In todays increasingly powerful electronics, tiny materials are a must as manufacturers seek to increase performance without adding bulk. Smaller is also better for optoelectronic deviceslike camera sensors or solar cellswhich collect light and convert it to electrical energy. <\/p>\n
This image shows the different layers of the nanoscale photodetector, including germanium (red) in between layers of gold or aluminum (yellow) and aluminum oxide (purple). The bottom layer is a silver substrate. (Credit: U. Buffalo) <\/p>\n<\/p>\n
(Click to enlarge) <\/p>\n
Think, for example, about reducing the size and weight of a series of solar panels, producing a higher-quality photo in low lighting conditions, or even transmitting data more quickly. <\/p>\n
However, two major challenges have stood in the way: First, shrinking the size of conventionally used amorphous thin-film materials also reduces their quality. And second, when ultrathin materials become too thin, they are almost transparentand actually lose some ability to gather or absorb light. <\/p>\n
The new nanoscale light detector, a single-crystalline germanium nanomembrane photodetector on a nanocavity substrate, could overcome both of these obstacles. Related:Russian Energy Minister: No Additional Output Cuts Are Needed <\/p>\n
Weve created an exceptionally small and extraordinarily powerful device that converts light into energy, says Qiaoqiang Gan, associate professor of electrical engineering in the University at Buffalos School of Engineering and Applied Sciences and one of the papers lead authors. The potential applications are exciting because it could be used to produce everything from more efficient solar panels to more powerful optical fibers. <\/p>\n
The idea, basically, is you want to use a very thin material to realize the same function of devices in which you need to use a very thick material, says Zhenqiang (Jack) Ma, professor in electrical and computer engineering at University of Wisconsin-Madison, also a lead author. <\/p>\n
Nanocavities are made up of an orderly series of tiny, interconnected molecules that essentially reflect, or circulate, light. <\/p>\n
The new device is an advancement of Gans work developing nanocavities that increase the amount of light that thin semiconducting materials like germanium can absorb. It consists of nanocavities sandwiched between a top layer of ultrathin single-crystal germanium and a bottom, reflecting layer of silver. <\/p>\n
Because of the nanocavities, the photons are recycled so light absorption is substantially increasedeven in very thin layers of material, says Ma. <\/p>\n
However, most germanium thin films begin as germanium in its amorphous formmeaning that the materials atomic arrangement lacks the regular, repeating order of a crystal. That also means that its quality isnt sufficient for increasingly smaller optoelectronics applications. <\/p>\n
An expert in semiconductor nanomembrane devices, Ma used a revolutionary membrane-transfer technology that allows him to easily integrate single crystalline semiconducting materials onto a substrate. <\/p>\n
The result is a very thin, yet very effective light-absorbing photodetectora building block for the future of optoelectronics. Related:Halliburton Sees Oil Price Spike By 2020 <\/p>\n
It is an enabling technology that allows you to look at a wide variety of optoelectronics that can go to even smaller footprints, smaller sizes, says Zongfu Yu, who conducted its computational analysis for the project. <\/p>\n
While the researchers demonstrated their advance using a germanium semiconductor, they can also apply their method to other semiconductors. And importantly, by tuning the nanocavity, we can control what wavelength we actually absorb, says Gan. This will open the way to develop lots of different optoelectronic devices. <\/p>\n
The researchers are applying jointly for a patent on the technology through the Wisconsin Alumni Research Foundation. <\/p>\n
A paper describing the research appears in the journalScience Advances.Additional coauthors of the paper are from the University at Buffalo, the University of Wisconsin-Madison, and Yale University. The National Science Foundation partially supported this research. <\/p>\n
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