Session:

Copper iodide (CuI) is a non-toxic earth-abundant wide bandgap semiconductor with many potential technological applications in transparent electronics. Transparent conducting p-type semiconductors CuI and CuAlO₂ have lower electrical conductivities compared to their doped n-type counterparts In₂O₃:Sn or ZnO:Al. CuI possesses the highest electrical conductivity of its class as a transparent p-type semiconductor (σ~10² Scm^-1) due to its high hole mobility (μ~10¹ cm²V^-1s^-1) and carrier concentration (p~10¹⁹ cm^-3) whilst boasting a large Seebeck coefficient (α~280 μVK^-1), mainly attributed to p-type doping with copper vacancies (V_Cu) ^[1,2]. Intrinsic doping via controlling deposition conditions and extrinsic doping with chalcogens allows for control over the crystal quality and carrier concentration ^[3,4,5,6,7]. Sulfur and selenium doping increases the CuI carrier concentration (p~10²⁰ cm^-3) ^[4,6]. Optimizing the intrinsic defect structures in undoped CuI is predicted to yield even higher electrical conductivity ^[8]. Ion implantation, a well-established microfabrication technique, can be used for defect engineering via noble gas implantation, known to also improve thermoelectric properties by reducing lattice conductivity and vacancy doping ^[9].
In this work, we elucidate the role of intrinsic point defects in low-energy noble gas ion implanted into ion beam sputtered CuI thin films. Ion energies 13, 27, and 70 keV were used to implant neon, argon, and xenon with fluences between 5×10¹⁴ ions cm^-2 and 1.92×10¹⁶ ions cm^-2. Microstructural, compositional, and electronic characterization showed stoichiometric γ-CuI. Moderate implantation fluences (≤2×10¹⁵ ions cm^-2) led to a 100% increase in carrier concentration (~1×10²⁰ cm^-3) without significant loss in Seebeck coefficient (~200 μVK^-1) or carrier mobility (~9 cm²V^-1s^-1). This led to the increase of the power factor by two-fold to α²σ~540 μWm^-1K^-2. Transport of Ions in Matter (TRIM) ^[10] simulations showed that the damage per atom (DPA) ranged between 1.2 and 16. Density functional theory (DFT) calculations showed that Frenkel pairs (low formation energy defect complexes) are likely produced through ion implantation. We will present detailed results discussing the relationship between point defect formation and thermoelectric performance of CuI thin films supported with Monte Carlo simulations and DFT calculations.
References:
[1] Yang, C. et al. (2017), Nature Communications 8(1), 16076. [2] Yang, C. et al. (2016), Proceedings of the National Academy of Sciences 113.46, 12929-12933. [3] Grauzinyte, M. et al. (2019), Physical Chemistry Chemical Physics, 21, 18839-18849. [4] Murmu, P. P. et al. (2022), ACS Applied Energy Materials, 3(10), 10037-10044. [5] Ahn, K. et al. (2022), Chemistry of Materials, 34(23), 10517-10527. [6] Storm, P. et al. (2021), Physica Status Solidi RRL, 15, 2100214. [7] Markwitz, M. et al. (2023), Surfaces and Interfaces, 41, 103190. [8] Willis, J. et al. (2023), Chemistry of Materials, 35(21), 8995-9006. [9] Burcea, R. et al. (2022), ACS Applied Energy Materials, 5(9), 11025-11033. [10] Ziegler, Z. F. et al. (2010), Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 268(11-12), 1818-1823.

Co-Author(s): Peter Murmu (GNS Science), Ben Ruck (Victoria University of Wellington), Takao Mori (National Institute for Materials Science (NIMS)), John Kennedy (GNS Science)

Martin Markwitz

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