Time-domain pulsed I-V measurements dedicated to characterising and modelling the time-dependent trapping phenomena of wide band-gap AlGaN/GaN high electron mobility transistors (HEMTs) are presented. The influence of temperature, electric field and their mutual interaction on trap activation and time constants are investigated and illustrated in the case of 2 × 75 × 0.15 µm 2 AlGaN/GaN HEMTs from the III-V Lab. These measurements show that the most influential parameter on trap activation is the electric field induced by the highest drain voltage V DS-max reached during a pulse sequence, which leads to the drain current collapse. These characterisations are intended to develop and improve new nonlinear models of GaN HEMTs, taking into account the dynamics of traps for modulated signals.Introduction: AlGaN/GaN high electron mobility transistors (HEMTs) are the most promising candidates for future wireless and radar applications. The intrinsic material properties of GaN such as high electron mobility, wide band-gap and high electron saturation velocity give it superiority over its predecessors like the Si and GaAs devices. Despite the fact that GaN technologies are already on the commercial market, mainly for applications below the X-band, many issues still need to be addressed. Among these, one of the most important issues is the drain current collapse also called kink effect that directly affects the output power, gain and RF transitions of microwave devices under pulse modulated signals.A similar behaviour was reported for GaAs devices [1] where it is caused by impact ionisation, which leads to a sudden rise in the drain current. This explanation is not well suited for GaN devices due to their high breakdown voltage although it can be true at very low temperatures [2]. Kink effect in GaN HEMTs is mainly attributed to carrier trapping [3]. In this Letter, a series of I-V measurements are performed under DC and pulsed modes to characterise the influence of the key parameters involved in carrier trapping, which are temperature and drain voltage.

Abstract-We propose here a non-linear GaN HEMT model for CAD including a trapping effects description consistent with both small-signal and large-signal operating modes. It takes into account the dynamics of the traps and then allows to accurately model the modulated large signal characteristics that are encountered in telecommunication and radar signals. This model is elaborated through low-frequency S-parameter measurements complementary to more classical pulsed-IV characterizations. A 8x75µm AlInN/GaN HEMT model was designed and particularly validated in large-signal pulsed RF operation. It is also shown that thermal and trapping effects have opposite effects on the output conductance, thus opening the way for separate characterizations of the two effects.

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This paper reports on the pulsed I-V and microwave characterizations of a Graphene Nano Ribbon FET (GNR-FET) for nonlinear electrical modeling. The extraction method of model parameters is based on the characterization of three specific technological structures called PAD, MUTE and FET (integrating only the coplanar access structure, the FET without graphene, and the entire GNR-FET) respectively. The differences between DC and pulsed I-V characterizations of the GNR FET and the evolution of its multi-bias S-parameters are investigated and compared to simulations. The nonlinear modeling of GNR FET is becoming of prime importance along with technological efforts to study the actual potential of this emerging technology.

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