路漫漫其修远兮分享 http://blog.sciencenet.cn/u/zhpd55 追求科学,勇于探索,苦海无涯,愿作小舟。

博文

究人员测量了低成本半导体近乎完美的性能

已有 2702 次阅读 2019-3-17 09:29 |个人分类:新科技|系统分类:博客资讯| 量子点, 半导体, 斯坦福大学

研究人员测量了低成本半导体近乎完美的性能

诸平
斯坦福大学(Stanford University)2019年3月15日提供的信息,该大学的研究人员开发出一种测量技术,测量了低成本半导体近乎完美的性能。
在太阳能电池板、相机传感器和医学成像工具中发现的先进电子产品中,被称为量子点的微小、易于生产的粒子,很可能很快就会取代更昂贵的单晶半导体。尽管量子点已经开始以量子点电视的形式进入消费市场,但长期以来,量子点电视的质量一直存在不确定性,阻碍了其发展。现在,斯坦福大学的研究人员开发的一种新的测量技术可能最终会消除这些疑虑。
斯坦福大学化学研究生戴维·哈尼菲(David Hanifi)说:“传统半导体是单晶,在真空中特殊条件下生长。我们可以在实验室里的烧瓶中大量制造量子点,我们已经证明它们和最好的单晶一样好。”
研究人员专注于量子点如何有效地重新发射它们所吸收的光,这是衡量半导体质量的一个指标。虽然之前对量子点效率的研究暗示了量子点的高性能,但这是第一个自信地证明量子点可以与单晶竞争的测量方法。这项研究是美国斯坦福大学
(Stanford University)、劳伦斯·伯克利国家实验室(Lawrence Berkeley National Laboratory)、加州大学伯克利分校(University of California, Berkeley), 日本有关公司(High Performance Materials Company, JXTG Nippon Oil & Energy Corporation)、比利时哈瑟尔特大学(Hasselt University)、荷兰埃因霍温理工大学(Eindhoven University of Technology)以及美国的卡佛利能源纳米科学研究所(Kavli Energy NanoScience Institute)合作完成的,相关研究结果,2019年3月15日已经在《科学》(Science)杂志网站发表——David A. Hanifi, Noah D. Bronstein, Brent A. Koscher, Zach Nett, Joseph K. Swabeck, Kaori Takano, Adam M. Schwartzberg, Lorenzo Maserati, Koen Vandewal, Yoeri van de Burgt, Alberto Salleo, A. Paul Alivisatos. Redefining near-unity luminescence in quantum dots with photothermal threshold quantum yield. Science,  15 Mar 2019: Vol. 363, Issue 6432, pp. 1199-1202. DOI: 10.1126/science.aat3803
加州大学伯克利分校的纳米科学和纳米技术的三星特聘教授,量子点的先驱研究者 Paul Alivisatos,也是论文的通讯作者,他强调了此测量技术如何能够引领新技术和新材料的发展,而这些新技术和新材料要求我们在很大程度上了解半导体的效率。
“这些材料的效率如此之高,以至于现有的测量无法量化它们到底有多好。这是一个巨大的飞跃。“也许有一天,它可以应用于需要发光效率远高于99%的材料的应用,而这些材料中的大多数还没有被发明出来。”更多信息敬请注意浏览原文或者相关报道

Between 99 and 100

Being able to forego the need for pricey fabrication equipment isn't the only advantage of quantum dots. Even prior to this work, there were signs that quantum dots could approach or surpass the performance of some of the best crystals. They are also highly customizable. Changing their size changes the wavelength of light they emit, a useful feature for color-based applications such as tagging biological samples, TVs or computer monitors.                                       Despite these positive qualities, the small size of quantum dots means that it may take billions of them to do the work of one large, perfect single crystal. Making so many of these quantum dots means more chances for something to grow incorrectly, more chances for a defect that can hamper performance. Techniques that measure the quality of other semiconductors previously suggested quantum dots emit over 99 percent of the light they absorb but that was not enough to answer questions about their potential for defects. To do this, the researchers needed a measurement technique better suited to precisely evaluating these particles.

