| A team led by James Kolodzey produced electroluminescence in a combination of germanium and tin (GeSn), which may advance the development of mid-IR LEDs and lasers. (Image: UD) |
Newark, DE and Albany, NY--Researchers from the University of Delaware (UD) and the University at Albany-State University of New York (SUNY), led by UD researcher James Kolodzey, have demonstrated that it is possible to use a combination of germanium and tin (GeSn) to create LEDs that emit in the IR wavelength range around 2 μm.
The researchers doped the GeSn layers in a GeSn/Ge p-n heterostructure with boron; the GeSn layers took the crystal structure of the Ge substrate beneath. They observed electroluminescence in the structure with an emission peak at about 0.57 eV (2.17 μm) and a total integrated optical output of 54 μW at a peak current of 100 mA at a temperature of 100 K.
Until now, researchers were uncertain if GeSn was capable of efficient light emission. Kolodzey’s team, however, showed clear and efficient performance in the mid-IR -- a spectral region important for applications such as medical scanning and diagnostics, the remote sensing of biochemicals, communications and signaling, and security technology. “Our UD group is one of the few in the world working in this new field, and by using tin we have achieved an operating LED device with higher power output and longer wavelength operation than any previous reports or publications in this area,” says Kolodzey.
The Kolodzey research group first began growing GeSn samples in the lab using molecular beam epitaxy about three years ago. As they added increasing amounts of Sn, they noticed that the optical wavelengths became longer, the result of increasing the spacing between the atoms. “Specifically, we’ve shown that when tin concentrations in the alloy reach 6% to 7%, the light emitted from the alloy increases dramatically,” notes Kolodzey.
Health-care applications
The work may have health-care applications, Kolodzey says, particularly in the detection of skin cancer. “Germanium-tin alloys may provide a new diagnostic tool for illuminating skin tissue and detecting skin changes visible only in the infrared spectrum. It may also have dental applications,” he says.
Kolodzey says he hopes to develop a GeSn mid-IR laser that provides higher output power and a more easily controlled beam than an LED and that could be useful to develop new drugs and polymers, or for laser-surgery techniques.
The team published its findings in the journal Applied Physics Letters, volume 102 (25), p. 251117, 2013. Co-authors on the paper include UD graduate students Nupur Bhargava, Jay Prakash Gupta, and Sangcheol Kim, and Thomas Adam from SUNY. The research is funded in part by the Air Force Office of Scientific Research.
Source: http://www.udel.edu/udaily/2014/aug/optoelectronics-081313.html