Home > Press > Discovery of 'Doping' Mechanism in Semiconductor Nanocrystals
Abstract:
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 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 nanocrystal's 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.
According to Dr. David Norris, an Associate Professor of Chemical Engineering and Materials Science at UMN and the lead experimentalist on the team, "an exciting aspect of these results is that they overturn a common belief that nanocrystals are intrinsically difficult to dope because they somehow 'self-purify' by expelling impurities from their interior. According to this view, the same mechanisms that made it possible to grow very pure nanocrystals also made it extremely difficult to dope them. We have shown that doping difficulties are not intrinsic, and indeed are amenable to systematic optimization using straightforward methods from physical chemistry."
Future efforts will focus on incorporating impurities which are chosen for specific applications. For example, solar cells and lasers could benefit from impurities that add an additional electrical charge to the nanocrystal. In addition, impurities will be chosen to explore the use of nanocrystals in spin electronics (or "spintronics"). Spintronic devices utilize the fact that electrons not only possess charge, but also a quantum mechanical spin. The spin provides an additional degree of freedom that can be exploited in devices to realize a host of new spintronic technologies, from. nonvolatile "instant-on" computers to so-called "reconfigurable logic" elements whose underlying circuitry can be changed on-the-fly.
The research was conducted by Dr. Steven Erwin, Dr. Michael Haftel, and Dr. Alexander Efros from NRL's Materials Science and Technology Division; Dr. Thomas Kennedy from NRL's Electronics Science and Technology Division; and Ms. Lijun Zu and Professor David Norris from the Department of Chemical Engineering and Materials Science at the University of Minnesota. The Office of Naval Research and the National Science Foundation provided funding for the research.
About NRL:
NRL conducts a broadly-based multidisciplinary program of scientific research and advanced technological development directed toward maritime applications of new and improved materials, techniques, equipment, systems, and ocean, atmospheric, and space sciences and related technologies.
For more information, please visit www.nrl.navy.mil
Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Related News Press |
Possible Futures
Stability of perovskite solar cells reaches next milestone January 27th, 2023
Danish quantum physicists make nanoscopic advance of colossal significance January 27th, 2023
UC Irvine researchers decipher atomic-scale imperfections in lithium-ion batteries: Team used super high-resolution microscopy enhanced by deep machine learning January 27th, 2023
Spintronics
Linearly assembled Ag-Cu nanoclusters: Spin transfer and distance-dependent spin coupling November 4th, 2022
Spin photonics to move forward with new anapole probe November 4th, 2022
Novel nanowire fabrication technique paves way for next generation spintronics November 4th, 2022
“Kagome” metallic crystal adds new spin to electronics October 28th, 2022
Chip Technology
Manufacturing advances bring material back in vogue January 20th, 2023
Vertical electrochemical transistor pushes wearable electronics forward: Biomedical sensing is one application of efficient, low-cost transistors January 20th, 2023
Approaching the terahertz regime: Room temperature quantum magnets switch states trillions of times per second January 20th, 2023
Sensors
Development of bio-friendly transparent temperature sensor technology that precisely measures temperature changes by light January 6th, 2023
Discoveries
Stability of perovskite solar cells reaches next milestone January 27th, 2023
Qubits on strong stimulants: Researchers find ways to improve the storage time of quantum information in a spin rich material January 27th, 2023
Temperature-sensing building material changes color to save energy January 27th, 2023
Announcements
Temperature-sensing building material changes color to save energy January 27th, 2023
Energy
Stability of perovskite solar cells reaches next milestone January 27th, 2023
Temperature-sensing building material changes color to save energy January 27th, 2023
Polymer p-doping improves perovskite solar cell stability January 20th, 2023
![]() |
||
![]() |
||
The latest news from around the world, FREE | ||
![]() |
![]() |
||
Premium Products | ||
![]() |
||
Only the news you want to read!
Learn More |
||
![]() |
||
Full-service, expert consulting
Learn More |
||
![]() |