Stabilizing ultra-thin black phosphorus with in-situ-grown 1 nm-Al2O3 barrier

Abstract

Exfoliated black phosphorus is a 2D semiconductor with promising properties for electronics, spintronics, and optoelectronics. Nevertheless, its rapid degradation in air renders its integration and use in devices particularly challenging—even more so for smaller thicknesses for which the degradation rate is tremendously enhanced. In order to effectively protect the thinnest flakes, we present here an approach based on an in-situ dielectric capping to avoid all contact with air. Optical microscopy, Raman spectroscopy, and atomic force microscopy studies confirm that 1 nm of Al2O3 efficiently passivates exfoliated black phosphorus (below 5 layers) on Si/SiO2 substrates. Such an ultrathin and transparent passivation layer can act as a tunnel barrier allowing for black phosphorus devices processing without passivation layer removal.

Effective passivation of black phosphorus transistor against ambient degradation by an ultra-thin tin oxide film

“…2d. After exposure in air for 15 days, the pure BP FET (without passivation) is nonconducting at any backgate voltage, which indicates the BP channel is completely destroyed by H 2 O/O 2 in air as reported by many previous works [20,26]. While the SnO 2 -passivation BP FET maintains the typical p-type transfer characteristics without visible performance degradation even after exposure in air for 15 days, which reflects that the SnO 2 passivation can provide long-term stability for layered BP materials.…”

“…For the layered BP exposed to air, oxygen will be adsorbed on the surface and converted to oxygen ionize under the influence of light, and oxygen ionizes will react with BP and produce phosphoric oxide, which reacts with H 2 O in the air [16,17]. The above process is repeated to cause the ambition degradation of the BP, and then leads to severe instability in BP devices [18][19][20]. Therefore, the effective surface passivation of BP is necessary to suppress the degradation of a BP device during the fabricating process and even after fabrication.…”

“…The main reason for effective passivation is that continuous SnO 2 film is an effective barrier to water vapor penetration [30]. As is well known, it was the oxygenated H 2 O in ambient to destroy structure of BP and then lead to permanent degradation [20]. The surface of layered BP firstly reacts with oxygen in the air, and the formed PO x will react with water to form corrosive phosphoric acid.…”

Spectral Responsivity and Photoconductive Gain in Thin Film Black Phosphorus Photodetectors

“…Given that BP is unstable in air in particular with the presence of both oxygen and water 43 , an effective passivation technique is essential. Here, the devices are encapsulated with a thin layer of Al2O3 which reduces degradation of the BP active layer 44 . Figure 1d shows the transfer characteristic of the 30 nm-thick device measured under ambient conditions at a source-drain voltage, VDS = 1 mV.…”

Hybrid nanocomposites of 2D black phosphorus nanosheets encapsulated in PMMA polymer material: new platforms for advanced device fabrication

“…Several materials have been used so far for this purpose, ranging from other van der Waals materials 15,16 to inert oxides. [17][18][19] Polymers have been as well identified as a low cost, easy, and efficient method to preserve multilayer bP quality, 20 and in particular poly (methyl methacrylate) (PMMA) has been widely used for this purpose. 21 This is very convenient, since PMMA is also the most common resist for electron beam lithography (EBL), which is a widely used technique to design prototypical devices for electrical, optical, and thermal transport applications.…”