A new slant on semiconductor characterization

November 05, 2015

From laptops and televisions to smartphones and tablets, semiconductors have made advanced electronics possible. These types of devices are so pervasive, in fact, that Northwestern Engineering's Matthew Grayson says we are living in the "Semiconductor Age."

"You have all these great applications like computer chips, lasers, and camera imagers," said Grayson, associate professor of electrical engineering and computer science in Northwestern's McCormick School of Engineering. "There are so many applications for semiconductor materials, so it's important that we can characterize these materials carefully and accurately. Non-uniform semiconductors lead to computer chips that fail, lasers that burn out, and imagers with dark spots."

Grayson's research team has created a new mathematical method that has made semiconductor characterization more efficient, more precise, and simpler. By flipping the magnetic field and repeating one measurement, the method can quantify whether or not electrical conductivity is uniform across the entire material - a quality required for high-performance semiconductors.

"Up until now, everyone would take separate pieces of the material, measure each piece, and compare differences to quantify non-uniformity," Grayson said. "That means you need more time to make several different measurements and extra material dedicated for diagnostics. We have figured out how to measure a single piece of material in a magnetic field while flipping the polarity to deduce the average variation in the density of electrons across the sample."

Remarkably, the contacts at the edge of the sample reveal information about the variations happening throughout the body of the sample.

Supported by funding from the Air Force's Office of Scientific Research, Grayson's research was published on October 28 online in the journal Physical Review Letters. Graduate student Wang Zhou is first author of the paper.

One reason semiconductors have so many applications is because researchers and manufacturers can control their properties. By adding impurities to the material, researchers can modulate the semiconductor's electrical properties. The trick is making sure that the material is uniformly modulated so that every part of the material performs equally well. Grayson's technique allows researchers and manufacturers to directly quantify such non-uniformities.

"When people see non-uniform behavior, sometimes they just throw out the material to find a better piece," Grayson said. "With our information, you can find a piece of the material that's more uniform and can still be used. Or you can use the information to figure out how to balance out the next sample."

Grayson's method can be applied to samples as large as a 12-inch wafer or as small as an exfoliated 10-micron flake, allowing researchers to profile the subtleties in a wide range of semiconductor samples. The method is especially useful for 2-D materials, such as graphene, which are too small for researchers to make several measurements across the surface.

Grayson has filed a patent on the method, and he hopes the new technique will find use in academic laboratories and industry.

"There are companies that mass produce semiconductors and need to know if the material is uniform before they start making individual computer chips," Grayson said. "Our method will give them better feedback during sample preparation. We believe this is a fundamental breakthrough with broad impact."
-end-


Northwestern University

Related Magnetic Field Articles from Brightsurf:

Investigating optical activity under an external magnetic field
A new study published in EPJ B by Chengping Yin, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Magnetic field with the edge!
This study overturns a dominant six-decade old notion that the giant magnetic field in a high intensity laser produced plasma evolves from the nanometre scale.

Global magnetic field of the solar corona measured for the first time
An international team led by Professor Tian Hui from Peking University has recently measured the global magnetic field of the solar corona for the first time.

Magnetic field of a spiral galaxy
A new image from the VLA dramatically reveals the extended magnetic field of a spiral galaxy seen edge-on from Earth.

How does Earth sustain its magnetic field?
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles.

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.

Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.

Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.

Read More: Magnetic Field News and Magnetic Field Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.