Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors

Abstract

The paucity of high performance transparent p-type semiconductors has been a stumbling block for the electronics industry for decades, effectively hindering the route to efficient transparent devices based on p–n junctions. Cu-based oxides and subsequently Cu-based oxychalcogenides have been heavily studied as affordable, earth-abundant p-type transparent semiconductors, where the mixing of the Cu 3d states with the chalcogenide 2p states at the top of the valence band encourages increased valence band dispersion. In this article, we extend this mixing concept further, by utilizing quantum chemistry techniques to investigate ternary copper phosphides as potential high mobility p-type materials. We use hybrid density functional theory to examine a family of phosphides, namely, MCuP (M = Mg, Ca, Sr, Ba) which all possess extremely disperse valence band maxima, comparable to the dispersion of excellent industry standard n-type transparent conducting oxides. As a proof of concept, we synthesized and characterized powders of CaCuP, showing that they display high levels of p-type conductivity, without any external acceptor dopant. Lastly, we discuss the role of Cu-coordination in promoting valence band dispersion and provide design principles for producing degenerate p-type materials.

Self‐Compensation in Transparent Conducting F‐Doped SnO2

“…The hybrid functional PBE0 developed by Adamo and Barone was used in order to combat the self‐interaction error and thus allowed for an accurate description of the band gap of SnO 2 . Hybrid functionals were consistently shown to provide improved calculations of both geometry and electronic structure, and PBE0 was shown to predict these properties for tin‐based TCOs with a high degree of accuracy . PBE0 incorporates 25% of exact Fock exchange to the PBE (Perdew, Burke, and Ernzerhoff) formalism.…”

Transparent Electrodes for Efficient Optoelectronics

“…This approach was recently supported experimentally with pellets of CaCuP (with weak absorption at 2.2 eV and stronger absorption at 2.7 eV), showing conductivities up to 500 S cm −1 , although thin films of this material have yet to be synthesized. [87] Figure 1 compares the conductivity of various high-performing transparent n-type and p-type conductors as a function of the synthesis temperature. It can be noted that at high values of conductivity the non-oxides tend to be more strongly absorbing due to their lower band gaps.…”

Deep vs shallow nature of oxygen vacancies and consequentn-type carrier concentrations in transparent conducting oxides

“…Next is ZnO, then In 2 O 3 , but all three are relatively large, meaning that the VBM will be deep. Consequently, electron carriers will be stable, in contrast to hole carriers, which explains the observed difficulty in p-type doping these systems [149][150][151].…”