Laser Emission Study Initiates New Development Of Energy-Saving Devices For Future Generations

First Posted: Oct 23, 2015 10:44 AM EDT

Researchers have created a breakthrough development for the next generation's energy-saving power devices and solar cells, according to a news release.

This breakthrough study will be geared toward the development of a new evaluation method of semiconductors by using terahertz (THz) waves. The terahertz range refers to electromagnetic waves with frequencies between 100 GHz (clock frequency) and 10 THz. Terahertz waves can pass through a variety of amorphous substances, such as synthetics and textiles.  

Wide-gap semiconductors, such as gallium nitride (GaN), are commonly used for optical devices like blue-light emitting diodes (LED) since in the 1990s.

GaN is a very hard, mechanically stable wide bandgap semiconductor material that has very high heat capacity and thermal conductivity. They are also classified as materials for next-generation energy saving power devices, according to researchers. The only setback is that the quality of GaN crystals does not match conventional semiconductor materials like silicon (Si), and this prevents GaN from being used for power devices.

As a result, technology for producing high quality crystals with less defects and rearrangements was expected, along with the development of a new evaluation technology. This motivated a team of researchers to create a new development.

A team of researchers led by Iwao Kawayama, an associate professor of the Institute of Laser Engineering at Osaka University, were successful in identifying changes in defect density on the surface of GaN through the laser terahertz emission microscope (LTEM), which measures THz waves generated by laser emission.

The findings showed that the LTEM is valuable as a new method for evaluating the quality of wide-gap semiconductors, and could be a breakthrough in the development of next-generation optical devices, super high frequency devices and energy devices, according to the researchers.

The researchers examined the intensity distribution of THz generated by radiating ultraviolet femtosecond laser pulses on the surface of GaN crystal through the LTEM. The researchers found that there were regions with high intensity of THz emission and others with low intensity of THz emission.

When they compared the LTEM image with the image obtained through photo luminescence (PL) using a conventional method, there was a strong correlation between the distribution of emission intensity due to lattice defects, and the intensity distribution of THz wave emission, according to the researchers.

Results from measurement through the modification of excited lasers confirmed that THz emission needs excitation light with larger energy than the band gap energy, according to the researchers.

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