Tailoring optical and resistance properties of the functional CuAlxOy semiconductor for applications as thermal infrared imagers

This is the first report on the optical and resistance properties of copper aluminum oxide thin films for applications as thermal infrared imagers. The deposition of these films was investigated under three series of reactive magnetron sputtering conditions. Structural characterization identified the P63mmc hexagonal crystalline structure of CuAlO2 although the 150- to 350-nm thick films were in a non-stoichiometric CuAlxOy ratio. The thermal coefficient of resistance of the CuAlxOy films was measured to be in the range 1.7–2.2%/K and the resistivity ranged from 0.3 to 1.0 Ω cm with n-type nature. To explain the low indirect bandgap value of the CuAlxOy films, a type-I band alignment bulk heterojunction between CuAlO2 and Cu2O is proposed. This provides an effective method to decrease the resistivity and increase the thermal coefficient of resistance. From their optical characterization, a refractive index of 2.27 ± 0.07 was deduced, thus favoring the CuAlxOy films for antireflection coating in the long infrared wavelength region. A micromachining process of CuAlxOy micro-bridges was demonstrated with well-defined shapes at a pixel pitch of 25 μm. These findings pave the way for the future development of high-performance thermal infrared imagers.