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Laser spectroscopy eases nanoscale measurement

Posted: 06 Sep 2013 ?? ?Print Version ?Bookmark and Share

Keywords:nanoscale measurement? band offset? laser spectroscopy?

A team of researchers from Drexel University's College of Engineering has developed a procedure that according to them could ease the challenge of measuring key features of electron behaviour. This allows the design of ever-shrinking components that allow cell phones, laptops and tablets to get increasingly thinner and more energy efficient, the researchers noted.

"The interface between two semiconductor materials enables most of the electronic gadgets we use each day, from computers to mobile phones, displays and solar cells," said Guannan Chen, a graduate student in Drexel's Materials Science and Engineering department and the lead author of the group's report, which was recently published in Nano Letters. "One of the most important features of the interface is the height of the energy step required for the electron to climb over, known as band offset. Current methods for measuring this step height in planar devices are not practical for nanoscale devices, however, so we set off to find a better way to make this measurement."

Tracking a nanowire device's photocurrent responses, created by varying the wavelengths of a laser

Figure 1: Tracking a nanowire device's photocurrent responses, created by varying the wavelengths of a laser.

Measuring the band offset faced by electrons jumping from one material to another is a key component of the design process because it guides the redesign and prototyping of nanoscale components in order to make them as efficient and effective as possible.

Using laser-induced current in a nanowire device and its dependence on the wavelength of the laser, the team devised a new method to derive the band offset. As they continuously change the wavelength of the laser, they measure the photocurrent responses. From this data they are able to determine the band offset.

"Using the interface within a co-axial core-shell semiconductor nanowire as a model system, we made direct measurements of the band offset for the first time in nanowire electronics," Chen said. "This is a significant cornerstone to freely design new nanowire devices such as solar cells, LEDs, and high speed electronics for wireless communications. This work can also extend to broader material systems which can be tailored for specific application."

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