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Analysis of carbon doped GaN (GaN:C) layers in a wide temperature range reveals the same non-Arrhenius thermal behavior of capacitance transients related to trapping/detrapping dynamics on carbon defects and of the leakage current. Our results indicate that GaN:C does not behave like a classical semiconductor but is rather determined by a defect band (DB). Leakage via DB is the slowest process in charging/discharging dynamics, thus controlling it. We propose a microscopic model of carrier exchange between the carbon atom and the DB which can also explain the wide range of activation energies attributed previously to carbon. Understanding of leakage mechanisms and its interplay with charging is an important step towards optimization of GaN HEMT buffers.

Charge trapping in gallium-nitride (GaN) metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) is a serious reliability challenge but is still poorly understood. A promising opportunity to investigate physical defect properties has become available through nanoscale GaN fin-MIS-HEMTs which are small enough to be sensitive to the impact of individual defects. In this work, we extract the properties of four pre-existing single defects, which are identified by their correlated random telegraph noise (RTN) signals and step heights. We use a two-state non-radiative multi-phonon (NMP) model to extract their vertical positions, their trap levels and their apparent activation energies. We show that they are in close proximity to each other within the barrier layer and also share a similar trap-level despite their different capture and emission times. Furthermore, TCAD simulations are used to estimate the influence of the vertical and horizontal positions of single-traps which are in reasonable agreement with the experimental data.

We report on AlGaN/GaN MIS-HEMTs with a thermally stable dielectric/AlGaN interface induced by plasma fluorination. The plasma treatment leads to a modification of the "native" surface donors and a fundamentally different device and defect behavior. The feasibility of III-N surface defect modifications shows a new direction for reducing VTh drifts or the possibility of engineering the surface defects.

Charge trapping in the insulating layer of gallium-nitride (GaN) metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) is a serious reliability challenge but is still poorly understood. We demonstrate here that the observed Vth drift and recovery can be understood as charge capture and emission following a non-radiative multi-phonon (NMP) mechanism into traps with widely distributed properties. Furthermore, due to the large amount of trapped charge, the feedback of that charge on the surface potential and thus on the capture and emission times has to be considered self-consistently in order to correctly explain the temporal changes in their distributions.

Charge trapping phenomena at interfaces of GaN-based semiconductors with a dielectric are one of the major concerns in modern MIS-HEMT technologies. Fundamental questions about the nature and the behavior of interface defects must still be answered. We address these questions by investigating devices with and without an AlGaN layer at the the interface with the dielectric, using MIS capacitor test structures. We consider different methodologies to perform and analyze impedance measurements and the results are compared and discussed. Special attention is paid to the uncertainties and limitations inherent to different techniques, as well as the challenges due to the composite structure of GaN/AlGaN devices. We introduce an on the fly technique which allows the extraction of the device drift during stress. This enables us to suggest a lower and upper boundary for the amount of device degradation. The experimental results indicate the presence of similar defects at GaN and AlGaN surfaces, which therefore appear to be intrinsic to the III-N material.

Threshold voltage instabilities are investigated in GaN-based metal-insulator-semiconductor (MIS) high-electron-mobility-transistors (HEMTs) with specially designed on-wafer heaters structures. The heaters are based on metal lines or 2-dimensional electron gas (2DEG) resistors and enable to choose the temperature during stress and recovery in the stress-recovery experiments independently. It allows to decouple thermal activation of capture (< 0.9 eV) and emission (0.4–0.9 eV) processes at the dielectric/nitride interface, which is not possible in stress-recovery experiments performed at a common ambient temperature.

An unexpected enhancement of V th drift (ΔV th ) in GaN MIS-HEMTs induced by repetitive forward gate bias stress pulses in contrast to single pulses is found. Further, it is revealed that the slope of ΔV th recovery curves decreases for increasing intermediate-recovery time t i , i.e. the recovery time in between individual stress pulses. The observed behavior is explained by the interaction of the 2DEG channel with the dielectric/III-N interface via the III-N barrier during (repetitive) stress, for which a charge feedback mechanism plays a crucial role.

GaN-power HEMTs with insulated gate structure suffer from threshold voltage drifts (ΔV th ) under forward gate bias stress. We present a systematical approach to characterize the phenomenon and understand the dominant physical mechanisms causing this effect. We found out that ΔV th is caused by traps with a broad distribution of trapping and emission time constants. This distribution is analyzed using so called Capture Emission Time (CET) maps known from the study of bias temperature instability (BTI) in CMOS devices. Physical models, which could explain the broad distribution of time constants, are discussed.