Narrow-gap physical vapour deposition synthesis of ultrathin SnS_1−xSe_x (0 ≤ x ≤ 1) two-dimensional alloys with unique polarized Raman spectra and high (opto)electronic properties

Abstract

Here we report ultrathin SnS1-xSex alloyed nanosheets synthesized via a narrow-gap physical vapour deposition approach. The SnS1-xSex alloy presents a uniform quadrangle shape with a lateral size of 5-80 μm and a thickness of several nanometers. Clear orthorhombic symmetries and unique in-plane anisotropic properties of the 2D alloyed nanosheets were found with the help of X-ray diffraction, high resolution transmission electron microscopy and polarized Raman spectroscopy. Moreover, 2D alloyed field-effect transistors were fabricated, exhibiting a unipolar p-type semiconductor behavior. This study also provided a lesson that the thickness of the alloyed channels played the major role in the current on/off ratio, and the high ratio of 2.10 × 102 measured from a large ultrathin SnS1-xSex device was two orders of magnitude larger than that of previously reported SnS, SnSe nanosheet based transistors because of the capacitance shielding effect. Obviously enhanced Raman peaks were also found in the thinner nanosheets. Furthermore, the ultrathin SnS0.5Se0.5 based photodetector showed a highest responsivity of 1.69 A W-1 and a short response time of 40 ms under illumination of a 532 nm laser from 405 to 808 nm. Simultaneously, the corresponding highest external quantum efficiency of 392% and detectivity of 3.96 × 104 Jones were also achieved. Hopefully, the narrow-gap synthesis technique provides us with an improved strategy to obtain large ultrathin 2D nanosheets which may tend to grow into thicker ones for stronger interlayer van der Waals forces, and the enhanced physical and (opto)electrical performances in the obtained ultrathin SnS1-xSex alloyed nanosheets prove their great potential in the future applications for versatile devices.

Optical phonons of SnSe(1−x)Sx layered semiconductor alloys

“…Therefore, the 632.8-nm excitation wavelength was chosen for most of the analysis. For SnSe (SnS), six modes are observed as expected: A g modes at 32, 70, 131 and 150 cm –1 (40, 95, 191, 219 cm –1 ) and B 3g at 37 and 109 cm –1 (49 and 164 cm –1 ), which are in agreement with previous studies on pure compounds 21 , 22 , 25 , 26 . For alloys, more than six peaks are resolved as shown in Fig.…”

“…Among 21 optical phonons, 2 are inactive, 7 infrared active, and 12 Raman active. The polarization dependence of the Raman intensity of each Raman active mode can be described by , where and represent the polarizations of the incident and scattered radiations at the position of scattering, and is the Raman tensor being expressed as 21 , 22 , 25 , 26 , …”

Substrate temperature dependent physical properties of SnS1−xSex thin films

“…However, with increase of substrate temperature (with decrease of S content in the films as noted from Table 2), there is a clear appearance of Raman modes of SnS and SnSe with a symmetric shape. A similar trend of the appearance of broad peaks in SnS 1−x Se x (0 ≤ x ≤ 1) alloyed nanosheets was reported by Wei Gao et al [29], who attributed this to the overlap of both SnS and SnSe peaks. Thomas Schnabel et al…”

Recent advances in low‐dimensional semiconductor nanomaterials and their applications in high‐performance photodetectors

“…In addition, there are three widely studied 2D layered metal chalcogenides, 24,25,39,[51][52][53][54][55][56][57][58][59][60] including III-VI compounds (such as InSe and GaS), IV-VI compounds (such as SnS and GeSe), and V-VI compounds (such as Sb 2 S 3 , Sb 2 Se 3 , and Bi 2 S 3 ). And, IV-VII group semiconductor layered material (eg, PbI 2 and so on) also widely studied.…”