Francesca Danesin

Evidence of traps creation in GaN/AlGaN/GaN HEMTs after a 3000 hour on-state and off-state hot-electron stress

A long-term 3000-hour test under on-state conditions (VDS =25V, 6W/mm constant dissipated power) and off-state conditions (V DS=46V, VGS=-6V) on GaN/AlGaN/GaN HEMTs is presented. Trapping presence and hot-electrons effect are characterized by means of low-frequency techniques (low-frequency noise measurements, transconductance frequency dispersion, gate-lag). The on-state stress shows the most important degradation. Since our measurements point out to the creation of traps in the gate-to-drain surface region during the stress, this degradation is ascribed to the effect of hot-electrons

Mechanisms of RF Current Collapse in AlGaN–GaN High Electron Mobility Transistors

The physical mechanisms underlying RF current- collapse effects in AlGaN-GaN high-electron-mobility transistors are investigated by means of measurements and numerical device simulations. This paper suggests the following conditions: 1) both surface and buffer traps can contribute to RF current collapse through a similar physical mechanism involving capture and emission of electrons tunneling from the gate; 2) surface passivation strongly mitigates RF current collapse by reducing the surface electric field and inhibiting electron injection into traps; 3) for surface-trap densities lower than 9 x 1012 cm-2, surface-potential barriers in the 1-2-eV range can coexist with surface traps having much a shallower energy and, therefore, inducing RF current-collapse effects characterized by relatively short time constants.

A review of failure modes and mechanisms of GaN-based HEMTs

Failure modes and mechanisms of AlGaN/GaN HEMTs, observed during accelerated tests at various bias conditions are reviewed.

ESD robustness of AlGaN/GaN HEMT devices

We have investigated the robustness of GaN-HEMT devices submitted to ESD events in different configurations. A good scaling of the failure current with the device width has been observed for both drain and gate TLP stresses. We have identified two failure mechanisms, related to the gate-source diode degradation and drain to gate filaments formation. Filaments formation was identified by means of emission microscopy, both while applying DC bias and during the TLP measurement itself. We have also found that the traditional TLP leakage measurement can not be used as a valid failure criterion. On the contrary, the gate-source diode measurement can provide interesting information on the device life-state.

Characterization and analysis of trap-related effects in AlGaN-GaN HEMTs

Abstract Traps are characterized in AlGaN–GaN HEMTs by means of DLTS techniques and the associated charge/discharge behavior is interpreted with the aid of numerical device simulations. Under specific bias conditions, buffer traps can produce “false” surface-trap signals, i.e. the same type of current-mode DLTS (I-DLTS) or ICTS signals that are generally attributed to surface traps. Clarifying this aspect is important for both reliability testing and device optimization, as it can lead to erroneous identification of the degradation mechanism, thus resulting in wrong correction actions on the technological process.

False surface-trap signatures induced by buffer traps in AlGaN-GaN HEMTs

Buffer traps can induce “false” surface-trap signatures in AlGaN-GaN HEMTs, namely the same type of current-mode DLTS peaks and pulse responses that are generally attributed to surface traps. Device simulations are adopted to clarify the underlying physics. Being aware of the above phenomenon is important for both reliability testing and device optimization, as it can lead to erroneous identification of the degradation mechanism, thus resulting in inappropriate correction actions on the technological process.

Degradation Induced by 2-MeV Alpha Particles on AlGaN/GaN High Electron Mobility Transistors

Abstract We studied the degradation of AlGaN/GaN High Electron Mobility Transistors (HEMT) after 2-MeV alpha irradiation for two different fluences, namely 10 13 α /cm 2 and 10 14 α /cm 2 . After the exposure and depending on the irradiation fluence, we observed a drop both in drain current and transconductance, and a reduction in the leakage current of the gate diode. We attributed these effects to bulk damage, radiation-induced formation of deep-level trap sites in the channel layer, and doping compensation/removal in the barrier layer.

Electrical characterization and reliability study of HEMTs on composite substrates under high electric fields

Abstract The electrical characterization, in DC and pulsed regime, and reliability analysis of T-gate high electron mobility transistors built on SiCopSiC and SopSiC composite substrates under high electric fields are here presented. The impact of different gate–drain overhang lengths on the electrical behavior of SiCopSiC devices is also investigated. We will demonstrate that devices can be efficiently realized over the proposed composite substrates, and that performances and robustness are comparable to devices processed on SiC or sapphire. The sensitivity to ESD-like events is also reported, using emission microscope for the failure analysis investigation.

Reliability aspects of GaN-HEMTs on composite substrates

This paper shows electrical characterizations and reliability analysis performed on AlGaN/GaN HEMTs processed on epitaxial layers grown on composite substrates. The results are very promising for the fabrication of low cost high power microwave transistors for wireless communication systems. The composite substrates constitute a valuable alternative to the silicon since better thermal properties are expected.