Research in Focus

GaN HFETs with high current and high breakdown voltage

For power conversion, which is used, for example, in electric cars and photovoltaic systems, transistors with low on-state resistance and high voltage stability are required. GaN HFETs offer a particularly high potential for such applications. In order to increase their breakdown voltage, Fe- or C-doped GaN buffers can be used. However, due to the higher barrier compared to undoped buffers, the carrier concentration within the channel decreases. The same applies for AlGaN buffers, which additionally increase the thermal resistance. This reduction of carrier concentration within the channel can be compensated by n-type doping of a thin (10 nm) AlGaN back barrier between C-doped buffer and channel layer. The electrons supplied from this layer result in a nearly doubled current Ids,max compared to an otherwise identical transistor structure. At the same time, voltage stability is not compromised and leakage currents remain low up to the measurement limit of 1000 V. Thus, such a thin n-doped AlGaN layer under the channel can significantly improve the trade-off between on-state resistance and breakdown voltage of GaN HFETs for power switching applications.

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780 nm modules for precision measurements in space

The Laser Metrology group at FBH develops micro-integrated laser modules specifically suited for precision measurements in space. Significant efforts are currently set on the development of laser modules for precision spectroscopy applications on board of a sounding rocket taking off in 2013. Medium-term perspective is to install these modules on board of the ISS or within a dedicated satellite mission. The laser module concept relies on micro integration of laser chips, optical components, and electronics. Mounting is carried out on a common AlN micro-bench so that volume and weight are reduced by a factor of a few 100 compared to commercially available systems. The laser modules feature an outstanding spectral short-term stability (few kHz linewidth) at a power level of 1 W and more. They have successfully passed mechanical vibration and shock tests required for space applications. All assembly technologies applied and components used are or can be space qualified. FBH currently develops a space-qualifiable packaging concept including fiber coupling on the micro-bench. Although this development addresses 780 nm, the concept can be easily transferred to other wavelengths from 650 nm to 1100 nm.


E. Luvsandamdin, G. Mura, A. Wicht, A. Sahm, G. Erbert and G. Tränkle "Hybrid-integrated ECDL for precision Rubidium spectroscopy in space" European Conf. on Lasers and Electro-Optics and the European Quantum Electronics Conf. (CLEO Europe - EQEC 2011), Munich, Germany, May 22-26, paper CB-P12-THU (2011).

E. Luvsandamdin, G. Mura, A. Wicht, A. Sahm, S. Spießberger, H. Wenzel, G. Erbert and G. Tränkle "Micro-integrated ECDLs for precision spectroscopy in space" Int. Conf. on Space Optical Systems and Applications (ICSOS 2011), Santa Monica, USA, May 11-13, pp. 383-385 (2011).

S. Spießberger, M. Schiemangk, A. Sahm, A. Wicht, H. Wenzel, J. Fricke, and G. Erbert
"1 W semiconductor based laser module with a narrow linewidth emitting near 1064 nm"
Proc. SPIE, vol. 7953, no. 795311 (2011).

Related article: "Bose-Einstein Condensation in Microgravity"

Line sensors for novel X-ray detectors

The FBH develops line sensors for innovative X-ray detectors in close cooperation with the Electronics Packaging Laboratory (IAVT) at TU Dresden. Only recently, novel direct-converting line detectors have been demonstrated. These devices resolve the disadvantages of present sensor systems comprising scintillator and photo detector. Key benefits are very low crosstalk between adjoining pixels, simple construction and expanded lifetime of the detector chips. Within the system, GaAs sensors directly convert X-ray photons into charge carriers with a lateral resolution of 100 µm per pixel. The demonstrator comprises a sensor with 1024 pixels and has been set up with assemblies for amplifier and evaluation electronics developed by the Fraunhofer institutes IZFP and IPMS.

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Oppermann, M.; Lohse, T.; Metasch, R.; Zerna, T.; Wolter, K.-J.
X-Ray Resistant Packaging for X-Ray Line Detectors. Paper and presentation on ESTC Berlin (2010).

Highly efficient power amplifiers and oscillators

In the framework of the regional growth core "Berlin WideBaSe", FBH and the regional SMEs BeMiTec, GloMic and Sentech joined forces to develop and market highly efficient microwave power amplifiers and oscillators. The focus is on technological concepts and circuit topologies towards highly efficient microwave amplifiers. Demonstrators are realized at two different frequencies. At 80 MHz, the desired power levels are 1 kW with 70% efficiency and accordingly 200 W with 60% efficiency at 2.45 GHz. These novel and highly efficient amplifiers will then be utilized for high-density plasma generation in plasma sources designed and fabricated by Sentech. Subsequently, the respective know-how gained during the project shall be marketed by the contributing companies. 

Berlin WideBaSe