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Efficiency leap in nanowire solar cells

Researchers at LTH have shown that efficient solar cells can be realized at great materials savings as compared to current technology. The researchers synthesized and characterized InP nanowire solar cells where the nanowires cover about 12 % of the surface, but still generates an amount of electricity nearly as much as what is produced by an InP thin-film cell. Light absorption in the nanowires is efficient beyond what can be explained in a ray optics picture, and relies on optical modes forming in the nanowires. Below, a few of the four million nanowires having 180 nm nm in diameter and 1.5 µm tall—in a 1-mm2 cell are pictured here from above and on angle. Though not yet efficient enough for commercialization, the device is readily scalable to wafer-sized cells by use of nanoimprint lithography and electroplating for defining Au patterns used for synthesis based on the vapor liquid solid growth mode. The cell efficiency was evaluated at the Fraunhofer institute for solar energy systems (J. Wallentin et al., Science, 339, 1057, doi:10.1126/science.1230969

III-V CMOS technology offers the combination of heterostructure design, gate-isolation, and complementary functionality. The figure shows a wavelet generator where a III-V MOSFET  is used as a switch. Coherent wavelets are obtained with sub-period oscillation starting time. L. Ohlsson, et al Monolithically-Integrated Millimetre-Wave Wavelet Transmitter with On-Chip Antenna IEEE Microwave and Wireless Components Letters 24, 625 (2014)

Advanced III-V CMOS technology for millimeter-wave devices

III-V CMOS are currently considered as one candidate to extend the CMOS scaling. Lund University has a strong effort in the field with a particular focus on millimeter-wave devices and applications. The researchers have been among the first to implement a gate-last process with epitaxially regrown contacts in both planar and vertical InGaAs nanowire geometry. Low defects levels have been measured electrically and the details in the chemical composition at the interface have been evaluated at MAX-lab. Small and efficient transmitters have been integrated on sub-wavelength antennas suitable for radar and communication.

Schematic illustration of nanowire growth by means of Aerotaxy. IN a continuous flow process, gold metal is vaporized and cooled to form an aerosol of nanoparticles, which is size selected with a differential mobility analyzer. The gold aerosol is mixed with trimethylgallium and arsine in the cylindrical Aerotaxy reactor, where rapid nanowire growth  occurs, yielding 2 µm long nanowires in 2 seconds. Downstream the reactor, wires are collected for further study or device integration. Image: Illustration by M. Heurlin, SEM by W. Metaferia. Reference: M. Heurlin, M. H. Magnusson, D. Lindgren, M. Ek, L. R. Wallenberg, K. Deppert, and L. Samuelson, “Continuous gas-phase synthesis of nanowires with tunable properties”, Nature 492 90 (2012)

Aerotaxy – a new way to make nanowires

Researchers at Lund University have developed a method for controlled mass production of semiconductor nanowire materials. The method, called Aerotaxy, is an up-scalable, continuous process, where aerosol seed particles are transformed into nanowires without the need of a substrate, proving that nanowire growth is a process primarily controlled by the seed particle. This continuous growth method is 20-1000 times faster than conventional epitaxy. The method allows nanowires to be produced in a cost-efficient way, with potential applications in solar cells, LEDs and batteries. The work is done in close collaboration between crystal growers and electron microscopists, where recent in situ TEM studies reveal details of nanowire nucleation and growth with atomic resolution.

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