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.

GaN films were grown on sapphire by molecular beam epitaxy (MBE). Two sources of activated nitrogen were investigated: an electron cyclotron resonance (ECR) plasma, and hydrogen azide (HN3). With the ECR plasma source, typical growth rates were ∼ 0.1 μm/h. Films grown in this manner showed significant surface damage from ions, and little if any photoluminescence. With HN3, growth rates were ∼ 0.25 μm/h. Azide-grown films showed smooth surfaces, and sharp band-to-band photoluminescence. This is the first reported use of HN3 to grow III–V nitrides by MBE, and it shows great promise as a nitrogen source.


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