Tunable Electrical Properties of Vanadium Oxide by Hydrogen-Plasma-Treated Atomic Layer Deposition

Abstract

In this study, a plasma-modified process was developed to control the electrical properties of atomic layer deposition (ALD)-grown vanadium dioxide (VO 2 ), which is potentially useful for applications such as resistive switching devices, bolometers, and plasmonic metamaterials. By inserting a plasma pulse with varying H 2 gas flow into each ALD cycle, the insulator-to-metal transition (IMT) temperature of postdeposition-annealed crystalline VO 2 films was adjusted from 63 to 78 °C. Film analyses indicate that the tunability may arise from changes in grain boundaries, morphology, and compositional variation despite hydrogen not remaining in the annealed VO 2 films. This growth method, which enables a systematic variation of the electronic behavior of VO 2 , provides capabilities beyond those of the conventional thermal ALD and plasma-enhanced ALD.

Growth without Postannealing of Monoclinic VO2 Thin Film by Atomic Layer Deposition Using VCl4 as Precursor

“…Various techniques had been employed for preparing VO 2 films, including the sol-gel method [22,23], electron-beam evaporation [25,26], sputtering [5,17], pulsed laser deposition (PLD) [27,28], molecular beam epitaxy (MBE) [16,29], chemical vapor deposition (CVD) [30][31][32][33][34], and atomic layer deposition (ALD) [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]. Among them, ALD is an excellent technique which has drawn much attention due to its many advantages, including preparation of the highly conformal thin films with almost 100% step coverage, accurate control of film thickness at the atomic scale, low growth temperature, and wide-area uniformity.…”

“…Generally, organic vanadium compounds are employed as ALD precursors and reacted with H 2 O or O 3 to grow vanadium oxide thin films, such as tetrakis(ethylmethylamino)vanadium (TEMAV) [35][36][37][38][39][40][41][42], vanadyl isopropoxide (VTIP) [43][44][45][46], and vanadyl triisopropoxide (VTOP) [47][48][49][50]. However, the organic precursors (TEMAV, VTIP, and VTOP) are only suitable for low process temperatures in ALD because the decomposition temperatures of TEMAV, VTIP, and VTOP are about 175 [35,40], 200 [43], and 180 • C [49,50], respectively.…”

“…Therefore, the as-deposited vanadium oxide films grown by ALD from organic vanadium precursors are generally reported to have amorphous structures with no significant SMT behavior and a postannealing process is necessary for converting the amorphous to crystalline VO 2 . Previous studies have reported that postannealing in N 2 , He, O 2 , or N 2 /O 2 mixed gas with a low O 2 partial pressure resulted in crystalline monoclinic VO 2 for the temperature range of 425-585 • C [35][36][37][38][39][40][41][42]. Since the extra postannealing process is necessary to obtain a crystalline VO 2 , it results in higher manufacturing costs and increases the failure possibilities of the process and products.…”

Transparent Electrodes Consisting of a Surface‐Treated Buffer Layer Based on Tungsten Oxide for Semitransparent Perovskite Solar Cells and Four‐Terminal Tandem Applications

“…Evaporated transition metal oxides are known to become sensitive to their environment, since they are often not stoichiometric due to the oxygen deficiency, [ 27–29 ] which has been confirmed by X‐ray photoelectron spectroscopy (XPS) results for the thermally evaporated metal oxide buffer layers, WO x , WO x /NbO y , and NbO y . As shown in Figure S10, Supporting Information, the XPS peaks of these buffer materials are compared to the stoichiometric single‐crystalline films WO 3 and Nb 2 O 5 , denoted by the vertical lines.…”

“…Transition metal oxides that are evaporated especially become sensitive to their environment, since they are often not stoichiometric due to oxygen deficiency. [ 27–29 ] However, the presence of these oxygen vacancies creates structural defects in the band gaps, which enable hole injection properties despite their n‐type behavior. [ 27 ] Previous reports on n‐i‐p perovskite solar cell structures commonly demonstrated the use of molybdenum oxide (MoO x ) as the sputter buffer (Table S1, Supporting Information), but usually result in low fill factor (FF) values.…”