Random laser action in 3-D ZnO nanostructures

Room-temperature ultraviolet random lasing with low threshold pumping power was successfully achieved by ZnO 3-D random-wall nanostructure fabricated on ZnO/SiO₂/Si substrate through a thermal chemical reaction and vapor transportation deposition method in a simple horizontal tube furnace from the mixed ZnO and graphite powders. The nanorods grown along c-axis on the substrate are coalesced to form the 3-D nano-wall with 80~100 nm in wall thickness and irregular height ranging of 95-250 nm. Mueller matrix spectroscopic ellipsometry reveals that evaluated refractive indices n (E) of ZnO nanowalls are well interpreted by taking account of the ratio between ZnO and void achieved by effective medium theory analysis and isotropic depolarization feature of the designated nanowalls. Random lasing action observed in the wide wavelength range between 375 and 395 nm is realized by coherent amplification of the closed-loop scattered light inside 3-D random-wall nanostructure. It is demonstrated that both transverse electric (TE) and transverse magnetic (TM) modes show the same threshold and pumping power dependent trend, while the intensity of TM lasing is weaker than that of TE due to the different scattering strength originated from the features of the inside of nano wall.