Optical and electrical properties of Al-WS₂ films via H₂S sulfurization of Al-WO_x

We have studied the composition, structure, optical and electrical properties of the Al-WS₂ (un-doped and Al-doped WS₂) films deposited by radio frequency (RF) magnetron sputtering and post-sulfuration processing. Results of Raman spectra show that Al-WS₂ films have two predominant peaks at ~350cm^-1 and ~420cm^-1, assigned to E_2g¹ and A_1g of pure WS₂. Meanwhile, the intensity of the Raman peak (at ~252cm^-1) corresponding to Al₂S₃ increases with adding the Al doping contents. As for optical properties, absorption excitonic peaks at ~1.94 and ~2.35eV are comparable to those of WS₂ single crystals. The optical band gaps of the Al-WS₂ films can be tuned by different Al doping contents. Hall measurements were performed to study the electrical properties. Hall mobility of un-doped WS₂ films is 1.40×10¹cm²V^-1s^-1, and that of the Al-WS₂ films decreases to 1.16cm²V^-1s^-1 with Al content increasing to 3.66%. The comparable Hall mobility of Al-WS₂ films can be obtained by controlling appropriate Al doping contents. Furthermore, WS₂ films undergo transitions from n-type conductivity to p-type conductivity when the films are doped with Al.