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241 80 23 252, Fax: þ49 241 80 22 495We report on the fabrication and characterization of AlGaN/ GaN metal-insulator-semiconductor heterostructure field effect transistors (MISHFETs) using HfO 2 and Al 2 O 3 as gate dielectric, deposited by atomic layer deposition (ALD). Improved device performance has been observed for all MISHFET devices as compared to the reference HFET. The additional dielectric layer underneath the gate metallization leads to a significant decrease of gate leakage currents and thus prevents device degradation and losses. Furthermore, the 2DEG sheet carrier concentration increases depending on the k-value of the oxide as well as the oxide thickness. The thin (3-9 nm) dielectric layer is serving simultaneously as surface passivation, mitigating dc-to-rf dispersion. However, less has been reported about the impact of gate insulator thickness on the electrical performance, in particular in terms of dc-to-rf dispersion. In this paper, full recovery of dc drain current is demonstrated with a MISHFET with 9 nm Al 2 O 3 oxide thickness.

We report on the fabrication of AlGaN/GaN MISHFETs using SiO2 and SiN as gate dielectrics. In particular, two different passivation procedures are investigated with respect to the resulting electrical properties. A fluorine based ICP etch step, as used here to remove the gate dielectric prior to passivation layer deposition, is shown to deteriorate the sheet carrier concentration and mobility. Depositing the passivation layer upon the gate dielectric, on the other hand, slightly decreases the sheet resistance as compared to a conventional HFET. Gate diode characteristics reveal significant reduction of gate leakage currents in both, reverse and forward biasing regions, of 1‐2 and up to 6 orders of magnitude, respectively. All devices exhibit more pronounced current collapse compared to a conventional passivated HFET. In addition, a clear depencency on the processing scheme is observed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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GaN HFETs and MISHFETs are promising power devices for RF and microwave power applications. However, the performance of devices can be compromised under some operating conditions. From the device development point of view, device optimization is necessary to obtain the best possible performance. For device modeling and design purposes, the device needs to be characterized and modeled accurately in order to foresee how the device will behave under realistic operating conditions.In this paper, an improved EEHEMT1-based model for GaN MISHFETs, will be introduced. This model is capable of describing the knee region of the device's output characteristics, dispersion effects as well as gate diode behavior accurately. The models will be incorporated in a switched-mode amplifier topology and evaluations will be made to determine the suitability of MISHFETs in these amplifiers.