MBE-grown Ni_yMg_1-yO and Zn_xMg_1-xO Thin Films for Deep Ultraviolet Optoelectronic Applications

Abstract

We report on the heteroepitaxial growth of high-quality single crystal cubic Zn x Mg 1-x O and Ni y Mg 1-y O thin films by radio frequency oxygen plasma-assisted molecular beam epitaxy (RF-MBE). Film compositions over the ranges x = 0 to x = 0.65 and y = 0 to y = 1 have been grown on lattice-matched MgO (100) and characterized optically, morphologically, compositionally, and electrically. Both of these ternary materials are shown to have bandgaps which vary directly as a function of transition metal (Ni or Zn) concentration. Optical transmission measurements of Ni y Mg 1-y O show the bandgap to shift continuously over the approximate range 3.5 eV (for NiO) to 4.81 eV (for y=0.075). Similarly, the bandgap of cubic Zn x Mg 1-x O is shifted from about 4.9 eV (for x = 0.65) to 6.25 eV (for x=0.12). Films exhibit good morphological quality and typical roughness of Ni y Mg 1-y O films is 5 Å while that of Zn x Mg 1-x O is less than 15 Å, as measured by atomic force microscopy (AFM). X-ray diffraction (XRD) is employed to confirm crystal orientation and to determine the films' lattice constants. Film compositions are interrogated by Rutherford Backscattering (RBS) and electrical characterization is made by room-temperature Hall measurements.