Multicolour Laser From A Single Bandgap-graded CdSSe Alloy Nanoribbon

Owning to its compact structure, high optical gain and stable output with high intensity, semiconductor nanowires have caught increasing attention. As one type of semiconductor nanowire, the semiconductor bandgap graded alloy nanowire (BGAN) has some special photoluminescence (PL), gain and absorption properties, due to its varying chemical components with its graded bandgap in different sections of the BGAN, which are essentially distinctive from those homogeneous semiconductor nanowires. These profound performances enable BGAN a promising optical material for realizing wide-spectrum tunable laser with small volume and compact structure.The optical gain bandwidth of a typical homogeneous semiconductor nanowire is about20nm in wavelength, therefore this property limits the tunability of the semiconductor nanowire, and makes it difficult for the application as wide-spectrum laser. Via a source-moving VLS growth approach, the CdSSe BGANs are synthesized with PL range from510nm to710nm for each nanowire. In principle, it provides an optical gain bandwidth of200nm in wavelength. However, when it comes to BGAN structure, the short wavelength light propagating along the BGAN encounters strong absorption, and as a consequence, the wide-spectrum laser is troublesome.By employing BGANs with some geometrical defects, the photon localization is realized in the one dimensional semiconductor nanostructure. As a result of the multiple-scattering induced by those defects, the localized optical cavities are formed in the nanoribbon. Consequently, the reabsorption problem is overcome. We also propose that multiple-scattering in BGAN is in week scattering region, and it is the waveguide effect that enhances multiple-scattering and establishes coherent feedback in nanoribbon. Nevertheless, dislike random laser, the laser behavior is non-chaotic in nanoribbon system. In this work, we elucidate a multicolour laser from a single nanoribbon, with a tuning range of61run, corresponding to a colour variation from red to yellow, and finally to green. By moving the excitation spot along the nanoribbon, the wavelength of laser could be tuned. Moreover, the simultaneous emitting laser in different colours is realized from the same nanoribbon.