Doping semiconductor nanocrystals

Abstract

Doping--the intentional introduction of impurities into a material--is fundamental to controlling the properties of bulk semiconductors. This has stimulated similar efforts to dope semiconductor nanocrystals. Despite some successes, many of these efforts have failed, for reasons that remain unclear. For example, Mn can be incorporated into nanocrystals of CdS and ZnSe (refs 7-9), but not into CdSe (ref. 12)--despite comparable bulk solubilities of near 50 per cent. These difficulties, which have hindered development of new nanocrystalline materials, are often attributed to 'self-purification', an allegedly intrinsic mechanism whereby impurities are expelled. Here we show instead that the underlying mechanism that controls doping is the initial adsorption of impurities on the nanocrystal surface during growth. We find that adsorption--and therefore doping efficiency--is determined by three main factors: surface morphology, nanocrystal shape, and surfactants in the growth solution. Calculated Mn adsorption energies and equilibrium shapes for several nanocrystals lead to specific doping predictions. These are confirmed by measuring how the Mn concentration in ZnSe varies with nanocrystal size and shape. Finally, we use our predictions to incorporate Mn into previously undopable CdSe nanocrystals. This success establishes that earlier difficulties with doping are not intrinsic, and suggests that a variety of doped nanocrystals--for applications from solar cells to spintronics--can be anticipated.

Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy

“…However, it can also be a problem in other applications, for example, optoelectronic devices such as light emitting diodes [12] and solar-cell [13][14] devices, since surface states are created within the band gap region either because of surface inhomogeneities like nonstoichiometry or because of the selective adsorption of foreign species in addition to the abrupt termination of lattice periodicity. Such surface states will strongly influence the electronic and optical properties at the semiconductor surfaces and interfaces since the surface recombination rate may become dominating, resulting in a short carrier life time [15][16][17][18]. The potential implications of these effects are especially noticeable in the case of nanostructured materials.…”

Single-exciton spectroscopy of single Mn doped InAs quantum dots

“…[9][10][11] These systems can also be used as a reference to interpret the experiments on Mn doped nanocrystals. 12,13 The focus of this work is the single exciton spectroscopy of a single Mn atom in a InAs quantum dot ͑QD͒, motivated by recent experimental results on InAs QD ͑Ref. 8͒ and keeping in mind the relation to previous experiments on single Mn doped CdTe.…”

Surfactant‐Assisted Synthesis of Co‐ and Li‐Doped ZnO Nanocrystalline Samples Showing Room‐Temperature Ferromagnetism

“…During the aggregation of crystallite size it is reasonable to speculate that the doped magnetic ions gets randomized in the host matrix in view of the literature reports that the presence of surfactant reduces interfacial tension between the host and the dopant. [25,26] This probably inhibits the clustering of the dopant ions facilitating the randomization of Co atoms in the ZnO lattice. This is schematically illustrated in Fig.4.…”