Chemically Programmed Ultrahigh Density Two-Dimensional Semiconductor Superlattice Array

摘要

A superlattice is a periodic array of interactive quantum wells formednby materials with different band gaps.1 The diverse functionality arisesnfrom the energy gap variations at the interface that control the carriernflow, leading to numerous devices with many potential applications.2nThe conventional superlattice-fabrication strategies based on vaporliquid-nsolid growth (VLS) or molecular beam epitaxy (MBE)ntechniques are limited by their application limit, while a direct syntheticnroute could provide an alternative means of creating high-densitynsuperlattices. However, designing an ultrahigh density linear superlatticenarray consisting of periodic blocks of different-band-gapnsemiconductors in the strong confinement regime via a direct syntheticnroute remains an unachieved challenge in nanotechnology. Partial ionnexchange demonstrates such capabilities in producing metal-semiconductornsuperlattice structures,3 though this method is deficient innproducing a large area of alternating blocks with enhanced repeatndensity, as required for ultrahigh density junction-based applications.nHere we report a general synthesis route for the formulation of a largeareanultrahigh density superlattice array that involves adjoining multiplenunits of higher-band-gap ZnS rods by lower-band-gap prolate CdSnparticles at the tips. A single one-dimensional (1D) wire is 300-500nnm long and consists of periodic quantum wells with barrier widthsnof 5 nm provided by the 1.2 nm wide ZnS rods and well widths ofn1-2 nm provided by the CdS particles, defining the superlatticenstructure. The superlattice wires are self-assembled into twodimensionaln(2D) supercrystalline arrays over an area of 2.5 μm2 withnan ultrahigh pitch density of 3.5 nm between adjacent nanowires. Thensynthesis route allows tailoring of ultranarrow laserlike emissionsn(fwhm≈125 meV) originating from strong interwell energy dispersionnalong with control of the width, pitch, and registry of the superlatticenassembly. Such an exceptional high-density superlattice array is ofnfundamental scientific importance because of its physical scale belownthe de Broglie wavelength and could form the basis of ultrahigh densitynmemories in addition to offering opportunities for technologicalnadvancement in conventional heterojunction-based device applications.