Is Cu_3–xP a Semiconductor, a Metal, or a Semimetal?

Abstract

Despite the recent surge in interest in Cu3–x P for catalysis, batteries, and plasmonics, the electronic nature of Cu3–x P remains unclear. Some studies have shown evidence of semiconducting behavior, whereas others have argued that Cu3–x P is a metallic compound. Here, we attempt to resolve this dilemma on the basis of combinatorial thin-film experiments, electronic structure calculations, and semiclassical Boltzmann transport theory. We find strong evidence that stoichiometric, defect-free Cu3P is an intrinsic semimetal, i.e., a material with a small overlap between the valence and the conduction band. On the other hand, experimentally realizable Cu3–x P films are always p-type semimetals natively doped by copper vacancies regardless of x. It is not implausible that Cu3–x P samples with very small characteristic sizes (such as small nanoparticles) are semiconductors due to quantum confinement effects that result in the opening of a band gap. We observe high hole mobilities (276 cm2/(V s)) in Cu3–x P films at low temperatures, pointing to low ionized impurity scattering rates in spite of a high doping density. We report an optical effect equivalent to the Burstein–Moss shift, and we assign an infrared absorption peak to bulk interband transitions rather than to a surface plasmon resonance. From a materials processing perspective, this study demonstrates the suitability of reactive sputter deposition for detailed high-throughput studies of emerging metal phosphides.

Redox Chemistries for Vacancy Modulation in Plasmonic Copper Phosphide Nanocrystals

“…Both ranges of values are in close agreement with carrier densities determined from Hall measurements on bulk Cu 3−x P films (N h = 3.8 × 10 21 cm −3 ). 60 Solid-state NMR spectroscopy has recently been demonstrated as a sensitive technique for probing delocalized carriers in degenerately doped semiconductor nanocrystals. 25,61 For example, solid-state 77 Se NMR of Cu 2−x Se nanocrystals showed a downfield Knight shift with increased copper vacancies.…”

“…This analysis yields a narrower range of carrier densities (Table , N h Drude = 3.0–4.8 × 10 21 cm –3 ). Both ranges of values are in close agreement with carrier densities determined from Hall measurements on bulk Cu 3– x P films ( N h = 3.8 × 10 21 cm –3 ) …”

A Conductive 2D Conjugated Tetrathia[8]circulene‐Based Nickel Metal–Organic Framework for Energy Storage

“…It could be ascribed to quantum confinement effects, that is, Ni‐TTC with very small characteristic size (such as small nanoparticles) is a semiconductor. [ 16 ]…”

Size and Emission Control of Wurtzite InP Nanocrystals Synthesized from Cu3–xP by Cation Exchange

“…42−44 The NC concentration, C NC , was estimated from the absorption intensity of the final NC solution (see SI Section 2.1 and Figure S7 for details). The absorption coefficient of bulk Cu 3−x P was recently reported, 45 and taking into account the local field effect due to the small size, the calculated value for Cu 3−x P NC absorption coefficient at a wavelength of 400 nm is μ = 3.3 × 10 5 cm −1 . Using this coefficient, the final NC concentration (C NC ) for the samples in Figure 2a−d is plotted as a function of T f in Figure 2e (red curve).…”