Study of Oxidation and Polarization-Dependent Optical Properties of Environmentally Stable Layered GaTe Using a Novel Passivation Approach.

Kotha Kotha,Tuschel Tuschel,Gallis Gallis,Murray Murray

doi:10.3390/nano9111510

Kotha Kotha, Tuschel Tuschel + Show 2 more

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https://doi.org/10.3390/nano9111510

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Abstract

Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered promising layered semiconductors that can serve as vital building blocks towards the implementation of nanodevices in the fields of nanoelectronics, optoelectronics, and quantum photonics. However, oxidation-induced electronic, structural, and optical changes observed in ambient-exposed gallium chalcogenides need to be further investigated and addressed. Herein, we report on the thickness-dependent effect of air exposure on the Raman and photoluminescence (PL) properties of GaTe flakes, with thicknesses spanning in the range of a few layers to 100 nm. We have developed a novel chemical passivation that results in complete encapsulation of the as-exfoliated GaTe flakes in ultrathin hydrogen–silsesquioxane (HSQ) film. A combination of correlation and comparison of Raman and PL studies reveal that the HSQ-capped GaTe flakes are effectively protected from oxidation in air ambient over the studied-period of one year, and thus, preserving their structural and optical characteristics. This contrasts with the behavior of uncapped GaTe, where we observe a significant reduction of the GaTe-related PL (~100×) and Raman (~4×) peak intensities for the few-layered flakes over a period of few days. The time-evolution of the Raman spectra in uncapped GaTe is accompanied by the appearance of two new prominent broad peaks at ~130 cm−1 and ~146 cm−1, which are attributed to the formation of polycrystalline tellurium, due to oxidation of ambient-exposed GaTe. Furthermore, and by leveraging this novel passivation, we were able to explore the optical anisotropy of HSQ-capped GaTe flakes. This is caused by the one-dimensional-like nature of the GaTe layer, as the layer comprises Ga–Ga chains extending along the b-axis direction. In concurrence with high-resolution transmission electron microscopy analysis, polarization-dependent PL spectroscopy was used to identify the b-axis crystal direction in HSQ-capped GaTe flakes with various thicknesses over a range of wavelengths (458 nm–633 nm). Thus, our novel surface-passivation offers a new approach to explore and reveal the physical properties of the layered GaTe, with the potential of fabricating reliable polarization-dependent nanophotonics with structural and optical stability.

Highlights

A recent surge of interest in two-dimensional (2D) layered semiconductors [1], such as metal chalcogenides (MCs), is attributed to their remarkable properties, which established them as a distinct class of materials with the potential for immense technological applications in the fields of electronics [2], optoelectronics [3,4], sensing [5,6] and quantum information technology [7,8]
Raman spectroscopy was explored for the identification of the b-axis, but the results revealed a dependence on both the thickness and excitation laser wavelength
We observed that the intensity of the Ag-Raman peak around 115 cm−1 for the 10 nm flake is higher as compared with the 40 nm flake, which can be explained considering optical interference effects of the stacked gallium telluride (GaTe)/SiO2/Si materials [24]

Summary

Introduction

A recent surge of interest in two-dimensional (2D) layered semiconductors [1], such as metal chalcogenides (MCs), is attributed to their remarkable properties, which established them as a distinct class of materials with the potential for immense technological applications in the fields of electronics [2], optoelectronics [3,4], sensing [5,6] and quantum information technology [7,8]. GaTe is typically a p-type material, with each monolayer comprising a Te-Ga-Ga-Te assembly (Figure 1), adding to the set of candidate layered semiconductors for the fabrication of van der Waals heterostructures and devices [10,12,13]. Recent reports have opened a whole new world of exciting opportunities for the use of mechanically-exfoliated and CVD-grown GaTe in van der Waals heterostructure nanoelectronics [13] in nonlinear optics applications [14], in radiation detectors [15], and in optoelectronics, such as in photodetectors, due to the high photoresponsivity (104 A/W) and short response time (6 ms) demonstrated in layered GaTe [16,17]

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