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15. Concluding remarks

Author

Bellmann, K., Hüttl, R. F., Hüttl, Reinhard F., editor, Schneider, Bernd Uwe, editor, and Bellmann, Klaus, editor

Published
1998
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25. Impact of GaN cap thickness on optical, electrical, and device properties in AlGaN/GaN high electron mobility transistor structures.

Author

Waltereit, P., Müller, S., Bellmann, K., Buchheim, C., Goldhahn, R., Köhler, K., Kirste, L., Baeumler, M., Dammann, M., Bronner, W., Quay, R., and Ambacher, O.

Subjects
WIDE gap semiconductors, ELECTRON mobility, GALLIUM nitride, HALL effect, MATHEMATICAL physics, SEMICONDUCTOR-metal boundaries
Abstract

We systematically investigate Al0.22Ga0.78N/GaN high electron mobility transistors with GaN cap layer thicknesses of 0, 1, and 3 nm. All samples have electron mobilities around 1700 cm2/Vs and sheet carrier concentrations around 8×1012 cm-2 as determined by Hall effect measurements. From photoreflectance measurements we conclude that the electric field strength within the AlGaN barrier increases with GaN cap layer thickness leading to a broadening of the transition peaks as determined by spectroscopic ellipsometry. The surface potential as determined by photoreflectance varies in the range between 0.585 and 0.249 eV dependent on the thickness of the GaN cap. Device results show a significant decrease in Ohmic contact resistance, an increase in ideality factor, a decrease in gate and drain leakage currents, an increase in gain, and an increase in power added efficiency with increasing cap layer thickness. Finally, devices with GaN cap show an improved direct current reliability compared to their counterparts without GaN cap. [ABSTRACT FROM AUTHOR]

Published
2009
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33. Book reviews

Author

Prauser, H., Hagemann, Horstmann, Chr., Bellmann, K., Meyer, M., Börner, Th., Lohs, Kh., and Rick, Charles M.

Published
1974
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37. Book reviews

Author

Hagemann, Scholz, G., Bellmann, K., Schwanitz, F., Künzel, G., K. A., Thiele, H., Wöhrmann, Däßler, H. -G., and Löther, Rolf

Published
1970
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45. Development of rugged 2 GHz power bars delivering more than 100 W and 60% power added efficiency

Author

Waltereit, P., Bronner, W., Quay, Rüdiger, Dammann, M., Müller, S., Mikulla, M., Ambacher, O., Harm, L., Lorenzini, M., Rödle, T., Riepe, K., Bellmann, K., Buchheim, C., Goldhahn, R., and Publica

Subjects
AlGaN/GaN, reliability, MOCVD, performance
Abstract

In this work we systematically study the structural, optical and electrical properties of AlGaN/GaN heterostructures grown by MOCVD 3-inch on SiC substrates Thefinally developed HEMTs demonstrate excellent highvoltage stability, high power performance and large power added efficiencies. For a drain bias of 100 V an output-power-density around 26 W/mm with 25 dB linear gain is obtained. On 36 mm gate width devices an output power beyond 100 W is achieved with a power added efficiency above 60% and a linear gain around 17 dB. Ruggedness on these large devices is proven by successfully passing harsh intentional device mismatch tests during operation at 50 V. Reliability is tested at a drain bias of 50 V. Under DC conditions a drain-current degradation below 20% after 20 years is extrapolated. Under RF stress the observed change in output power is well below 0.1 dB after a test duration of more than 500h.

Published
2010

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