Visible lasing from GaN:Eu optical cavities on sapphire substrates

We report visible (red) lasing emission from Eu-doped GaN thin films grown on sapphire substrates. The edge emission fulfills the requirements of stimulated emission properties: super-linear characteristic, spectrum line narrowing, polarization effect, lifetime reduction, and longitudinal modes in a Fabry–Perot cavity. The GaN:Eu active layer has low threshold (∼10 kW/cm2) for the onset of lasing. The optical gain and loss are of the order of 50 and 20 cm−1, respectively. Growth conditions are investigated for gain enhancement and loss reduction. To obtain the high gain and low loss active layer, N-rich growth conditions are required. Channel waveguide cavities result in 5× increase in gain value compared to planar waveguides.