Strain dependence of lasing mechanisms in ZnO epilayers

The lasing characteristics of highly disordered ZnO thin films deposited on Si O 2 ∕ Si substrates with and without a MgO buffer layer have been investigated. We observed that the emission spectra of the ZnO epilayers with and without a MgO buffer are associated with the radiative recombination of free-exciton ( ∼ 380 nm ) and electron-hole plasma ( ∼ 395 nm ) , respectively. The difference in the lasing wavelength is due to the induced compressive (tensile) strain along the c axis of the ZnO epilayers as a result of the presence (absence) of the MgO buffer layer. It is demonstrated that the strain-induced variation of Mott density inside the ZnO epilayers is responsible for the observed lasing characteristics.