Monolithic semiconductor lasers capable of emitting over the full visible-colour spectrum have a wide range of important applications, such as solid-state lighting, full-colour displays, visible colour communications and multi-colour fluorescence sensing. The ultimate form of such a light source would be a monolithic white laser. However, realizing such a device has been challenging because of intrinsic difficulties in achieving epitaxial growth of the mismatched materials required for different colour emission. Here, we demonstrate a monolithic multi-segment semiconductor nanosheet based on a quaternary alloy of ZnCdSSe that simultaneously lases in the red, green and blue. This is made possible by a novel nanomaterial growth strategy that enables separate control of the composition, morphology and therefore bandgaps of the segments. Our nanolaser can be dynamically tuned to emit over the full visible-colour range, covering 70% more perceptible colours than the most commonly used illuminants.

Abstract:The ability of a single monolithic semiconductor structure to emit or lase in a broad spectrum range is of great importance for many applications such as solid state lighting and multi-spectrum detection. But spectral range of a laser or light emitting diode made of a given semiconductor is typically limited by its emission or gain bandwidth. Due to lattice mismatch, it is typically difficult to grow thin film or bulk materials with very different bandgaps in a monolithic fashion. But nanomaterials such as nanowires, nanobelts, nanosheets provide a unique opportunity. Here we report our experimental results demonstrating simultaneous lasing in two visible colors at 526 nm and 624 nm from a single CdSSe heterostructure nanosheet at room temperature. The 97 nm wavelength separation of the two colors is significantly larger than the gain bandwidth of a typical single II-VI semiconductor material. Such lasing and light emission in a wide spectrum range from a single monolithic structure will have important applications mentioned above.

Alloying of CdS and PbS could potentially provide an important semiconductor with a wide range of bandgaps, with bandedge emission from mid-infrared to visible green, for various optoelectronic applications. We investigate the possibility of CdPbS alloy formation in nanowire and nanobelt forms, especially the dependence of alloy composition on two different cooling routes. Our results show that rapid cooling immediately after the growth phase can lead to a high-quality uniform alloy with Cd composition larger than possible at thermal equilibrium and by natural cooling. On the contrary, unassisted natural cooling leads to the formation of axial or core-shell heterostructures, containing segments with pure CdS and CdPbS alloys with lower Cd content than through rapid cooling. Such heterostructures with green and mid-infrared emission provide simultaneous access to two widely separated wavelengths from a single monolithic structure and can be important for many applications. Our results can help identify strategies for growing nanostructures with uniform alloy of high Cd incorporation, core-shell structures with shell serving as a passivating or protecting layer, or interesting longitudinal heterostructures. Both various heterostructures and uniform alloys of these materials could be important for high-efficiency solar cells, novel detectors, and nanolasing in wide spectral ranges.

Erbium-containing materials of long lifetime and high Er density are important for achieving strong luminescence and high optical gain in compact integrated photonics devices. We have systematically studied the lifetime and crystal quality as a function of growth conditions for an erbium compound that we recently reported, erbium chloride silicate (ECS). The lifetime for the best quality ECS nanowires can be as long as 540 μs, the longest for high-density Er-materials, representing a lifetime-density product as high as 8.7 × 1018 s cm−3. Such high density, long lifetime erbium materials can find many interesting applications such as compact lasers or amplifiers.

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