Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films. Issue 20 (6th May 2022)

• Record Type: Journal Article
• Authors: Willis, Joe; Bravić, Ivona; Schnepf, Rekha R.; Heinselman, Karen N.; Monserrat, Bartomeu; Unold, Thomas; Zakutayev, Andriy; Scanlon, David O.; Crovetto, Andrea
• Is Part Of: Chemical science. Volume 13:Issue 20(2022)
• Page Start: 5872
• Page End: 5883
• Publication Date: 2022-05-06
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d2sc01538b
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : We synthesize air-stable, p-type CaCuP thin films with high hole concentration and high hole mobility as potential p-type transparent conductors. We study their optoelectronic properties in detail by advanced experimental and computational methods. Abstract : Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concentration and hole mobility exceed 1 × 10 20 cm −3 and 35 cm 2 V −1 s −1 at room temperature, respectively. Transport calculations indicate potential for even higher mobilities. Copper vacancies are identified as the main source of conductivity, displaying markedly different behaviour compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calculations of phonon-mediated indirect transitions. This discrepancy could be partly attributed to crystalline imperfections within the films, increasing the strength of indirect transitions. We determine the transparent conductor figure of merit of CaCuP films as a function of composition, revealing links between stoichiometry, crystalline quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.