Nanotech 2010

Theoretical Studies in Epitaxial Stabilization of ZnO-based Light-emitting Semiconductors

P-L Liu, Y-J Siao, M-H Lee
National Chung Hsing University, TW

Keywords: light emitting diode, first-principle simulation, epitaxial softening


The device quality ZnO films are expected to next generation materials applied in the field of photo-electronic devices. We find that (0001)-oriented ZnO, Zn0.875Be0.125O, Zn0.875Mg0.125O, and Zn0.875Al0.125O strained layer lattices soften as lattice parameter of the epilayer is compressed and these strained layer lattices become stiffer upon dilation (tensile strain). Our findings also indicate that the ZnO strained layers could be stabilized with increasing the aluminium concentrations, which Al is at substitutional sites in the underlying Zn lattice. Furthermore, we are going to analyze the epitaxial softening of (0001)-, (10-10)-, and (2-1-10)-oriented ZnO strained layer superlattices for providing further insight into the stress/strain distributions in and around coherently strained ZnO-based systems. We find that the elastically softest direction is <2-1-10> and the hardest direction is <0001>. The results of our calculations are consistent with reported experimental observations that <2-1-10>-oriented ZnO is more stable than (0001)- or (10-10)-oriented ZnO. In addition, the harmonic behavior of the Zn1-x(Be,Mg,Al,Cd)xO indicated that the harm( [11-23]) is the lowest. Our result is consistent with the experimental observations that the (11-23) faces of three-dimensional ZnO pyramids grow faster than (0001) and (10-10) faces.
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