Atomic Layer Deposition of Photoconductive Cu₂O Thin Films

Abstract

Herein, we report an atomic layer deposition (ALD) process for Cu 2 O thin films using copper(II) acetate [Cu(OAc) 2 ] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu 2 O thin films at temperatures of 180–220 °C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc) 2 to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu 2 O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approximately 20 nm thick Cu 2 O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu 2 O crystals.

Rapid Vapor-Phase Deposition of High-Mobility p-Type Buffer Layers on Perovskite Photovoltaics for Efficient Semitransparent Devices

“…Furthermore, we found the films to remain phase-pure Cu 2 O after storage in ambient air for 4 days (Figure S3). This is consistent with results other groups have reported on ALD Cu 2 O, in which no structural or compositional degradation occurred after storage in air . X-ray photoemission spectroscopy (XPS) measurements confirm the films to contain Cu in the 1+ oxidation state, with no 2+ satellites observed on the surface (Figure S4).…”

“…These semi-transparent devices are used as top-cells in four-terminal tandems with two types of silicon bottom cells that are industrially-relevant: p-type passivated emitter rear contact (PERC) and n-type silicon cells with polycrystalline silicon passivation. 39,40 We chose to focus on CuO x rather than NiO x because Cu 2 O can be grown at temperatures below 200 °C by chemical vapor deposition (CVD) or atomic layer deposition (ALD), 41 which are soft growth methods, unlike sputtering. We grew the CuO x layers by atmospheric pressure chemical vapor deposition (AP-CVD).…”

“…We chose to focus on CuO x rather than NiO x because Cu 2 O can be grown at temperatures below 200 °C by chemical vapor deposition (CVD) or atomic layer deposition (ALD), which are soft growth methods, unlike sputtering. We grew the CuO x layers by atmospheric-pressure chemical vapor deposition (AP-CVD).…”

“…The phase stability of Cu 2 O is narrow, and careful control of the processing conditions is required to avoid impurity phases such as Cu metal or CuO. , Although CuO is more thermodynamically stable at atmospheric pressure, phase-pure Cu 2 O can still be reproducibly achieved if the deposition temperatures are low (<320 °C), when reaction kinetics play a sizable role. , X-ray diffraction measurements showed the films (50 nm thick) to be phase-pure cubic Cu 2 O, with no crystalline CuO phase impurities detected (Figure S2). Furthermore, we found the films to remain phase-pure Cu 2 O after storage in ambient air for 4 days (Figure S3).…”

Solar-Blind UV Photodetector Based on Atomic Layer-Deposited Cu2O and Nanomembrane β-Ga2O3 pn Oxide Heterojunction

“…13 Although many studies of the ALD growth of metallic Cu have been reported, only a few studies related to ALD grown Cu 2 O have been performed. 14−16 As determined from their bandgaps, binary compound semiconductors including GaN, SiC, and ZnO are suitable for developing visible-blind UV detectors, which are required for higher responsivity in the UV range compared to lower energy ranges. To meet the criteria of a solar-blind photodetector with a cutoff wavelength below 280 nm, alloy engineering is used to tune the bandgap as high as 4.42 eV to eliminate the longer wavelength.…”