The University of Texas at El Paso
Metallurgical and Materials Engineering
Faculty Sponsor's Department(s):
Characterization via Atom Probe Tomography of CdXZn(1-X)Te Growth on Micro- Patterned CdS Substrates
Cadmium telluride is the most desired material system for thin film solar cells since it holds the lowest inherent manufacturing cost. However, there are many key aspects of the material that are still not well understood. The difference between the theoretical and laboratory CdTe photovoltaic efficiencies are attributed to the high defect densities due to large lattice mismatch between the CdS and CdTe films and the non-uniformity of grains in the layers. One way to reduce the defect densities in CdTe solar cells is to add a ZnTe buffer layer between CdTe and CdS. Furthermore, implementing micro and nano enabled pseudomorphic selective growth of CdxZn(1-x)Te will increase the energy conversion efficiency of CdTe modules by increasing the open circuit voltage. In this work, we report the uniform selective-area growth of CdTe/ZnTe islands on micro patterned-SiO2/CdS/ITO/glass wafers using a novel physical vapor deposition technique known as close-spaced sublimation. The ZnTe and CdTe are deposited selectively on the CdS and not the SiO2 due to a much greater surface diffusion length on the SiO2. The ZnTe was deposited first, followed by the CdTe. Uniform growth selectivity was observed using scanning electron microscopy. The X- ray diffraction analysis from the micro islands demonstrated continuous intermixing between ZnTe and CdTe, resulting in a graded CdxZn(1-x)Te. Additionally, atom probe tomography will be used to confirm compositional grading at the atomic scale. The aforementioned findings will show promise in understanding the role of defects on lattice mismatched heterostructures.