TechBlog

Engineers and applied physicists from Harvard University have demonstrated the first room-temperature electrically-pumped semiconductor source of coherent Terahertz (THz) radiation, also known as T-rays. The breakthrough in laser technology, based upon commercially available nanotechnology, has the potential to become a standard Terahertz source to support applications ranging from security screening to chemical sensing.Spearheaded by research associate Mikhail Belkin and Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, both of Harvard’s School of Engineering and Applied Sciences (SEAS), the findings will be published in the May 19 issue of Applied Physics Letters. The researchers have also filed for U.S. patents covering the novel device.

Using lasers in the Terahertz spectral range, which covers wavelengths from 30 to 300å, has long presented a major hurdle to engineers. In particular, making electrically pumped room-temperature and thermoelectrically-cooled Terahertz semiconductor lasers has been a major challenge. These devices require cryogenic cooling, greatly limiting their use in everyday applications.

Continue reading ‘Engineers Demonstrate First Room-Temperature Semiconductor Source Of Coherent Terahertz Radiation’ »

In a significant breakthrough, researchers at Northwestern University’s Center for Quantum Devices (CQD) have demonstrated visible-blind avalanche photodiodes (APDs) capable of detecting single photons in the ultraviolet region (360-200 nm).

Previously, photomultiplier tubes (PMTs) were the only available technology in the short wavelength UV portion of the spectrum capable of single photon detection sensitivity. However, these fragile vacuum tube devices are expensive and bulky, hindering true systems miniaturization.

The Northwestern team, led by Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at Northwestern’s McCormick School of Engineering, became the world’s first to demonstrate back-illuminated single photon detection from a III-nitride photodetector. These back-illuminated devices, based on GaN compound semiconductors, benefit from the larger ionization coefficient for holes in this material. The back-illumination geometry will facilitate future integration of these devices with read-out circuitry to realize unique single-photon UV cameras. Towards that end, the team has already demonstrated excellent uniformity of the breakdown characteristics and gain across the wafer.

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Forty years ago, mathematician Mark Kac asked the theoretical question, “Can one hear the shape of a drum?”

If drums of different shapes always produce their own unique sound spectrum, then it should be possible to identify the shape of a specific drum merely by studying its spectrum, thus “hearing” the drum’s shape (a procedure analogous to spectroscopy, the way scientists detect the composition of a faraway star by studying its light spectrum).

But what if two drums of different shapes could emit exactly the same sound? If so, it would be impossible to work backward from the spectrum and uniquely surmise the physical structure of the drum, because there would be more than one correct answer to the question.

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Scientists have created silicon nanowires that are perfect—at least atomically. Down at the single-atom level, the identical wires have no bumps, bends, or other imperfections. They are perfectly crystalline, even more so than bulk silicon. The full array of nanowires is also highly parallel, and each wire is an excellent metallic conductor.

This research may be an important step forward for nanotechnology. Nanowires play a key role in developing nanoelectronics applications, and silicon nanowires are particularly important because of the central function that silicon plays in the semiconductor industry and current technologies. Some scientists believe that silicon nanowires will overtake carbon nanotubes in popularity, and they are being eyed for a variety of electronics applications and even quantum computing.

Therefore, the ability to create straight, identical, parallel, and atomically smooth nanowires could lead to new developments in nanoelectronics.