The effect of annealing on the structure of CdTe films electro-deposited on metallic substrates

Abstract

In this work we report the influence of post-deposition heat treatments on the structure of the CdTe films electro-deposited on stainless steel substrates. The CdTe films were annealed in air at various temperatures and time in order to investigate the influence of post-deposition heat treatments on the film structure. The various structural parameters, such as grain size, lattice constant and stress, were investigated using XRD. The results showed that the stress, grain growth and the re-crystallization of CdTe depends on the post-deposition annealing time and temperatures. In the initial stages of annealing when the grains grow in size, the grain growth process obeys a parabolic growth law. The re-crystallization process during annealing has two stages, in the beginning, the re-crystallization is dominated by random orientation of the grains followed by a second process in which once again the crystallites tend to orient in a particular direction. The value of activation energy for 20% re-crystallization in CdTe was estimated as 1.17±0.1 eV. The as-deposited film is under compressive stress and with annealing the compressive stress increases. For longer annealing times the stress changes from compressive to tensile. The calculated stress is ∼10 9 dyn/cm 2. Lattice parameter of the as-deposited film is larger than the powder sample and upon annealing lattice value increase and reaches a maximum and on further annealing for a long time it decreases and attains a value less than that of the powder sample. The calculated value of the change in band gap due to the stress, induced during the annealing, is in the range −13 meV⩽Δ E g⩽17 meV.