Comparative study of the interface passivation properties of LiF and Al2O3 using silicon MIS capacitor

• Published in: Applied physics letters 2024-04, Vol.124 (14)
• Main Authors: Parion, Jonathan, Scaffidi, Romain, Duerinckx, Filip, Sivaramakrishnan Radhakrishnan, Hariharsudan, Flandre, Denis, Poortmans, Jef, Vermang, Bart
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Comparative studies; Defects; Interfacial properties; Lithium; Lithium fluoride; MIS (semiconductors); P-n junctions; Passivity; Photovoltaic cells; Silicon; Solar cells
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0203484

Lithium fluoride (LiF) is currently a very popular dielectric material used as a passivation or transport layer in a variety of applications, especially in high-efficiency solar cells. Despite this, its conduction properties and interface behavior with silicon remain largely unexplored. In this work, a LiF metal–insulator–semiconductor (MIS) structure is fabricated and characterized, and its properties are compared to the well-understood aluminum oxide (Al2O3) MIS structure. First, a higher current density in LiF compared to Al2O3 is highlighted, as well as its PN junction-like behavior with n-type silicon (n-Si), being rather unconventional for a dielectric layer. C–V measurements showcase the likely presence of an interface defect, causing an increase in the apparent doping and a shift in the flatband voltage VFB by +70 meV. This defect is found to be of the acceptor type, which renders the interface fixed charge more negative and improves the field-effect passivation in the case of a negative Qf. Finally, a density of interface states D i t ≈ 2 × 10 11   cm − 2   eV − 1 was found for LiF/n-Si, which is a low value showing appropriate chemical passivation at the interface. Overall, this work enables us to shed more light on the interface properties of LiF on n-Si, which is an essential step toward its wider use in state-of-the-art solar cells and other silicon-based devices.