Quantum dot vertical-cavity surface-emitting lasers covering the ‘green gap’

Semiconductor vertical-cavity surface-emitting lasers (VCSELs) with wavelengths from 491.8 to 565.7 nm, covering most of the ‘green gap’, are demonstrated. For these lasers, the same quantum dot (QD) active region was used, whereas the wavelength was controlled by adjusting the cavity length, which is difficult for edge-emitting lasers. Compared with reports in the literature for green VCSELs, our lasers have set a few world records for the lowest threshold, longest wavelength and continuous-wave (CW) lasing at room temperature. The nanoscale QDs contribute dominantly to the low threshold. The emitting wavelength depends on the electron–photon interaction or the coupling between the active layer and the optical field, which is modulated by the cavity length. The green VCSELs exhibit a low-thermal resistance of 915 kW −1 , which benefits the CW lasing. Such VCSELs are important for small-size, low power consumption full-color displays and projectors. Semiconductor lasers: quantum dots plug the ‘green gap’ Researchers have used vertically oriented devices containing tiny quantum dots to improve the production of green laser light. While powerful red and blue lasers can be easily manufactured using multilayered semiconductors, finding material combinations that generate green wavelengths is trickier. Baoping Zhang from Xiamen University in China and co-workers cracked this problem by turning to vertical-cavity surface-emitting lasers (VCSELs) whose emission wavelength can be controlled by adjusting their cavity length. Fabricating a VCSEL with an active layer composed of indium–gallium–nitrogen quantum dots reduced the threshold currents needed to emit green light, thanks to the strong quantum confinement effects. The team demonstrated VCSELs with different wavelengths that covered the ‘green gap’ and used heat-dissipating materials to produce a continuous-wave device that operates at room temperature.