Effect of Oxygen Source on the Various Properties of SnO2 Thin Films Deposited by Plasma-Enhanced Atomic Layer Deposition

Abstract

Herein, we performed a comparative study of plasma-enhanced atomic layer deposition (PEALD) of SnO2 films using Sn(dmamp)2 as the Sn source and either H2O plasma or O2 plasma as the oxygen source in a wide temperature range of 100–300 °C. Since the type of oxygen source employed in PEALD determines the growth behavior and resultant film properties, we investigated the growth feature of both SnO2 PEALD processes and the various chemical, structural, morphological, optical, and electrical properties of SnO2 films, depending on the oxygen source. SnO2 films from Sn(dmamp)2/H2O plasma (SH-SnO2) and Sn(dmamp)2/O2 plasma (SO-SnO2) showed self-limiting atomic layer deposition (ALD) growth behavior with growth rates of ~0.21 and 0.07–0.13 nm/cycle, respectively. SO-SnO2 films showed relatively larger grain structures than SH-SnO2 films at all temperatures. Interestingly, SH-SnO2 films grown at high temperatures of 250 and 300 °C presented porous rod-shaped surface morphology. SO-SnO2 films showed good electrical properties, such as high mobility up to 27 cm2 V−1·s−1 and high carrier concentration of ~1019 cm−3, whereas SH-SnO2 films exhibited poor Hall mobility of 0.3–1.4 cm2 V−1·s−1 and moderate carrier concentration of 1 × 1017–30 × 1017 cm−3. This may be attributed to the significant grain boundary and hydrogen impurity scattering.

Influence of the Curing and Annealing Temperatures on the Properties of Solution Processed Tin Oxide Thin Films

“…A lower value was previously attributed to lesser dense films [24]. We previously reported the density of a-SnO x to be 5.29 g/cm 3 [6], a value smaller than the handbook value of 6.45 g/cm 3 [24,45]. Relating to the TGA data, up to 400 • C the material mass loss is less than 10%, but at 492 • C, ~78% of the total mass is lost, denoting the poor reactivity of the material at a temperature below 400 • C [43,46].…”

“…The maximum refractive index in the visible region is 2 to 2.8 for polycrystalline SnO 2 , and above 3 for amorphous tin oxide. The refractive index taken at 1.95 eV (corresponding to a wavelength of 633 nm) [24] has a value of 1.5 to 1.7, which is smaller than the reference handbook value of 2.06 eV [45]. A lower value was previously attributed to lesser dense films [24].…”

“…The refractive index taken at 1.95 eV (corresponding to a wavelength of 633 nm) [24] has a value of 1.5 to 1.7, which is smaller than the reference handbook value of 2.06 eV [45]. A lower value was previously attributed to lesser dense films [24]. We previously reported the density of a-SnO x to be 5.29 g/cm 3 [6], a value smaller than the handbook value of 6.45 g/cm 3 [24,45].…”

“…For large area electronics, vacuum processing is usually preferred due to the high yield production. In vacuum processing, the substrate temperature, the partial pressure, and/or the total pressure are processing parameters before the annealing step [22][23][24]. However, vacuum processing requires high investments and maintenance costs.…”

“…For perovskite solar cells, plasma assisted atomic layer deposition of SnO 2 led to crystallite sizes of ~25 nm, a carrier concentration in the 10 19 cm −3 range, and mobilities of 35 cm 2 /Vs [20]. SnO 2 fabricated by PEALD had crystals in the ~50 nm range size, bandgaps of 3.95 eV, a Hall mobility of 27 cm 2 /Vs, and a carrier concentration of 4 × 10 19 cm −3 [24].…”