Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Laser physics: Getting silicon into order

04.03.2011
Short pulses of laser light can crystallize amorphous silicon and create a nanostructured surface texture ideal for solar-cell applications

The importance of silicon for almost every element in modern-day electronic devices and computers is due largely to its crystalline atomic structure. Crystalline silicon, however, is much more expensive to produce than its non-crystalline or amorphous form, which has limited the cost reduction achievable in devices such as silicon-based solar cells.


Copyright : iStockphoto.com/ason

Xincai Wang at the A*STAR Singapore Institute of Manufacturing Technology and co-workers[1] have now shown that ultrafast pulses of light can be used to crystallize amorphous silicon and to texture its surface.

The useful electronic properties of silicon stem from the way the atoms are arranged into a regular and repeating lattice. Amorphous silicon, on the other hand, does not display this long-range order: nearby atoms are bonded in the same way but the structure is not homogenous through the whole material. While lacking the extraordinarily useful properties of its crystalline relative, amorphous silicon does have some advantages. Thin films of amorphous silicon can be grown at low temperatures and therefore at much lower cost. In fact, amorphous silicon is used widely in the field of photovoltaics for the conversion of sunlight into electrical power. But modifying the material could improve both electrical efficiency and optical sensitivity.

The researchers used laser radiation to achieve this level of material control. They focused pulses of light just 150 femtoseconds in duration into a spot 30 micrometers in diameter. This spot was then scanned across an 80-nanometer-thick layer of amorphous silicon deposited on a glass substrate.

The first noticeable effect was a change in color: the treated area was darker than the untreated region. Closer inspection using an electron microscope revealed that the laser created ‘nano-spikes’ in the silicon. This texturing is useful for photovoltaic applications because it reduces light reflection from the surface and thereby increases absorption: an effect the researchers confirmed directly.

Raman spectroscopy—a powerful technique for analyzing atomic structure—was then used to compare treated and untreated samples. The Raman spectrum for the untreated region had two peaks characteristic of an amorphous structure. But that of the treated sample displayed a third sharper peak indicative of a crystalline atomic structure. This state change was likely caused by the excitation of electrons at the surface of the silicon by the laser pulses, which weakened the interatomic bonds in a way fundamentally different from simple thermal melting.

“Our process has potential applications in the fabrication of high-efficiency thin-film silicon for solar cells, as well as thin-film transistors and other novel optoelectronic devices,” says Wang.

The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology

Journal information

[1] Wang, X.C. et al. Femtosecond laser induced surface nanostructuring and simultaneous crystallization of amorphous thin silicon film. Optics Express 18, 19379–19385 (2010).

Lee Swee Heng | Research asia research news
Further information:
http://www.research.a-star.edu.sg/research/6285
http://www.researchsea.com

More articles from Physics and Astronomy:

nachricht SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>