Synthesis of Micrometer Length Indium Sulfide Nanosheets and Study of Their Dopant Induced Photoresponse Properties Shinjita Acharya, † Mrinal Dutta, ‡ Suresh Sarkar, † Durga Basak, ‡ Supriyo Chakraborty, § and Narayan Pradhan* ,† † Centre for Advanced Materials & Department of Materials Science, ‡ Solid State Physics, § DST Unit of Nanoscience and Technology, Indian Association for the Cultivation of Science, Jadavpur, Kolkata * S Supporting Information ABSTRACT: Synthesis of various nanostructured semiconductor materials and processing them for different device fabrications has been at the forefront of research for the last two decades. In comparison to spherical nanoparticles, anisotropic materials e.g. nanorods, nanowires, and nanodisks have been widely explored to obtain a better performance of the devices. In addition, it is also well-known that nanomaterials, on doping with suitable impurities, can enhance the device sensitivity and speed. Combining both, we report here the synthesis of micrometer long In 2 S 3 nanosheets and on doping them with Cu(I), we have studied here their photoresponse properties. These nanosheets are synthesized in a high temperature colloidal method following a catalytic thermal decomposition of a single source precursor of In and S. From various TEM, HRTEM, and HAADF images the growth pattern of these sheets is investigated, and the obtained moire ́ fringes at the overlapped region are discussed. Finally, the comparative study of the device performance has been carried out with introducing different amounts of copper in these nanosheets. KEYWORDS: nanosheets, indium sulfide, doping, intrinsic vacancy, photodetector ■ INTRODUCTION Anisotropic semiconductor nanomaterials have generated a lot of interest in the field of materials science because of their unique patterning ability to influence the physical and electronic properties compared to the spherical particles in nanodimension. 1-4 Correlation between the colloidal synthesis of these anisotropic nanostructures and exploiting them for various applications ranging from optical to electronic remains in the frontier research area in recent days. 5-10 Among these, 2D semiconductor nanostructures are especially important because of their large surface area and long-range of lattice periodicity that provides a better channel for carrier trans- portation, enhancing the efficiency of the devices. 11-13 Hence, significant research emphasis is on the rise to synthesize such 2D nanostructures 14-19 and their implementations in various device based applications. 11,12 Over the past few years, group III-VI semiconductor nanomaterials, of which indium sulfide (In 2 S 3 ) has widely been studied as they are lucrative materials for catalysis, photovoltaics, and solar cells along with other optoelectronic device based applications. 20-22 In 2 S 3 exists in three different crystalline forms as a function of temperature: α-In 2 S 3 (defect cubic), β-In 2 S 3 (defect spinel), γ-In 2 S 3 (layered structure). 23 Among these, β-In 2 S 3 is an n-type semiconductor with a band gap of 2.0-2.3 eV which is the stable form at room temperature and exists in either cubic or tetragonal crystal structure 24-26 and manifests highly anisotropic crystal growth either along one or two dimensions. 14,25,27-31 Additionally, due to the defect spinel structure of β-In 2 S 3 , it acquires intrinsic vacant sites in the lattice; such vacancies exhibit electron affinity and can act as electron traps. 32 This interesting defect structure of β-In 2 S 3 has also paved the way for its application in photovoltaics. It is used in making green or red phosphors for color televisions, dry cells. Recently, it has also been reported that β-In 2 S 3 can replace highly toxic CdS in the buffer layer of solar cells with almost equivalent efficiency. 33-36 Hence, the fabrication and designing of different shapes of In 2 S 3 nanomaterials is highly desirable. There are several reports of β-In 2 S 3 in the literature with different morphologies like nanoplates, urchinlike micro- spheres, dendrites, hollow microspheres consisting of nano- flakes and nanobelts, porous 3D flowerlike structures and nanorods. 14,20,25,27-30,37-39 Recently, a report on the synthesis of highly uniform platelet shaped 2D nanostructure has appeared, 14 and after doping with Cu this has also been explored for the device fabrication. 11 Doping of different suitable foreign ions and creating an electron or hole carrier vacancy in the host has been a known phenomenon. 11,40 For In 2 S 3 , Cu + can act as an appropriate dopant with proper affinity for getting incorporated in its lattice to boost the electrical Received: January 27, 2012 Revised: April 22, 2012 Published: April 26, 2012 Article pubs.acs.org/cm © 2012 American Chemical Society 1779 dx.doi.org/10.1021/cm3003063 | Chem. Mater. 2012, 24, 1779-1785