X-RAY CHARACTERIZATION OF GAN ALGAN MULTIPLE-QUANTUM WELLS FOR ULTRAVIOLET-LASER DIODES/

GaN/Al0.20Ga0.80N (50 Angstrom/50 Angstrom) multiple quantum wells (MQ W) with 15 periods were grown on (0001) sapphire substrates by molecul ar beam epitaxy and evaluated by x-ray diffraction. To simulate an ult raviolet laser diode structure, the substrate was coated first with n- GaN as the bottom contact layer and n-Al0.25Ga0.75N as the correspondi ng cladding layer. The crystal structure of this system was investigat ed by studying the reciprocal lattice map of off-axis diffraction peak s as well as the theta-2 theta pattern around the (0002) reflection. T he MQW was found to be coherent and has the a-lattice parameter of the underlying Al0.25Ga0.75N. The good agreement between experimental and theoretical data in the relative intensity of up to third-order satel lite peaks supports that the interfaces of the MQW are abrupt, and thu s, interdiffusion of Ga and Al atoms at the growth temperature was neg ligible. (C) 1998 American Institute of Physics.