Field–effect transistors made of individual colloidal PbS nanosheets

Abstract

Two-dimensional materials are considered for future quantum devices and are usually produced by extensive methods like molecular beam epitaxy. We report on the fabrication of field-effect transistors using individual ultra-thin lead sulfide nanostructures with lateral dimensions in the micrometer range and a height of a few nanometers as conductive channel produced by a comparatively fast, inexpensive, and scalable colloidal chemistry approach. Contacted with gold electrodes, such devices exhibit p-type behavior and temperature-dependent photoconductivity. Trap states play a crucial role in the conduction mechanism. The performance of the transistors is among the ones of the best devices based on colloidal nanostructures.Inexpensive electronic applications require semiconductor materials which can be easily processed, e.g. by spin-coating or dip-coating [1]. Thus, researchers are looking for materials that are solution processable while exhibiting reasonable electronic properties. Colloidal semiconductor nanoparticles are among the candidates to be integrated into low-cost electronic devices [2]. They are suspended in liquid media, mass-producible, and tunable in their optical and electrical properties due to quantum confinement effects [3]. Colloidal nanomaterials are promising due to the simplicity and thus the inexpensiveness of their production and subsequent processing. One hurtle which needs to be overcome is the presence of tunnel barriers in the nanoparticle films which lead to high resistances. This effect is the consequence of long isolating organic ligands capping the nanoparticles surface. These ligands can be either replaced by shorter ones including halides [4], or removed by physicochemical processes [5]. These post-treatments deteriorate the nanoparticle surface but reduce the resistive power losses. A different approach to reduce the tunnel barriers consists in the use of inorganic capping "ligands" such as In 2 Se 2− on CdSe nanoparticles [6]. Such films find applications e.g. as field-effect transistors [7], thermoelectrics [8], and photoconductors [9].Yet another approach is to avoid tunnel barrier from the beginning on and to synthesize continuous twodimensional materials in solution. Indeed, some progress has been made in controlling the lateral dimensions [10] and thickness [11] of nanostructures through varying parameters like the nature of the ligands which are used to bind to specific facets of the nanocrystals and inhibit an isotropic growth [12]. Recently, we demonstrated that two-dimensional PbS nanosheets can be produced in solution by colloidal chemistry [13]. We showed that lead sulfide nanosheets form due to two-dimensional oriented attachment of small zero-dimensional colloidal nanocrystals. The nanosheets have a height of a few nanometers and exhibit lateral dimensions in the order of a micron. Nevertheless, the control of anisotropic growth in nanocrystal syntheses is still a great challenge. The PbS nanosheets used in the here presented study were synthesized based on the rec...

Tailoring the Height of Ultrathin PbS Nanosheets and Their Application as Field-Effect Transistors

“…In order to demonstrate the power of the synthesis we prepared field‐effect transistors (FETs) made of PbS nanosheets of various thickness. Recently, we reported on PbS nanosheet field‐effect transistors which outperformed the best state‐of‐the‐art colloidal materials in their pristine form . Those individual PbS nanosheet FETs contacted by symmetrical gold‐contacts showed p‐type behavior and a modest transfer characteristic at room temperature whereas at lower temperatures they exhibited a pronounced p‐type characteristic.…”

Phototransport in colloidal nanoplatelets array

“…Moreover, the 2D aspect of the nanoparticles leads to a high exciton binding energy [7,8] (≈250 meV) and a fast photoluminescence lifetime. While the spectroscopic properties have attracted huge interest in particular for stimulated emission, the integration of NPL [9] into conductive devices remains far less investigated [10,11]. Nevertheless, NPL look promising because their sharp optical features can be used to develop narrow emission electroluminescence devices [12] or photodetectors with finely controlled cut-off wavelengths.…”

The Role of Halogens in the Synthesis of Semiconductor Nanocrystals

“…In the case of PbS NCs, since also TOP is used as solvent for the sulphur source, the influence of DCE might also release chloride anions, although the reaction temperature is much lower (100 ∘ C). Additionally, in this case, the presence of acetate anions may also play a role in the final NCs shape and may also compete for different crystallographic facets during the evolution of the reaction, which is the topic of on-going investigations, including the use of these sheets as transistors [50].…”