Lasers Leave a Mark on Materials - At the Atomic Level
Ultrafast laser shots act like dopants to create new electronic properties in materials.
The Science
One way to control the properties of electronic materials is to add small amounts of other elements, called dopants. An alternative to conventional dopants is shooting a material with a laser to change its electronic properties. This laser technique is based on one quadrillionth of a second, or a femtosecond, pulses. These pulses advantageously do not distort or strain the structure like the addition of conventional dopants. Also, coupling femtosecond laser treatment with electron-based ultrafast characterization allowed an in-depth assessment of these transformations.
The Impact
This laser-based technique could replace conventional methods to control electronic properties in semiconductors and could lead to the next generation of electronics.
Summary
Semiconductors can control electrical current in electronics because their conductivity can be manipulated transiently. The electronic properties of diodes and transistors depend on the nature of trace metallic impurities, called dopants, added into semiconductors. These dopants are strategically added into bulk silicon and germanium to achieve efficient solid-state electronics. Researchers developed a new method to dope semiconductor materials. Scientists shot femtosecond (<10-14 seconds) laser pulses at an unconventional semiconductor (tantalum disulfide) composed of alternating layers of metal and insulator. The phase changes caused by the laser pulses act like dopants in this new process called “photo-doping” to trigger changes in the electronic structures and properties. The ultrashort laser pulses temporarily weaken the glue at different bonding sites to set off chain reactions where new electronic phases can spontaneously form—a phenomenon known as “photo-induced phase transition.” A new ultrafast electron-based imaging technique allowed visualization of changes on femtosecond timescales of the electronic phases in these materials. Researchers identified metastable and hidden phases with very different properties that were intimately tied to subtle distortions in the atomic structures not seen by any other technique. Ultrafast “photo-doping” could lead to the development of next-generation electronic materials, and possibly switching devices composed of un-doped, unconventional semiconductors that can be controlled optically.
Contact
Chong-Yu Ruan
Michigan State University
[email protected]
Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences and Michigan State University Foundation Grant.
Publications
T.-R. T. Han, F. Zhou, C. D. Malliakas, P. M. Duxbury, S. Mahanti, M. G. Kanatzidis, and C. Y. Ruan, “Exploration of metastability and hidden phases in correlated electron crystals visualized by femtosecond optical doping and electron crystallography.” Science Advances 1, e1400173 (2015). [DOI: 10.1126/sciadv.1400173]
Related Links
EurekAlert (American Association for the Advancement of Science)
Michigan State University Article
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Performer: University , DOE Laboratory
