Structural characterization of a-plane Zn1-xCdxO (0≤x≤0.085) thin films grown by metal-organic vapor phase epitaxy -: art. no. 023514

Zn1-xCdxO(11 (2) over bar0) films have been grown on (01 (1) over bar2) sapphire (r-plane) substrates by metal-organic vapor phase epitaxy. A 800-nm-thick ZnO buffer, deposited prior to the alloy growth, helps to prevent the formation of pure CdO. A maximum uniform Cd incorporation of 8.5 at. % has been determined by Rutherford backscattering spectrometry. Higher Cd contents lead to the coexistence of Zn1-xCdxO alloys of different compositions within the same film. The near band-edge photoluminescence emission shifts gradually to lower energies as Cd is incorporated and reaches 2.93 eV for the highest Cd concentration (8.5 at. %). The lattice deformation, due to Cd incorporation, has been described using a new reference frame in which the lattice distortions are directly related to the a-plane surface structure. Cd introduction does not affect the c lattice parameter but expands the lattice along the two perpendicular directions, [11 (2) over bar0] and [1 (1) over bar 00], resulting in a quadratic volume increase. (c) 2006 American Institute of Physics.