Electron backscatter diffraction of CdTe thin films: Effects of CdCl2 treatment

Abstract

In this work, the authors describe procedures to prepare the surface of close-spaced sublimation CdTe thin films necessary for producing good electron backscatter diffraction (EBSD) data. They found that polishing resulted in an amorphous layer on the surface and no Kikuchi pattern; however, ion-beam milling produced a relatively flat and good-quality surface, resulting in high-quality patterns and, consequently, excellent EBSD data. The authors used a combination of polishing and ion-beam milling or etching to study the crystalline structure of the CdTe film at different depths. They also used EBSD, in conjunction with other analytical techniques, to investigate the effects of the CdCl2 treatment, performed at different temperatures and times, on the recrystallization process of physical vapor deposition CdTe thin films. The authors found that the untreated films were ⟨111⟩ oriented, with grain sizes smaller than 1μm. The CdCl2 at 350 °C produced partially recrystallized films, whereas treatments at 400 °C or 420 °C produced completely recrystallized films, with no texture, and grains with grain sizes varying from about 1μm to more than 40μm. These films were so flat that good EBSD data could be obtained without any surface preparation. Atomic force microscopy and scanning electron microscopy showed that large grains had different morphologies than smaller grains, and EBSD showed that these large grains had ⟨111⟩ texture. These results indicate that the (111) surface is the lowest energy surface in these films and, consequently, ⟨111⟩-oriented grains grow at the expense of grains oriented in less-favorable directions. Regardless of the deposition method and treatment, the CdTe films have a high density of 60° ⟨111⟩ twin boundaries.