Abstract
AbstractAlGaN/GaN HEMTs with a thin InGaN cap layer has been proposed to implement the normally‐off HEMTs. The key idea is to employ the polarization‐induced field in the InGaN cap layer, by which the conduction band is raised leading to the normally‐ off operation. Fabricated HEMT with an In0.2Ga0.8N cap layer with a thickness of 5 nm showed normally‐off operation with a threshold voltage of 0.4 V and a maximum transconductance of 85 mS/mm forthe device with a 1.9‐μm‐long gate. By etching‐off the In0.2Ga0.8N cap layer at the access region using gate electrode as an etching mask, the maximum transconductance has increased from 85 to 130 mS/mm due to a reduction of the parasitic source resistance. The transconductance was increased from 130 to 145 mS/mm by annealing the devices at 250 °C for 20 minutes in a N2 atmosphere. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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