Spatial Bandgap Engineered Nanowires: Synthesis And Optical Characterization

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. This work reported two novel thermal evaporation approaches for realizing spatial bandgap engineering in single alloy nanowires.In the first part, we proposed a source-moving growth approach in Vapor-Liqiud-Solid (VLS) route for growing bandgap gradient CdSSe nanowires. The synthesized CdSSe nanowires have a diameter ranging from 100 to 1000 nm and typical length up to 500μm. Along the length of as-grown nanowires, the composition can be continuously tuned from CdS at one end to CdSe at the other end, resulting in corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). Transmission Electron Microscopy (TEM) images show that the wire has high crystalline quality with the lattice spacing gradient along the length.In the second part of this work, we further proposed a substrate-moving approach for growing broad bandgap graded ZnCdSSe nanowires with an approximate diameter of 100 nm and typical length up to 30μm. The lattice spacing of these nanowires is also graded along the length, and the photoluminescence wavelengths of these nanowires are spanning the entire visible range. Besides, the photometric property of these nanowires can be controlled by the blue-, green- and red-color emission lengths. More particularly, under carefully selected growth conditions, on-nanowire white light emission has been achieved.With broad bandgap gradient in single nanowire, these bandgap engineered nanowires demonstrated here will have promising applications in broad band light absorption and emission devices, such as multicolor display and lighting, high-efficiency solar cells and detectors.