Difficulty of carrier generation in orthorhombic PbO

Abstract

Polycrystalline β-PbO films were grown by pulsed laser deposition in atmospheres ranging from oxygen-poor (the oxygen pressure of 0.01 Pa) to oxygen-rich (13 Pa) conditions, and the oxygen chemical potential was further enhanced by ozone annealing to examine hole doping. It was found that each of the as-grown β-PbO films showed poor electrical conductivity, σ < 1.4 × 10−7 S cm−1, regardless of the oxygen pressure. The density functional calculations revealed that native defects including Pb and O vacancies have deep transition levels and extremely high formation enthalpies, which indicates difficulty of carrier generation in β-PbO and explains the experimentally observed poor electrical conductivity. The analysis of the electronic structures showed that the interaction between Pb 6s and O 2p orbitals is weak due to the deep energy level of Pb 6s and does not raise the valence band maximum (VBM) level unlike that observed in SnO, which is also supported by ultraviolet photoemission spectroscopy measurements. The deep acceptor transition levels of the native defects are attributed to the deep VBM of β-PbO. On the other hand, annealing β-PbO films in reactive oxygen-containing atmospheres (i.e., O3) led to a significantly enhanced electrical conductivity (i.e., σ > 7.1 × 102 S cm−1) but it is the result of the formation of an n-type PbO2 phase because oxygen chemical potential exceeded the phase boundary limit. The striking difference in carrier generation between PbO and SnO is discussed based on the electronic structures calculated by density functional theory.

Ab Initio Design of Pb2+-based Ternary Oxides for Phase Stable and Hole Dopable p-type Oxides

“…The defect calculation and hole dopability prediction is consistent with experimental reports that tetragonal phase PbO only shows n -type conduction . Monoxide PbO in a different polymorph, orthorhombic phase, is also intrinsically insulating . PbO forms a sharp contrast to SnO in which V O does not form spontaneously .…”

“…PbO forms a sharp contrast to SnO in which V O does not form spontaneously . Sn-5s orbital, by hybridizing with O-2p orbital at VBM in SnO, leads to a shallow VBE position and thus high p -type dopability. − …”

“…(iv) Experimentally oxides will assume the amorphous 37 Monoxide PbO in a different polymorph, orthorhombic phase, is also intrinsically insulating. 38 PbO forms a sharp contrast to SnO in which V O does not form spontaneously. 39 Sn-5s orbital, by hybridizing with O-2p orbital at VBM in SnO, leads to a shallow VBE position and thus high p-type dopability.…”

Achieving Narrowed Bandgaps and Blue‐Light Excitability in Zero‐Dimensional Hybrid Metal Halide Phosphors via Introducing Cation–Cation Bonding

“…An obvious strategy to raise the VBM is to use a cation that has high-lying occupied d 10 or s 2 orbitals, which can produce high-lying antibonding states with the occupied p orbitals of a given anion. [40][41][42][43][44] Thus, cations such as Sb 3+ and Cu + are often highly desired. On the other hand, low-lying unoccupied orbitals of a cation generally lead to a low-lying CBM, [45][46][47][48] and the formation of cationcation bonding states [49,50] can further lower the CBM.…”

Semiconducting Double-Layer Lead Monoxide Tin Oxide Nanostructures for Photodetectors

“…As a result, incorporating a PbO layer in the passive films is expected to decrease the Mott–Schottky slope while improving the dielectric constant. Despite the fact that the exact figures of lead-doped compounds are not known, PbO polymorphs’ optical and structural properties could be determined. − In photovoltaic applications, α-PbO offers potential uses thanks to its band gap ranging between 1.9 and 2.2 eV, , whereas β-PbO, which is the other form of it, can be utilized as surface modifiers. − The β-PbO phase offers a band gap of 2.7 eV. It is observed that β-PbO is stable at temperatures above 488 °C.…”