Transformation from MoO3 into MoS2: Experimental study on phase transition and energy band modulation

Abstract

The transformation of MoO3 into MoS2 is investigated by sulfurizing MoO3 on sapphire at various temperatures. The amorphous MoO3 are crystallized at 500 ℃ and then sulfurized from 500 ℃ to 900 ℃. The phase transition occurs as the temperature increases, from MoO3 to S- doped MoO3 at 500 ℃, mixture of MoO3 and MoS2 at 600 ℃, O- doped MoS2 at 700 ℃, ideal stoichiometric ratio of MoS2 at 800 ℃, and S- deficient MoS2 at 900 ℃, respectively. Correspondingly, the work function is significantly modulated from 4.68 eV for MoO3 to 3.90 eV for MoS2, and the band gap energy decreases from 3.08 eV to 1.00 eV gradually, which are fairly consistent with the theoretical predictions. The contacts between titanium and S- doped MoO3, or the mixture of MoO3 and MoS2, are ohmic- like contacts with specific contact resistivities of 2.68 × 10-3 Ω•cm2 and 3.14 × 10-3 Ω•cm2. While the contacts between Ti and O- doped MoS2, ideal stoichiometric ratio of MoS2, or S- deficient MoS2 are Schottky contacts with barrier heights of 0.22 eV, 0.43 eV and 0.45 eV, respectively. Those results demonstrate that temperature plays pivotal role in determining the phase of sulfurized MoO3 and their properties.