Hole doping in VO$_{2}$ thin films

Chemical doping has been used to modulate the metal-semiconductor transition in VO$_{2}$ extensively. Here, we investigated the effect of aliovalent Al$^{3+}$ doping in VO$_{2}$ thin films on the Metal-Semiconductor Transition (MST) in comparison with the effect of isovalent Mn$^{4+}$ doping. Raman spectroscopy and x-ray diffractometry were used to confirm the monoclinic phase and estimate the lattice strain caused by the doping. The concentration and the valence state of the dopants observed by XPS will be discussed. The Al$^{3+}$ ions are expected to introduce holes into the conduction band of the VO$_{2}$, and the evidence for hole doping by Al$^{3+}$ was observed by Hall effect measurements. This effect has not been reported previously. Both types of dopants were found to increase the change of the resistivity across the MST, and they also shifted the T$_{\mathrm{MST}}$.