Thin Photodetector Could Increase Performance Without Adding Bulk
July 10, 2017 | University of Wisconsin-MadisonEstimated reading time: 3 minutes
In today’s increasingly powerful electronics, tiny materials are a must as manufacturers seek to increase performance without adding bulk.
Smaller also is better for optoelectronic devices — like camera sensors or solar cells — which collect light and convert it to electrical energy. 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.
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 become almost transparent and actually lose some ability to gather or absorb light.
Now, in a nanoscale photodetector that combines a unique fabrication method and light-trapping structures, a team of engineers from the University of Wisconsin–Madison and the University at Buffalo has overcome both of those obstacles.
The researchers — electrical engineering professors Zhenqiang (Jack) Ma and Zongfu Yu at UW–Madison and Qiaoqiang Gan at UB — described their device, a single-crystalline germanium nano-membrane photodetector on a nano-cavity substrate, today (July 7, 2017) in the journal Science Advances.
“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 Ma.
The device consists of nano-cavities sandwiched between a top layer of ultrathin single-crystal germanium and a reflecting layer of silver.
Tuned to absorb specific light wavelengths, the new photodetector consists of nanocavities sandwiched between a ultrathin single-crystal germanium top layer and reflective silver on the bottom. ILLUSTRATION BY ZHENYANG XIA/UW-MADISON COLLEGE OF ENGINEERING
“Because of the nano-cavities, the photons are ‘recycled’ so light absorption is substantially increased — even in very thin layers of material,” says Ma.
Nano-cavities are made up of an orderly series of tiny, interconnected molecules that essentially reflect, or circulate, light. Gan already has shown that his nano-cavity structures increase the amount of light that thin semiconducting materials like germanium can absorb.
However, most germanium thin films begin as germanium in its amorphous form — meaning the material’s atomic arrangement lacks the regular, repeating order of a crystal. That also means its quality isn’t sufficient for increasingly smaller optoelectronics applications.
That’s where Ma’s expertise comes into play. A world expert in semiconductor nano-membrane devices, Ma used a revolutionary membrane-transfer technology that allows him to easily integrate single crystalline semiconducting materials onto a substrate.
Shrinking photodetectors like this scant wafer held in a frame for testing in the laboratory of UW–Madison engineering Professor Zhenqiang (Jack) Ma help make consumer electronics smaller. STEPHANIE PRECOURT/UW-MADISON COLLEGE OF ENGINEERING
The result is a very thin, yet very effective, light-absorbing photodetector — a building block for the future of optoelectronics.
“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 Yu, who conducted computational analysis of the detectors.
While the researchers demonstrated their advance using a germanium semiconductor, they also can apply their method to other semiconductors.
“And importantly, by tuning the nano-cavity, we can control what wavelength we actually absorb,” says Gan. “This will open the way to develop lots of different optoelectronic devices.”
The researchers are applying jointly for a patent on the technology through the Wisconsin Alumni Research Foundation. Other authors on the paper include Zhenyang Xia, Munho Kim, Ming Zhou, Tzu-Hsuan Chang, Dong Liu, Xin Yin, Kanglin Xiong, Hongyi Mi and Xudong Wang of UW–Madison; Haomin Song of the University at Buffalo; and Fengnian Xia of Yale University.
Suggested Items
Material Insight: The Dielectric Constant of PCB Materials
05/17/2024 | Dr. Preeya Kuray -- Column: Material InsightIn the world of PCB design, miniaturization can be achieved by using low dielectric constant (Dk) materials. Low Dk materials can allow for a reduction in thickness while maintaining a given trace width, leading to lower transmission loss and higher density circuitry.
IPC APEX EXPO: Some Thoughts About Growth
05/16/2024 | Dan Feinberg, I-Connect007After two and a half days of wandering the aisles at IPC APEX EXPO 2024, for the first time, I almost felt like I was exploring CES. There were so many booths and exhibits that I could describe, but I’d like to focus on the growth and huge value of this event, which has expanded well beyond just the growing and impressive exhibit show floor.
The Shaughnessy Report: Unlock Your High-speed Material Constraints
05/15/2024 | Andy Shaughnessy -- Column: The Shaughnessy ReportThe world of PCB materials used to be a fairly simple one. It was divided into two groups: the “traditional” laminates, often called FR-4, and the high-speed laminates developed especially for high-speed PCBs. These were two worlds that usually didn’t collide. But then traditional laminates started getting better, and high-speed designers and design engineers took notice and started to reconsider what FR-4 could be used for.
Breaking High-speed Material Constraints: Design007 Magazine — May 2024
05/14/2024 | I-Connect007 Editorial TeamDo you need specialty materials for your high-speed designs? Maybe not. Improvements in resins mean designers of high-speed boards can sometimes use traditional laminate systems instead of high-speed materials, saving time and money while streamlining the fab process. In the May 2024 issue of Design007 Magazine, our contributors explain how to avoid overconstraining your materials when working with high-speed boards.
Indium Experts to Present at Electronics in Harsh Environments SMTA Conference
05/13/2024 | Indium Corporationndium Corporation Technical Manager for Europe, Africa, and the Middle East, Karthik Vijay, will deliver a technical presentation and Indium Corporation Senior Technologist, Dr. Ronald Lasky, will deliver both a workshop and technical presentation at the Electronics in Harsh Environments SMTA Conference on May 14-16 in Copenhagen, Denmark.