Materials Science

Doping by Diffusion

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Science  04 Oct 2013:
Vol. 342, Issue 6154, pp. 17
DOI: 10.1126/science.342.6154.17-a

The electronic properties of bulk semiconductors can be improved by doping, the deliberate introduction of impurity atoms that increase the number or mobility of charge carriers. Usually, just doping the surface of a bulk semiconductor is sufficient, but for semiconductor nanocrystals, the entire particle needs to be doped to achieve the desired properties. Vlaskin et al. report on the doping of CdSe nanocrystals with Mn ions, a process that has proven especially difficult at the high levels desired to impart magnetic properties. Hot-injection synthesis of Mn-doped CdSe nanocrystals (where the particles rapidly form in solution from precursors) results in particles that are depleted in Cd2+ at the surface. The authors were able to incorporate Mn2+ ions uniformly by starting with CdSe seed nanocrystals, which were injected as a solution along with selenium into a solution of manganese acetate at ∼300°C for times varying from seconds to several hours. This thermodynamically controlled process, which uniformly increased the size of the seeds, resulted in diffusion doping of the entire crystal without requiring Cd2+ ion ejection and allowed doping levels of Mn2+ as high as 20% to be achieved.

J. Am. Chem. Soc. 135, 10.1021/ja4072207 (2013).

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