Laser pulses crystallize amorphous silicon, create nanostructured surface ideal for solar-cell applications
March 4, 2011 By Lee Swee Heng
Credit: iStockphoto.com/ason
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. Xincai Wang at the A*STAR Singapore Institute of Manufacturing Technology and co-workers 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 spectroscopya powerful technique for analyzing atomic structurewas 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.
More information: Wang, X.C. et al. Femtosecond laser induced surface nanostructuring and simultaneous crystallization of amorphous thin silicon film. Optics Express 18, 1937919385 (2010). http://dx.doi.org/ … OE.18.019379
Provided by Agency for Science, Technology and Research (A*STAR)
-
From lemons to lemonade: Reaction uses carbon dioxide to make carbon-based semiconductor,
32 comments
-
Thioridazine kills cancer stem cells in human while avoiding toxic side-effects of conventional cancer treatments,
3 comments
-
SpaceX private rocket blasts off for space station (Update),
42 comments
-
Climate scientists say they have solved riddle of rising sea,
30 comments
-
Research team claims to have found evidence Lake Cheko is impact crater for Tunguska Event,
18 comments
-
Question about induced E field.
1 hour ago
-
Charging a capacitor in a tesla coil
1 hour ago
-
Water Rocket
5 hours ago
-
why do trucks have bigger brakes?
9 hours ago
-
Solar Sail Physics - Do they work on a large scale?
10 hours ago
-
How should I switch an air conditioner off?
10 hours ago
- More from Physics Forums - General Physics
More news stories
Landmark calculation clears the way to answering how matter is formed
(Phys.org) -- An international collaboration of scientists, including Thomas Blum, associate professor of physics, is reporting in landmark detail the decay process of a subatomic particle called a kaon ...
May 25, 2012 |
4.4 / 5 (20) |
47
|
Is a classical electrodynamics law incompatible with special relativity?
(Phys.org) -- The laws of classical electromagnetism that were developed in the 19th century are the same laws that scientists use today. They include Maxwell’s four equations along with the Lorentz la ...
Lying in wait for WIMPs: Researchers seek to dramatically increase sensitivity of Large Underground Xenon detector
Although it's invisible, dark matter accounts for at least 80 percent of the matter in the universe. No one knows what it is, but most scientists would bet on weakly interacting massive particles, or WIMPs.
May 23, 2012 |
4 / 5 (7) |
15
|
Hall effect at the speed of light: How can you demonstrate relativistic effects with your mobile phone?
The relativistic Hall effect describing objects rotating at speeds comparable with the speed of light has been reported.
May 21, 2012 |
4.3 / 5 (3) |
8
Cloak of invisibility: Engineers use plasmonics to create an invisible photodetector
A team of engineers at Stanford and the University of Pennsylvania has for the first time used "plasmonic cloaking" to create a device that can see without being seen - an invisible machine that detects light. It is the first ...
May 21, 2012 |
4.8 / 5 (16) |
7
|
Scientist: Evolution debate will soon be history
(AP) -- Richard Leakey predicts skepticism over evolution will soon be history. Not that the avowed atheist has any doubts himself.
Dell tablet leak: 10.1-inch display, two-battery choice
(Phys.org) -- Headline after headline talks about vendors tablets in the wings as likely number-one contenders for the iPad. Such claims have justifiably been taken with a grain of salt, considering ...
SpotterRF debuts Radar Backpack Kit (w/ Video)
(Phys.org) -- SpotterRF has announced a special radar backpack kit designed to enhance situational awareness for soldiers on the ground. The company says its special radar is designed for warfighters as part ...
SpaceX capsule has 'new car' smell, astronauts say (Update)
SpaceX's Dragon cargo vessel smells like a new car, said astronauts at the International Space Station after opening the hatches Saturday following the spacecraft's landmark mission to the orbiting lab.
Thousands of shellfish found dead in Peru
Thousands of crustaceans were found dead off the coast of Lima following the mystery mass death of dolphins and pelicans, the Peruvian Navy said Friday.
Keep food safety in mind this memorial day weekend
(HealthDay) -- Picnics, parades and cookouts are as much a part of Memorial Day weekend as tributes to the United States' war veterans.
Mar 05, 2011
Rank: not rated yet