X-ray and Raman analyses of GaN produced by ultrahigh-rate magnetron sputter epitaxy

Thick films of GaN were studied by x-ray diffraction and Raman spectroscopy. The GaN thick films were deposited on (0001) sapphire using ultrahigh-rate magnetron sputter epitaxy with typical growth rates as high as 10-60 μm/min. The width of the x-ray rocking curve from the (0002) reflection for the sample produced by this technique is ∼300 arcsec, which is unprecedented for GaN produced by a sputtering-type process. Our recent sample shows an x-ray rocking curve width of 240 arcsec. Only allowed modes were observed in the polarized Raman spectra. The background free carrier concentration is lower than 3×10¹⁶cm^-3. The phonon lifetime of the Raman E₂⁽²⁾ mode of the sputtered GaN was comparable to that of bulk single crystal GaN grown by sublimation. The quality of the film was uniform across the wafer. The film was thermally stable upon annealing in N₂ ambient. The x-ray and Raman analyses revealed that the sputtered GaN films are of high crystalline quality.