Atomic Layer Deposition of PbS Thin Films at Low Temperatures

Abstract

Atomic layer deposition (ALD) is a viable method for depositing functional, passivating, and encapsulating layers on top of halide perovskites. Studies in that area have only focused on metal oxides, despite a great number of materials that can be made with ALD. This work demonstrates that, in addition to oxides, other ALD processes can be compatible with the perovskites. We describe two new ALD processes for lead sulfide. These processes operate at low deposition temperatures (45–155 °C) that have been inaccessible to previous ALD PbS processes. Our processes rely on volatile and reactive lead precursors Pb­(dbda) (dbda = rac-N 2,N 3-di-tert-butylbutane-2,3-diamide) and Pb­(btsa)2 (btsa = bis­(trimethylsilyl)­amide) as well as H2S. These precursors produce high quality PbS thin films that are uniform, crystalline, and pure. The films exhibit p-type conductivity and good mobilities of 10–70 cm2 V–1 s–1. Low deposition temperatures enable direct ALD of PbS onto a halide perovskite CH3NH3PbI3 (MAPI) without its decomposition. The stability of MAPI in ambient air is greatly improved by capping with ALD PbS. More generally, these new processes offer valuable alternatives for PbS-based devices, and we hope that this study will inspire more studies on ALD of non-oxides on halide perovskites.

Atomic Layer Deposition of Metal Oxides and Chalcogenides for High Performance Transistors

“…Interest in applications of MCs and particularly TMCs within next‐generation electronics has risen steeply over the past decade, driven by their intrinsic layered crystal structures and unique properties. [ 193 , 209 ] TMCs typically consist of a metal/chalcogen atomic ratio of 1:2, although exceptions of 1:1, [ 210 , 211 ] and 2:3 [ 212 ] are possible. TMCs have three classical polymorphs, which are tetragonal (1T), hexagonal symmetry (2H), and rhombohedral (3R).…”

“…Aside from Mo, W, and Sn‐based MCs, the fabrication of alternative MC materials such as lead sulfide (PbS), manganese sulfide (MnS), and rhenium disulfide (ReS 2 ) is possible using ALD, [ 210 , 281 , 282 ] with their development for electronic applications attracting growing interest. [ 238 , 283 ] MnS, is a p‐type semiconductor with a wide bandgap of 3.7 eV, and it has been deposited with crystal phase‐control by ALD using bis(ethylcyclopentadienyl)Mn(II) (Mn(EtCp) 2 ) and H 2 S precursors.…”

“…Very recently, uniform and crystalline PbS thin‐films have been produced by low‐temperature ALD using rac‐N 2 ,N 3 ‐di‐tert‐butylbutane‐2,3‐diamide lead [Pb(dbda)] and bis(trimethylsilyl)‐amide lead [Pb(btsa) 2 ] as lead precursors, with H 2 S as a sulfur source. [ 210 ] The PbS films exhibited typical p‐type behaviors with excellent mobility up to 70 cm 2 V −1 s −1 . Lead chalcogenides are a well‐established class of ambipolar semiconductors, with carrier transport determined by an excess of either metal or chalcogen within the crystal structure.…”

Synthesis, Characterization, and Thermal Study of Divalent Germanium, Tin, and Lead Triazenides as Potential Vapor Deposition Precursors

“…Recently, PbS was deposited using the dicoordinated Pb–N bonded hexamethyldisilazide and cyclic diamide precursors, rendering near stochiometric films with low levels of carbon impurities. 29 However, the deposition temperature for ALD growth was limited to ≤155 °C due to the poor thermal stability of the deposited surface species. Volatility data have not been reported for the tetracoordinated Ge(II) and Pb(II) amidinates in the literature.…”

Synthesis, Characterization and Thermal Study of Divalent Germanium, Tin and Lead Triazenides for Atomic Layer Deposition

“…27,28 The amidinate ligand system provides a tetracoordinated, thermally stable and volatile precursors that afford high-quality SnS films with low levels of impurities. More recently, the first example of ALD grown PbS 29 using Pb-N bonded dicoordinated hexamethyldisilazide 25,30 and cyclic diamide 31 precursors.…”