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technology, Fraunhofer IAF cooperates, among others, with Robert Bosch GmbH in order to test the real-life behaviour of the devices. Stress tests conducted so far have not only shown the devices’ good performance, but gave also a first indication of high short-circuit strength.
“Validation of the devices developed within the project with a breakdown voltage of more than 600 V showed encouraging performance. Already in this early development stage, low conduction and switching losses comparable to considerably more mature and commercially available silicon carbide transistors were demonstrated during operation of the GaN devices in circuits ready for application. The stress tests conducted so far have also hinted at high short-circuit strength and thermal stability,” confirms Walter Daves, who supervised the project at Robert Bosch GmbH. The devices reached maximum currents of up to 100 A during on-resistance operation.
The transistors have already been tested for applications in battery chargers for electric cars, and, together with KACO new energy GmbH, also in photovoltaic inverters. The following partners also cooperate with Fraunhofer IAF in this research project, IXYS Semiconductor GmbH, United Monolithic Semiconductors GmbH, Universität Erlangen-Nürnberg, RWTH Aachen.
New opportunities for GaN technology
Whereas silicon-based devices are slowly reaching their physical limits, gallium nitride technology offers new opportunities for power electronics. Gallium nitride devices can be operated under higher voltages and temperatures than conventional power devices based on silicon.
This allows a reduction of the cooling efforts; compact, light-weight and cost-effective voltage converters become possible. In comparison with silicon transistors, gallium nitride allows to increase the switching frequency by at least a factor of three.
Due to the higher breakdown strength and power density of the material, the devices are considerably more efficient than their silicon equivalent. This will reduce the energy consumed in order to charge the battery of an electric car or to feed in energy from solar parks into the grid.
“Besides using GaN transistors in electromobility and photovoltaics, they will also be able to increase efficiency and save energy in household applications, production technology or in generators for plasma and laser systems. Our continuous goal will be to increase reliability, thermal stability and switching frequency in order to use the full potential offered by gallium nitride technology,” explains Patrick Waltereit, project leader at
Fraunhofer IAF.
Gadolinium doped UV LEDs could enable portable low cost devices
The doped wires enable LED tuning at precise frequencies for commercial applications
Commercial uses for ultraviolet (UV) light are growing, and now a new kind of LED under development at Ohio State University could lead to more portable and low-cost uses of the technology.
The patent-pending LED creates a more precise wavelength of UV light than today’s commercially available UV LEDs, and runs at much lower voltages and is more compact than other experimental methods for creating precise wavelength UV light.
The LED could lend itself to applications for chemical detection, disinfection, and UV curing. With significant further development, it might someday be able to provide a source for UV lasers for eye surgery and computer chip manufacture.
In the journal Applied Physics Letters, Ohio State engineers describe how they created LEDs out of semiconductor nanowires which were doped with the rare earth element gadolinium.
The unique design enabled the engineers to excite the rare earth metal by passing electricity through the nanowires, says study co-author Roberto Myers, associate professor of materials science and engineering at Ohio State.
But his team didn’t set out to make a UV LED.
“As far as we know, nobody had ever driven electrons through gadolinium inside an LED before,” Myers says. “We just wanted to see what would happen.”
When doctoral students Thomas Kent and Santino Carnevale started creating gadolinium-containing LEDs in the lab, they utilised another patent-pending technology they had helped develop - one for creating nanowire LEDs. On a silicon wafer, they tailor the wires’ composition to tune the polarisation of the wires and the wavelength, or colour, of the light emitted by the LED.
Gadolinium was chosen not to make a good UV LED, but to carry out a simple experiment probing the basic properties of a new material they were studying, called gadolinium nitride. During the course of that original
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