Ultrathin two-dimensional (2D) nanomaterials are a highly promising new class of materials that are revealing exotic properties with great promise for application in next generation electronics and optoelectronic devices. Recently, significant progress has been demonstrated in semiconducting ultrathin nanosheet-based electronics and optoelectronics.The mobility of a single-layer MoS2 transistor was improved to ~ 200 cm~2V~(-1)s~(-1) by using a high k dielectric layer of hafnium oxide.1 Photodetectors made from inorganic semiconducting ultrathin nanosheets, analogues to graphene, could show enhanced responsivity and spectral selectivity. A single-layer MoS2-based photodetector was recently demonstrated with an improved spectral responsivity of 7.5 mAW~(-1) compared to similar graphene-based photodetectors (~1 mAW~(-1)). Materials based on III-VI layered metal chalcogenides (LMCs) such as GaS and GaSe have distinct structural, electronic and optical properties for optoelectronic device applications. Interlayer interactions in these layered materials are dominated by the weak van der Waals force, while interlayer-bonding forces are covalent in nature. For example, GaS is considered as a promising material for near-blue light emitting devices because it has an indirect band gap at 2.59 eV at 300 K and a direct band gap at approximately 3.05 eV, Crystalline single-layer or few-layer GaS, GaSe nanosheets can be efficiently obtained using a mechanical cleavage approach, and subsequently transferring to SiO2/Si wafer and other substrates. Ultrathin GaS and GaSe bottom-gate transistors with mobilities of 0.1 cm ~2V~(-1)s~(-1) have been demonstrated by Dravid et al7. However, comparable ultrathin GaS-based photodetectors have not been previously reported.
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