Polarity determination of ZnO thin films by electron holography

Abstract

The polarity of the ZnO film grown on sapphire using an ultrathin Ga wetting layer has been investigated by electron holography. Spontaneous polarization of the ZnO film leads to localized charges in the surface, which change the potential distribution in the vacuum side of the film. The potential distribution depends on the nature of the bounded charges and change as a function of the distance from the film surface. By studying the dependence of the potential change on the distance from the film surface, the ZnO film with very thin Ga wetting layer is determined to have the [0001] polarity.

Cubic nitridation layers on sapphire substrate and their role in polarity selection of ZnO films

“…The same procedures were used to determine the polarity of Sample B, which turns out to be O polar. 12 The results are confirmed by convergent beam electron diffraction method ͑not shown here͒, and are also consistent with our in situ observations of reflection high energy electron diffraction: the 4 ϫ 4 and 3 ϫ 3 surface reconstructions 13,14 were observed from Samples A and B, respectively.…”

“…The film polarity was determined by using the EH method proposed by Xu et al 12 Figure 1 shows the results: Figs. 1͑a͒-1͑c͒ for Sample A, and Figs.…”

“…1͑c͒, one can clearly see that phase change in the vacuum region decreases with increasing distance from the edge of the sample. Based on the method by Xu et al, 12 Sample A has a Zn polarity. The same procedures were used to determine the polarity of Sample B, which turns out to be O polar.…”

Confinement effects in ultrathin ZnO polymorph films: Electronic and optical properties

“…Bulk gap widths and densities of states (DOS) have been scrutinized by first principles simulations 10,11 and we have recently disentangled the effects of band narrowing and of electrostatics in the modifications of quasi particle, absorption and electron energy loss spectra 12 . Beyond bulk properties, the possibility of tuning electronic and optical properties through a reduction of dimensionality has fostered advances in the fabrication and structural characterization of ZnO nanostructures [13][14][15][16][17][18][19] and thin films on various substrates [20][21][22][23][24][25][26][27][28][29][30] , with a range of techniques and under a variety of experimental conditions. In particular in ultra-thin films, theoretical and experimental works indicate important variations of the atomic structure as a function of thickness [31][32][33][34] .…”

Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions

“…If there is no external electric field, the above equation can be simplified as follows: 16,17 ⌬ ͑x,y͒ = C E V 0 t͑x,y͒, ͑2͒…”