Bismuth Doping of Germanium Nanocrystals through Colloidal Chemistry

Abstract

Nanogermanium is a material that has great potential for technological applications, and doped and alloyed Ge nanocrystals (NCs) are actively being considered. New alloys and compositions are possible in colloidal synthesis because the reactions are kinetically rather than thermodynamically controlled. Most of the Group V elements have been shown to be n-type dopants in Ge to increase carrier concentration; however, thermodynamically, Bi shows no solubility in crystalline Ge. Bi-doped Ge NCs were synthesized for the first time in a microwave-assisted solution route. The oleylamine capping ligand can be replaced by dodecanethiol without loss of Bi. A positive correlation between the lattice parameter and the concentration of Bi content (0.5–2.0 mol %) is shown via powder X-ray diffraction and selected area electron diffraction. X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), scanning TEM, and inductively coupled plasma–mass spectroscopy are consistent with the Bi solubility up to 2 mol %. The NC size increases with increasing amount of bismuth iodide employed in the reaction. Absorption data show that the band gap of the Bi-doped Ge NCs is consistent with the NC size. This work shows that a new element can be doped into Ge NCs via a microwave-assisted route in amounts as high as 1–2 mol %, which leads to increased carriers. Colloidal chemistry provides an inroad to new materials not accessible via other means.

Solution-based low-temperature synthesis of germanium nanorods and nanowires

“…Shifts of reflections in the XRD pattern should not be expected due to the similarity in size of Ga and Ge [35]. Similar to the observation of the unusually high Ga content in the here presented Ge NRs, low-temperature synthesis methods and kinetic process control can lead to the formation of metastable alloys with considerable metal incorporation in the Ge matrix, such as the Ge–Sn alloy [36–38] or efficient Bi incorporation in Ge nanocrystals [39]. The incorporation of the impurity dopants in the actual lattice should be investigated in detail using single-crystalline material and accumulation at twin planes should be excluded [40].…”

Surface coordination chemistry of germanium nanocrystals synthesized by microwave-assisted reduction in oleylamine

“…The Ge nanocrystals used here were synthesized by the microwave-assisted reduction of GeI 2 in oleylamine, without additional ligands or solvents, at a series of reaction temperatures (i.e., 210, 230, 250, and 270 °C) for 1 h. 1,19,27,28 The nanocrystal products all adopted the expected cubic structure of Ge, as assessed by powder X-ray diffraction, with nanocrystal sizes that increase with increasing reaction temperature (Figs. S4-S5 †).…”

Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19nanowires

“…Their electronic properties can be altered by incorporation of well-known dopants in the semiconductor host lattice, 7 – 9 while recently extraordinary high amounts of these known dopants as well as non-common metal incorporation in nanoscaled group IV elements is described. 10 – 13 To date, the performance of Si- and Ge-based materials in optics and photonics is limited by the dominating, intrinsic indirect bandgap of their thermodynamically most stable allotropes with diamond cubic crystal structures.…”