Room-Temperature Stimulated Emission in ZnO: Doubts on Excitonic Lasing

Concerning stimulated emission, we discuss for ZnO the roles of excitonic processes and of recombination in an inverted electron-hole plasma. While excitonic processes are well justified at lower temperatures and densities, doubts arise concerning the concept of excitonic lasing in ZnO at or even above room temperature. The densities at laser threshold and at room temperature are frequently at or above the Mott density, but below the density at which population inversion is reached. We suggest alternative processes in a non-inverted plasma.