From Impurity Doping to Metallic Growth in Diffusion Doping: Properties and Structure of Silver-Doped InAs Nanocrystals

Abstract

Tuning of the electronic properties of pre-synthesized colloidal semiconductor nanocrystals (NCs) by doping plays a key role in the prospect of implementing them in printed electronics devices such as transistors, and photodetectors. While such impurity doping reactions have already been introduced, the understanding of the doping process, the nature of interaction between the impurity and host atoms, and the conditions affecting the solubility limit of impurities in nanocrystals are still unclear. Here, we used a post-synthesis diffusion based doping reaction to introduce Ag impurities into InAs NCs. Optical absorption spectroscopy along with analytical inductively coupled plasma mass-spectroscopy (ICP-MS) were used to present a two stage doping model consisting of a "doping region" and a "growth region", depending on the concentration of the impurities in the reaction vessel. X-ray absorption fine-structure (XAFS) spectroscopy was employed to determine the impurity location and correlate between the structural and electronic properties for different sizes of InAs NCs and dopant concentrations.The resulting structural model describes a heterogeneous system where the impurities initially dope the NC, by substituting for In atoms near the surface of the NC, until the "solubility limit" is reached, after which the rapid growth and formation of metallic structures are identified.

Identification of dopant site and its effect on electrochemical activity in Mn-doped lithium titanate

“…at the atomistic level opens up new opportunities for their rational design [1-4]. In many materials with advanced optical, magnetic, electronic, mechanical, and catalytic properties, new functionalities arise due to changes in local environment and electronic structure with doping or substitution [5-10]. The AB 2 O 4 type spinel lithium titanate (Li 4/3 Ti 5/3 O 4 , or LTO) is a promising anode material for Li-ion batteries (LIBs).…”

InAs Nanocrystals with Robust p‐Type Doping

“…We note that a similar effect—a relatively low change in the In and As K‐edge XAFS data with Ag doping—indicated, too, a substitutional (as opposed to interstitial) doping location at the NC surface. [ 48 ]…”

“…Recently, we demonstrated the effect of n‐type impurity doping of InAs NCs in field effect transistors, [ 47 ] by implementing a post‐synthesis doping reaction with Cu. [ 21,47–50 ] The Cu‐doped‐InAs NCs FETs showed improved performance over the intrinsic InAs films due to electron donating impurity sub‐band, in line with the n‐type doping characteristics at the individual nanocrystal level. [ 21,49,51 ] However, the fabrication of p‐type InAs NCs FETs is challenging as one has to overcome the intrinsic excess free electrons of as‐synthesized InAs NCs.…”

Chloride and Indium‐Chloride‐Complex Inorganic Ligands for Efficient Stabilization of Nanocrystals in Solution and Doping of Nanocrystal Solids

“…Unfortunately, with the available techniques we were not able to elucidate the predominant location of the impurities either on sites at the surface of the NCs or their substitutional or interstitial incorporation in the host CdSe lattice, which is difficult due to the low concentration of the dopants. Further studies will be needed to determinate the local structure around the indium (chlorine) dopants which requires more sophisticated methods . But based on the results of In‐doped CdSe NCs presented by the Murray, the Norris, and the Talapin groups, one can assume that the indium species most likely have a diverse heterogeneous surrounding where some of them are substitutional dopants and others occupy the surface of the NCs, providing the doping and surface state passivation.…”