A Low-Temperature Fabrication Method for WSe 2 Films Grown from Nanocrystalline Precursors
- PDF / 372,965 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 104 Downloads / 166 Views
A Low-Temperature Fabrication Method for WSe2 Films Grown from Nanocrystalline Precursors Christopher L. Exstrom1, Scott A. Darveau1, Joshua S. Edgar1, C.J. Curry1, Michael P. Hanrahan1, Qinglei Ma2, Matthew Hilfiker2, Aaron Ediger2, and Natale J. Ianno2 1
Department of Chemistry, University of Nebraska at Kearney, Kearney, NE 68849-1150,, U.S.A. 2
Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511, U.S.A. ABSTRACT WSe2 films have been fabricated using a low-temperature, two-step method involving the reaction of W(CO)6 and elemental selenium in refluxing (110 oC) toluene to form a nanocrystalline precursor consisting of amorphous tungsten and trigonal crystalline selenium. Drop cast or airbrush-deposited films of this precursor were annealed in an argon atmosphere using a two-step temperature ramp (250 oC for 15 min followed by 550 oC for 30 min). Raman and x-ray diffraction (XRD) characterization as well as the measured bandgaps of the resulting films are consistent with (002)-oriented WSe2 and are compared to the characterization of films produced via selenization of sputtered tungsten films in closed quartz tubes at 875 oC. INTRODUCTION Tungsten selenide (WSe2) is a crystalline semiconductor material that exhibits a layered 2dimensional (2D) hexagonal crystal structure with van der Waals’ gaps between Se-W-Se sandwiched layers, giving the material mechanical and electronic properties that show promising applications ranging from solid lubricants to solar cell absorbers. With its low mineral extraction costs [1], a reported direct bandgap of 1.35-1.5 eV [2] and high minority carrier mobility [3], the WSe2 material system is seeing renewed interest in next-generation solar cell absorber material development. Heterojunction photovoltaic devices based on WSe2 single-crystal absorbers have had reported efficiencies exceeding 8% [4]. We have recently reported PC1D simulations of a pWSe2 (1 Pm thickness)/n-WSe2 (50 nm) homojunction device with 10-24% efficiencies under 1.5AMG illumination when carrier lifetimes are varied from 1 ns to 1 Ps, respectively [5]. WSe2 films have been prepared using a variety of methods. Electrodeposition and chemical bath deposition methods have produced n-type films [6,7]. Laser ablation of WSe2.2 targets has produced films of varying Se/W ratios depending on the applied argon atmosphere pressures [8]. Solvent-assisted exfoliation of WSe2 powder has been employed to produce p-type selfassembled nanocrystal-based films less than 50 nm thick within hexane/ethylene glycol interfaces [9]. Selenization of sputtered tungsten films with elemental selenium has produced well-ordered WSe2 films upon heating at 450-550 oC [3,10-11]. However, long reaction times (24-120 h) are typically required and excess selenium must be removed from the sample using either a dynamic vacuum, inert gas flow, or a much higher-temperature post-annealing step.
2821 Downloaded from https:/www.cambridge.org/core. University of Arizona, on 25 May 2017 at 06:55:03, subj
Data Loading...