"We want to measure emission efficiencies in the realm of 99.9 to 99.999 percent because, if semiconductors are able to reemit as light every photon they absorb, you can do really fun science and make devices that haven't existed before," said Hanifi.

The researchers' technique involved checking for excess heat produced by energized quantum dots, rather than only assessing light emission because excess heat is a signature of inefficient emission. This technique, commonly used for other materials, had never been applied to measure quantum dots in this way and it was 100 times more precise than what others have used in the past. They found that groups of quantum dots reliably emitted about 99.6 percent of the light they absorbed (with a potential error of 0.2 percent in either direction), which is comparable to the best single-crystal emissions.

"It was surprising that a film with many potential defects is as good as the most perfect semiconductor you can make," said Salleo, who is co-author of the paper.

Contrary to concerns, the results suggest that the quantum dots are strikingly defect-tolerant. The measurement technique is also the first to firmly resolve how different quantum dot structures compare to each other—quantum dots with precisely eight atomic layers of a special coating material emitted light the fastest, an indicator of superior quality. The shape of those dots should guide the design for new light-emitting materials, said Alivisatos.

Entirely new technologies

This research is part of a collection of projects within a Department of Energy-funded Energy Frontier Research Center, called Photonics at Thermodynamic Limits. Led by Jennifer Dionne, associate professor of materials science and engineering at Stanford, the center's goal is to create optical materials—materials that affect the flow of light—with the highest possible efficiencies.

A next step in this project is developing even more precise measurements. If the researchers can determine that these materials reach efficiencies at or above 99.999 percent, that opens up the possibility for technologies we've never seen before. These could include new glowing dyes to enhance our ability to look at biology at the atomic scale, luminescent cooling and luminescent solar concentrators, which allow a relatively small set of solar cells to take in energy from a large area of solar radiation. All this being said, the measurements they've already established are a milestone of their own, likely to encourage a more immediate boost in quantum dot research and applications.

"People working on these quantum dot materials have thought for more than a decade that dots could be as efficient as single crystal materials," said Hanifi," and now we finally have proof."

Superefficient light emission

A challenge to improving synthesis methods for superefficient light-emitting semiconductor nanoparticles is that current analytical methods cannot measure efficiencies above 99%. Hanifi et al. used photothermal deflection spectroscopy to measure very small nonradiative decay components in quantum dot photoluminescence. The method allowed them to tune the synthesis of CdSe/CdS quantum dots so that the external luminescent efficiencies exceeded 99.5%. This is important for applications that require an absolute minimum amount of photon energy to be lost as heat, such as photovoltaic luminescent concentrators.

Science, this issue p. 1199

Abstract

A variety of optical applications rely on the absorption and reemission of light. The quantum yield of this process often plays an essential role. When the quantum yield deviates from unity by significantly less than 1%, applications such as luminescent concentrators and optical refrigerators become possible. To evaluate such high performance, we develop a measurement technique for luminescence efficiency with sufficient accuracy below one part per thousand. Photothermal threshold quantum yield is based on the quantization of light to minimize overall measurement uncertainty. This technique is used to guide a procedure capable of making ensembles of near-unity emitting cadmium selenide/cadmium sulfide (CdSe/CdS) core-shell quantum dots. We obtain a photothermal threshold quantum yield luminescence efficiency of 99.6 ± 0.2%, indicating nearly complete suppression of nonradiative decay channels.




https://blog.sciencenet.cn/blog-212210-1168019.html

上一篇:手机背后的故事
下一篇:PNAS:美中研究人员合作从海水中制造氢燃料
收藏 IP: 72.51.164.*| 热度|

1 强涛

该博文允许注册用户评论 请点击登录 评论 (0 个评论)

数据加载中...
扫一扫,分享此博文

Archiver|手机版|科学网 ( 京ICP备07017567号-12 )

GMT+8, 2024-3-19 13:08

Powered by ScienceNet.cn

Copyright © 2007- 中国科学报社

返回顶部