Sub-300 nm optically pumped ultraviolet lasers were realized on low-defect-density (0001) AlN substrates fabricated from single crystalline AlN boules. The AlxGa1–xN/AlyGa1–yN hetero-structures were grown by metal-organic vapor phase epitaxy near atmospheric pressure. The high structural quality of the pseudomorphically deposited films was confirmed by X-ray reciprocal space mappings and time-resolved photoluminescence (PL) studies of the multiple quantum well emission.
The initial PL-decay times for a sample emitting at 267 nm were 0.87 ns and 1.14 ns for T = 295 K and T = 14 K, respectively. Laser resonators with a length of about 1 mm were formed by cleaving the AlN crystal to obtain m-plane mirror facets. Lasing was demonstrated for various wavelengths between 267 and 291 nm with the threshold power density as low as 126 kW/cm2 for the shortest attempted wavelength. The laser emission was TE polarized for all emission wavelengths. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)