Nitrogen doping of cuprous oxide films: A surface science perspective

[Display omitted] •Preparation of high quality pristine and nitrogen-doped Cu2O films on Au(111) and Pt(111).•Thorough surface-science analysis of the doped films by XPS, STM, LEED and PL spectroscopy.•Measuring the thermal stability of the N-dopants in the Cu2O matrix.•Identifying O substitutional sites as primary binding positions of the N-atoms.•Determining the nitrogen desorption temperature to 500 K, too low for practical applications. Nitrogen doping of Cu2O films grown on Au(111) and Pt(111) supports was explored by a variety of surface-science techniques, including electron-diffraction, X-ray photoelectron-spectroscopy (XPS), scanning tunneling microscopy and photoluminescence spectroscopy (PL). The films were prepared by Cu vapor deposition and high-pressure oxidation at 50 mbar O2. Nitrogen was inserted by adding N2 to the reactive gas or via sputter doping. Only the latter resulted in a clear N1s signal in XPS, compatible with the insertion of N-atoms at O substitutional sites. The N-doping caused an overall degradation of the oxide lattice and suppressed the formation of the (√3×√3)R30° surface reconstruction observed on pristine Cu2O(111). Moreover, the oxide Fermi level shifted from the valence-band top into the band gap, indicative for a reduced p-type conductivity of the sample upon doping. The N-dopants featured low thermal stability and largely desorbed at around 500 K, leaving behind a pronounced 850 nm PL peak due to O vacancy emission. Our findings indicate that the N-atoms initially occupy O substitutional sites but get removed easily at moderate temperature, casting doubts whether N-doping is a suitable pathway to improve the conductance and luminescence behavior of Cu2O.