1 research outputs found
Recrystallization of Highly-Mismatched Be<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>O Alloys: Formation of a Degenerate Interface
We investigate the effect of thermally
induced phase transformations on a metastable oxide alloy film, a
multiphase Be<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>O (BZO), grown on Al<sub>2</sub>O<sub>3</sub>(0001)
substrate for annealing temperatures in the range of 600–950
°C. A pronounced structural transition is shown together with
strain relaxation and atomic redistribution in the annealed films.
Increasing annealing temperature initiates out-diffusion and segregation
of Be and subsequent nucleation of nanoparticles at the surface, corresponding
to a monotonic decrease in the lattice phonon energies and band gap
energy of the films. Infrared reflectance simulations identify a highly
conductive ZnO interface layer (thicknesses in the range of ≈10–29
nm for annealing temperatures ≥800 °C). The highly degenerate
interface layers with temperature-independent carrier concentration
and mobility significantly influence the electronic and optical properties
of the BZO films. A parallel conduction model is employed to determine
the carrier concentration and conductivity of the bulk and interface
regions. The density-of-states-averaged effective mass of the conduction
electrons for the interfaces is calculated to be in the range of 0.31<i>m</i><sub>0</sub> and 0.67<i>m</i><sub>0</sub>. A
conductivity as high as 1.4 × 10<sup>3</sup> S·cm<sup>–1</sup> is attained, corresponding to the carrier concentration <i>n</i><sub>Int</sub> = 2.16 × 10<sup>20</sup> cm<sup>–3</sup> at the interface layers, and comparable to the highest conductivities
achieved in highly doped ZnO. The origin of such a nanoscale degenerate
interface layer is attributed to the counter-diffusion of Be and Zn,
rendering a high accumulation of Zn interstitials and a giant reduction
of charge-compensating defects. These observations provide a broad
understanding of the thermodynamics and phase transformations in Be<sub><i>x</i></sub>Zn<sub>1–<i>x</i></sub>O
alloys for the application of highly conductive and transparent oxide-based
devices and fabrication of their alloy nanostructures