Effect of Ag, Cu, and Co Underlayers on Luminescence and Lasing of Vapor-Phase-Grown ZnO Microcrystals

In this paper, the preliminary study of room-temperature photoluminescence (PL) of ZnO microcrystals grown from vapor phase on sapphire substrates with thermal deposited thin layers of Ag, Cu, and Co (Ag/ZnO, Cu/ZnO, Co/ZnO) is presented. Ag/ZnO and Cu/ZnO samples consisted of vertically oriented "labyrinths" and microrods, respectively. Co/ZnO crystals were shaped like rods but with no preferred orientation. PL spectra of all studied samples included only UV emission; visible emission was absent. The PL intensity of ZnO crystals grown on metals was increased as compared to ZnO grown on bare substrates, which was attributed mainly to surface morphology enhancement. Random lasing was observed in Ag/ZnO and Cu/ZnO PL spectra. Lasing excitation in Ag/ZnO was relatively easy; lasing threshold in this case was 7 times lower than that in Cu/ZnO (0.2 vs. 1.4 MW/cm
²
).