ALD cycles and by thermal annealing, we tailor stoichiometry and modulate carrier type, concentration, and mobility probed in the platform of field-effect transistors and the dark current density and responsivity of infrared-absorbing PbSe QD/CdS matrix heterostructure photoconductors. Photoconductors treated with c-ALD and annealed showed an increase in photocurrent modulation, enhancing infrared photoresponsivity. The bicontinuous, bandgap-engineered semiconductor QD/matrix heterostructures provide an architecture that promises the high mobility charge transport and long carrier lifetimes needed to achieve high speed and high quantum efficiency electronic and optoelectronic devices.