Recrystallization of Highly-Mismatched BexZn1鈥?i>xO Alloys: Formation of a Degenerate Interface

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• 作者：Dae-Sung Park ; Sepehr K. Vasheghani Farahani ; Marc Walker ; James J. Mudd ; Haiyuan Wang ; Aleksander Krupski ; Einar B. Thorsteinsson ; Djelloul Seghier ; Chel-Jong Choi ; Chang-Ju Youn ; Chris F. McConville
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2014
• 出版时间：November 12, 2014
• 年：2014
• 卷：6
• 期：21
• 页码：18758-18768
• 全文大小：608K
• ISSN：1944-8252

文摘

We investigate the effect of thermally induced phase transformations on a metastable oxide alloy film, a multiphase Be_xZn_1鈥?i>xO (BZO), grown on Al₂O₃(0001) substrate for annealing temperatures in the range of 600鈥?50 掳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 鈮?0鈥?9 nm for annealing temperatures 鈮?00 掳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 0.31m₀ and 0.67m₀. A conductivity as high as 1.4 脳 10³ S路cm^鈥? is attained, corresponding to the carrier concentration n_Int = 2.16 脳 10²⁰ cm^鈥? 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_xZn_1鈥?i>xO alloys for the application of highly conductive and transparent oxide-based devices and fabrication of their alloy nanostructures.

Keywords:

phase transformation; oxide alloys; BeZnO; degenerate interface; atomic diffusion; defect engineering