Novel electronic devices based upon nanotechnology may soon be realized due to a new understanding of how impurities, or dopants, can be intentionally incorporated into semiconductor nanocrystals. This understanding, announced today by researchers at the Naval Research Laboratory (NRL) and the University of Minnesota (UMN), should help enable a variety of new technologies ranging from high-efficiency solar-cells and lasers to futuristic spintronic and ultra-sensitive biodetection devices. The complete findings of the study are published in the July 7, 2005, issue of the journal Nature.
Nanocrystals are tiny semiconductor particles just a few millionths of a millimeter across. Due to their small size, they exhibit unique electronic, optical, and magnetic properties that can be utilized in a variety of technologies. To move toward this end, chemical methods have been optimized over the last 20 years to synthesize extremely pure nanocrystals. More problematic, however, has been the goal of controllably incorporating selected impurities into these particles. Conventional semiconductor devices, such as the transistor, would not operate without such impurities. Moreover, theory predicts that dopants should have even greater impact on semiconductor nanocrystals. Thus, doping is a critical step for tailoring their properties for specific applications.
A long-standing mystery has been why impurities could not be incorporated into some types of semiconductor nanocrystals. The findings by NRL and UMN researchers establish the underlying reasons for these difficulties, and provide a rational foundation for resolving them in a wide variety of nanocrystal systems. "The key lies in the nanocrystals surface," said Dr. Steven Erwin, a physicist at NRL and lead theorist on the project. "If an impurity atom can stick, or adsorb, to the surface strongly enough, it can eventually be incorporated into the nanocrystal as it grows. If the impurity binds to the nanocrystal surface too weakly, or if the strongly binding surfaces are only a small fraction of the total, then doping will be difficult." From calculations based on this central idea, the team could predict conditions favorable for doping. Experiments at UMN then confirmed these predictions, including the incorporation of impurities into nanocrystals that were previously believed to be undopable. Thus, a variety of new doped nanocrystals may now be possible, an important advance toward future nanotechnologies.
Donna McKinney | EurekAlert!
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