Thermal stress control of the polymorphic transformation in MnTe semiconductor films

Abstract

The polymorphic transformation of the compound MnTe between its wurtzite-type (β) and nickeline-type (α) crystalline phase results in a significant change in its physical properties. In this study, the effect of thermal stress on the β→α transformation in MnTe films was investigated by varying the materials used for the MnTe film's capping layers (Ni, Ti, Mo, W, and SiO2). The capping layer/β-MnTe stacked films were heated above the transformation temperature, and the volume fraction of the material that transformed during the heating was evaluated using XRD measurements. In-plane compressive thermal stress observed at the interface between the MnTe film and capping layer promotes the β→α transformation. The in-plane thermal stress at the interface that induces the β→α transformation has linear temperature dependence, and the gradient of this dependence was estimated to be around −20.5 MPa K−1. The obtained results indicate that the polymorphic transformation of the MnTe film can be controlled by the thermal stress generated by mechanical constraints induced by the surrounding layers. The results of this study offer new insights into the design of MnTe-based phase-change devices and the application of straintronics in semiconductor films.