Growth of high mobility GaN by ammonia-molecular beam epitaxy

The growth of high electron mobility GaN on (0001) sapphire by ammonia molecular beam epitaxy is reported. A buffer layer of AlN <300 Å is initially deposited by magnetron sputter epitaxy, a technique where the aluminum source is a planar dc magnetron sputter cathode and ammonia is used for the nitrogen source. The GaN epilayer is deposited using a conventional K cell for the gallium source and ammonia for the nitrogen source. The layers were doped using silane. Measured room temperature electron mobilities of 560 cm²/V s were observed for layers with carrier densities of ${\text{∼1.5×10}}^{17} {\mathrm{cm}}^{\mathrm{-3}}.$ The 4 K photoluminescence spectrum showed a very strong donor bound exciton at 3.48 eV with a full width at half maximum (FWHM) of 4.9 meV. X-ray diffraction studies showed the layers to have good crystallinity with FWHM of the ω–2θ and ω scans as low as 13.7 and 210 arcsec, respectively.