Controlled Growth of Large‐Sized and Phase‐Selectivity 2D GaTe Crystals

Abstract

Since the first discovery of graphene obtained by mechanical exfoliation (ME) in 2004, [1] 2D layered materials have been widely investigated due to their unique electrical, optical, and mechanical properties at the single atomic thickness. [2,3] In the past decade, substantial progress has been made toward the use of 2D materials for next-generation electronic devices, [4] GaTe has recently attracted significant interest due to its direct bandgap and unique phase structure, which makes it a good candidate for optoelectronics. However, the controllable growth of large-sized monolayer and few-layer GaTe with tunable phase structures remains a great challenge. Here the controlled growth of large-sized GaTe with high quality, chemical uniformity, and good reproducibility is achieved through liquid-metal-assisted chemical vapor deposition method. By using liquid Ga, the rapid growth of 2D GaTe flakes with high phase-selectivity can be obtained due to its reduced reaction temperature. In addition, the method is used to synthesize many Ga-based 2D materials and their alloys, showing good universality. Raman spectra suggest that the as-grown GaTe own a relatively weak van der Waals interaction, where monoclinic GaTe displays highly-anisotropic optical properties. Furthermore, a p-n junction photodetector is fabricated using GaTe as a p-type semiconductor and 2D MoSe 2 as a typical n-type semiconductor. The GaTe/MoSe 2 heterostructure photodetector exhibits large photoresponsivity of 671.52 A W −1 and high photo-detectivity of 1.48 × 10 10 Jones under illumination, owing to the enhanced light absorption and good quality of as-grown GaTe. These results indicate that 2D GaTe is a promising candidate for electronic and photoelectronic devices.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202007909. optoelectronic devices, [5] sensors, [6] catalytic, [7] etc. [8] Among all 2D materials reported so far, graphene has been most intensely studied because of its large electron and hole mobilities. However, its zero band-gap hinders its applications for optoelectronic devices. [1,9] 2D transition metal dichalcogenides, such as MoS 2 , are another candidate for electronic and optical applications due to its direct bandgap nature when thinned down to monolayer. However, monolayer MoS 2 devices exhibit low carrier mobility and slow photoresponse, [10] and multilayer MoS 2 -based photodetectors have small photo-responsivity due to its indirect bandgap nature. [11] Black phosphorus (BP) has a thicknessdependent direct bandgap in the range of ≈0.3-2.0 eV, which shows both high carrier mobility and large photo-responsivity. Doping BP with other elements (such as, As, Sb, Te, Bi, Se, S, etc.) can further tune their electronic and optical properties. [12,13] Whereas BP and doped-BP are not stable in ambient conditions, and few-layer BP cannot be obtained by conventional chemical vapor deposition (CVD) methods, which limit their applications in various areas.Different fr...

Monotonous alloying-driven band edge emission in two-dimensional hexagonal GaSe1−xTex semiconductors for visible to near-infrared photodetection

“…[4][5][6] On the other hand, the m-GaTe phase is more thermodynamically stable than the h-GaTe phase; thus, it is commonly observed in epitaxial growth such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and molecular beam epitaxy (MBE). [7][8][9] For instance, Huynh et al have demonstrated diversity of the 2D-GaTe nanostructures on GaAs (001) substrates by MBE. Interestingly, the study has proposed a great selectivity to achieve single-phase h-GaTe as deposited on the GaN/sapphire substrate.…”

Molecular Beam Epitaxy of Two-Dimensional GaTe Nanostructures on GaAs(001) Substrates: Implication for Near-Infrared Photodetection

“…10 Note that the broadening in linewidth of these peaks in the spectrum of the 350 °C sample could be due to its poor crystal quality, as discussed in the following section. This kind of spectrum assumedly points to the dominant existence of the h-GaTe phase in the film 8,9,16 in considering a low density of m-GaTe nanorods as observed from SEM images (Figure 1a,b). As T g gets higher than 400 °C, the m-GaTe characteristic peaks positioned at ∼58, 64, 74, 109, 114, 161, 172, 196, 209, 270, and 285 cm −1 were more and more visible.…”

“…The Raman spectrum of the 15 min sample (Figure 5e) is well recognized with the thoroughly dominant phonon modes at ∼126 and ∼141 cm −1 , similar to that of the GaTe/GaN/sapphire sample (Figure 4e) or ultrathin single-crystal h-GaTe flakes in most recent studies using other growth methods. 8,16 Accordingly, it is worth noting that this motif of the Raman pattern featured by these phonon modes may represent either the presence of single-phase h-GaTe nanostructures or the lateral h/m-mixed GaTe phase in a structural thin film.…”

“…Generally, diversification in the structural phase of epitaxial 2D GaTe is more pronounced among 2D materials, leading to much complexity but more attraction of their physical behaviors. Although 2D GaTe nanomaterials have been epitaxially synthesized by chemical vapor deposition (CVD) ,, and physical vapor deposition (PVD) methods in recent years, , these techniques are still facing several challenges such as high degrees of impurities as growing in a low-vacuum chamber, nonuniformity on a large-scale area, randomly localized deposition on the substrate surface, and possible formation of the undesired Ga 2 O 3 phase . On the other hand, molecular beam epitaxy (MBE) that offers highly uniform and purified thin films on a wafer scale was employed to synthesize 2D GaTe in few studies. , Nevertheless, the structural phase controllability of 2D GaTe in this growth technique has been limited for investigation due to certain challenges in purifying the h-GaTe phase.…”

“…Although 2D GaTe nanomaterials have been epitaxially synthesized by chemical vapor deposition (CVD) 11,16,17 and physical vapor deposition (PVD) methods in recent years, 8,12 these techniques are still facing several challenges such as high degrees of impurities as growing in a low-vacuum chamber, nonuniformity on a large-scale area, randomly localized deposition on the substrate surface, and possible formation of the undesired Ga 2 O 3 phase. 16 On the other hand, molecular beam epitaxy (MBE) that offers highly uniform and purified thin films on a wafer scale was employed to synthesize 2D GaTe in few studies. 18,19 Nevertheless, the structural phase controllability of 2D GaTe in this growth technique has been limited for investigation due to certain challenges in purifying the h-GaTe phase.…”