Nondestructive Monitoring of Defect Evolution in Epitaxial CdTe Thin Layers Grown on Si(111)

Abstract

Reduction of crystalline defect density and size is a major issue in optimization of thin film for industrial scale applications. It is particularly hard to achieve defect minimization due to the lack of statistically relevant techniques where defectinduced strain information is also available. In this work, we use a combination of highresolution transmission electron microscopy and synchrotron X-ray diffraction to investigate the evolution of defects during the growth of highly mismatched cadmium telluride (CdTe) films on silicon(111) as a function of growth temperature and layer thickness. High-resolution transmission electron microscopy was employed to show that the grown layers are epitaxial, following the [111] substrate orientation, and to identify the main defect type (double twins). Detailed reciprocal space maps obtained by synchrotron X-ray diffraction were used to identify the presence of additional intensities near the ( 113) and ( 002) CdTe bulk reciprocal space positions caused by these defects. Analysis of these maps allowed to retrieve the strain of the atoms inside defects as well as to evaluate their average size and density. We show that defect density decreases as a function of temperature but increases as a function of layer thickness, while defect size and the elastic energy of the atoms inside each defect increases up to 400 °C.

Stability and electronic structure of the low-Σgrain boundaries in CdTe: a density functional study

“…Figure 1 shows the atomic structure of Σ3 GBs, including (111) and two different (112) GBs. These structures have been verified experimentally [23][24][25][26]. In the Σ3 (111) GB, which can be considered a stacking fault between the zinc-blende and wurtzite structures, there is no DB and wrong bond, and the maximum deviation of Cd-Te bond length from the ideal value of 2.78 Å is less than 0.01 Å.…”

“…The determination of the atomic structure of the GBs often requires combined efforts of high-resolution microscopy with atomistic theoretical simulation. Recently, there have been a series of studies on GBs in CdTe [23][24][25][26], which is one of the most promising thin-film solar cell absorbers. Most of the theoretical studies have been limited to the symmetric tilt Σ3 GBs, (111) and (112), whose atomic structures were clearly identified by experiments [23][24][25][26].…”

“…Recently, there have been a series of studies on GBs in CdTe [23][24][25][26], which is one of the most promising thin-film solar cell absorbers. Most of the theoretical studies have been limited to the symmetric tilt Σ3 GBs, (111) and (112), whose atomic structures were clearly identified by experiments [23][24][25][26]. Because the symmetric tilt Σ3 GBs were experimentally observed in CdTe, it has been assumed that such a low-Σ-value GB has lower formation energy than other GBs with higher Σ values.…”

Retrieving the configuration of grain boundary structure in polycrystalline materials by extraordinary X-ray reflection analysis

“…Such extraordinary peaks, when detected, were maximized by scanning the sample azimuthal angle. Computational analysis of the retrieved X-ray results was carried out using a custom-written MATLAB script for the kinematical model (Als-Nielsen & McMorrow, 2011;Nordlund, 2002;Nordlund et al, 2005;Oliveira et al, 2014), described in the following section.…”

“…Two Mg crystals with 30 Â 30 Â 30 unit cells are simulated, with atomic positions following the bulk structure. The edges of these crystals are removed, making a sphere of atoms without any specific faceting in order to reduce form factor effects on the simulation (Nordlund, 2002;Oliveira et al, 2014). One of the crystals is left in a pre-defined orientation, while the other is rotated with respect to fixed axes that pass through the directions ½110, [010] and [001].…”