WSe(2-x)Tex alloys grown by molecular beam epitaxy

The growth of WSe(2-x)Tex alloys by molecular beam epitaxy has been demonstrated for the first time to investigate the phase transition from the semiconducting 2H phase to the semi-metallic 1T' phase as a function of Te concentration. Up to 14% Te incorporation, stable alloys in the semiconducting 2H phase are achieved while above 79% Te incorporation, stable alloys in the semi-metallic 1T' phase are obtained. Our results indicate the MBE-grown WSe(2-x)Tex alloys exhibit a miscibility gap from 14% to 79% Te concentrations at a growth temperature of 250 degrees C, a temperature compatible with direct vertical back-end-of-line integration. This miscibility gap results in phase separation of two different alloys, both with different composition and crystal structure. While the alloying of small Te concentrations does indeed result in a desired reduction of the semiconducting bandgap, the phase separation above 14% Te incorporation prohibits bandgap tuning for a wider range of applications. These results highlight the competing energies and kinetics associated with producing uniform WSe(2-x)Tex alloys.