OPTICAL CHARACTERISTICS OF P-TYPE GAN FILMS GROWN BY PLASMA-ASSISTED MOLECULAR-BEAM EPITAXY

Using a molecular beam epitaxy system equipped with an inductively cou pled radio frequency nitrogen plasma source, p-type GaN films were gro wn on sapphire substrates with no postgrowth treatment. Uniformity of the surface morphology and spatial homogeneity of the luminescence of the films were investigated using scanning electron microscopy and cat hodoluminescence (CL) imaging, respectively. By examining the dependen ce of photoluminescence on the excitation laser power density at 6 and 300 K, three different emissions having different origins were identi fied. A blue emission at similar to 3.25 eV is associated with shallow Mg impurities, while two different lower-energy emissions at similar to 2.43 and similar to 2.87 eV are associated with deep Mg complexes. The spatial distributions of the shallow and deep Mg impurities domina ting the optical properties of the p-type GaN films were also examined along the growth direction by low- and room-temperature CL using an e lectron beam with a range of penetration depths. (C) 1996 American Ins titute of Physics.