Atomic Layer Deposition of p-Type Bi₂S₃

Abstract

Atomic layer deposition (ALD) of bismuth sulfide (Bi2S3) is demonstrated by the sequential exposure of bismuth­(III) bis­(2,2,6,6-tetramethylheptane-3,5-dionate) [Bi­(thd)3] and hydrogen sulfide (H2S) at 200 °C. A saturated growth rate of 0.34–0.37 Å/cycle was observed by in situ quartz crystal microbalance (QCM) and verified by ex situ X-ray reflectivity (XRR) measurements throughout the ALD temperature window. As-deposited Bi2S3 films were found to be polycrystalline in nature without any preferential orientation. In addition to the direct band gap at ca. 1.56 eV normally seen for Bi2S3, we also found evidence for an indirect band gap at ca. 1.03 eV. Ultraviolet photoelectron spectroscopy (UPS) and Seebeck measurements strongly support degenerate p-type conductivity of the as-grown thin films, in contrast to the n-type nature normally found in the literature. Temperature-dependent (70–300 K) electrical resistivity measurements showed that, in the temperature range of 70–100 K, variable-range hopping (VRH) is the dominant carrier-transport process whereas, above 100 K, clear deviations from the VRH transport equation were observed, implying a crossover from localized states to a band-like transport process.

Design of Ag Injection in Bi2S3 (AgBiS2) Thin Films for Photoelectrochemical Cell and Solar Cell Applications

“…x S 3-y (x= y= 0, 0.25, 0.50, 0.75 and 1) lms are given in gure 15. In the M-S plot, FTO/ Ag x Bi 2-x S 3-y (x= y= 0) thin lm shows a positive slope which con rms the 'n' type conductivity of the lm [49] whereas the rest of the lms exhibited negative slopes which con rmed the prepared lms are in 'p' type conducting nature as coinciding well with the observations made from Hall-effect analysis (table 2). The reason for the conversion of conductivity type in the lms (except x= y = 0) is attributed to the formation of acceptor defect between Ag and Bi.…”

Atomic Layer Deposition of Two-Dimensional Layered Materials: Processes, Growth Mechanisms, and Characteristics

“…191 Liu et al 43 first reported an ALD process for growing Bi 2 S 3 films via an R3 route. The crystalline Bi 2 O 3 films were first deposited via an ALD using Bi(thd) 3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) and H 2 O precursors at 300 C and were then converted to orthorhombic Bi 2 S 3 through a post-sulfurization process in sulfur vapor at 500 C. Subsequently, Mahuli et al 185 used Bi(thd) 3 and H 2 S to grow Bi 2 S 3 films directly via ALD in the range of 125 C-300 C. The GPC was constant (0.34-0.37 Å /cycle) in the range of 175 C-250 C. Otherwise, the GPC was lower at lower and higher temperatures, caused by either limited reactivity or increased desorption of precursors. The as-deposited Bi 2 S 3 films at 200 C were the polycrystalline orthorhombic phase with high purity.…”

Atomic layer deposition of stable 2D materials

“…Table 2 summarizes the main ALD conditions as well as the eventual applications of each 2D material. 154 These processes are performed at low to mid temperature (100-250 °C), expected for GeS ALD taking place near room temperature (50-75 °C). Indeed, in this case, desorption phenomenon occurs above 150 °C.…”