Conductance modification of molybdenum oxide thin films through oxygen-vacancy engineering for visible-blind ultraviolet photodetection

We propose a simple approach to locally modify the conductance of molybdenum oxide thin films with thermal annealing in oxygen atmosphere at relatively low temperature for constructing a visible-blind ultraviolet photoconductor. The amorphous MoOx is grown by remote plasma enhanced atomic layer deposition (RPALD), and then crystallized into alpha-MoOx at 500 degrees C in argon atmosphere, which exhibits good conductance with resistivity of 3.9 x 10(-3) Omega cm due to the formation of oxygen vacancies. Good ohmic contact between Ti and the crystallized MoOx is demonstrated with specific contact resistance of 9.74 x 10(-4) Omega cm(2). The lateral Au/Ti-MoOx-Ti/Au structures are defined and the conductance of the exposed MoOx channel is significantly modified by thermal annealing in oxygen atmosphere to form a photodetector, which shows obvious photoresponse at the wavelength of less than 372 nm with low dark current of 0.9 pA at 5 V, and the remarkable responsivity of 0.75 mA W-1 at 280 nm is achieved with a high ultravoilet/visible rejection ratio. The low dark current and incredible responsivity can be attributed to the good ohmic contacts of untreated MoOx and the reduction of number of oxygen vacancies in the MoOx channel. The key role of oxygen vacancy on the conductance of MoOx has been demonstrated. Those results suggest that the MoOx thin films are promising candidate for visible-blind ultraviolet photodetectors in a simple complementary metal oxide semiconductor (CMOS)-compatible process.