Structural and optical properties of 2H phase WSe2

2H-WSe2 films were synthesized by magnetron co-sputtering of tungsten and selenium targets onto SiO2/Si(100), SiO2/Si(111), and Al2O3(0001) substrates in an Ar atmosphere at 150 °C, without any additional vacuum selenization step. After rapid thermal annealing at 700 °C in Ar, x-ray diffraction confirmed the formation of the optimal crystal phase. Films grown on SiO2/Si exhibited lower strain compared to those deposited on Al2O3. We demonstrated that (002)-textured WSe2 films with a thickness of approximately 50 nm can be achieved, and that planar-like growth is maintained for films thinner than about 60 nm. Raman spectroscopy showed the characteristic E2g and A1g modes of 2H-phase WSe2 at 248 cm−1 and 251 cm−1, corresponding to in-plane and out-of-plane vibrational phonon modes, respectively. The indirect optical bandgap of few-layer WSe2 was determined to be between 1.43 eV and 1.49 eV, with the bandgap varying as a function of film thickness—an expected property of 2D materials such as WSe2.