Phys. Rev. Lett. 108, 157402 (2012)

Lasing in ZnO nanowires at room temperature does not rely on excitons, as previously thought, but is instead likely due to an electron–hole plasma. That's the finding of Marijn Versteegh and co-workers from Utrecht University in The Netherlands, who have analysed the situation using a many-body quantum theory. Excitons — electron–hole pairs bound by the Coulomb force — are known to play an essential role in ZnO lasing at cryogenic temperatures, and it was widely thought that they would continue to be important at higher temperatures due to their large binding energy of 60 meV. However, it now seems that this is not the case. In previous work, the researchers developed a many-body quantum theory for describing the optical properties of a high-density interacting electron–hole gas in ZnO. When they applied this theory to the case of lasing, their theory accurately predicted the observed laser threshold, photon energy of the laser emission and peak spacing in the laser spectra.