Band alignment and electrical characterizations of a grafted Si/MgCdTe <i>p–i–n</i> heterojunction

Abstract

Thin-film solar cells offer high power density and efficiency, making them attractive for terrestrial and space applications. Among these, cadmium telluride (CdTe) is a leading material due to its direct bandgap and high absorption coefficient. However, further improvements in efficiency and open-circuit voltage (Voc) are hindered by intrinsic p-type doping limitations, limiting the built-in potential (Vbi) and the corresponding Voc. To address this, we utilize semiconductor grafting to integrate a single-crystal p-type silicon nanomembrane onto an epitaxial MgCdTe layer, forming a Si/MgCdTe heterojunction while overcoming lattice mismatch constraints. Using x-ray photoelectron spectroscopy, we determine a type-I band alignment with conduction and valence band offsets of 0.66 and 0.45 eV, respectively. Additionally, we fabricate a p–i–n heterojunction diode, demonstrating a satisfying rectification ratio and a moderate ideality factor. This work provides a possible pathway for high-efficiency CdTe-based photovoltaics and Si/MgCdTe tandem cells, leveraging precise band alignment engineering and high p-type doping to enhance Voc in single junction cells and higher-efficiency multijunction cells.