Spatial composition grading of quaternary ZnCdSSe alloy nanowires with tunable light emission between 350 and 710 nm on a single substrate

We demonstrated a general methodology of growing spatially composition-controlled alloys by combining spatial source reagent gradient with a temperature gradient. Using this dual gradient method, we achieved for the first time a continuous spatial composition grading of single-crystal quaternary Zn_xCd_1-xS_ySe_1-y alloy nanowires over the complete band gap range along the length of a substrate. The band gap grading spans between 3.55 eV (ZnS) and 1.75 eV (CdSe) on a single substrate, with the corresponding light emission over the entire visible spectrum. We also showed that the dual gradient method can be extended to achieve alloy composition control in two spatial dimensions. The unique material platform achieved will open a wide range of applications from color engineered display and lighting, full spectrum solar cells, multispectral detectors, or spectrometer on-a-chip to superbroadly tunable nanolasers. The growth methodology can be extended more generally to other alloy systems.