Gate stability of GaN-Based HEMTs with P-Type Gate

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Impact of the substrate and buffer design on the performance of GaN on Si power HEMTs

Abstract This paper presents an extensive analysis of the impact of substrate and buffer properties on the performance and breakdown voltage of E-mode power HEMTs. We investigated the impact of buffer thickness, substrate resistivity and substrate miscut angle, by characterizing several wafers by means of DC and pulsed measurement. The results demonstrate that: (i) the resistivity of the silicon substrate strongly impacts on the breakdown voltage and vertical leakage current. In fact, highly resistive substrates may partly deplete under high vertical bias, thus limiting the total potential drop on the epitaxial layers. As a consequence, the vertical I V plots show a "plateau", that limits the vertical leakage. (ii) the depletion of the substrate may worsen the dynamic performance of the devices, due to an enhancement of buffer trapping. (iii) Larger buffer thickness results in an increased robustness of the vertical stack, due to the thicker insulating region. (iv) the miscut angle (0°, 0.5°, and 1°) can significantly impact on both threshold voltage and the 2DEG density; devices with miscut substrate have higher current density. On the other hand, the dynamic on-resistance variation is comparable in the three cases

Analysis of threshold voltage instabilities in semi-vertical GaN-on-Si FETs

We present a first study of threshold voltage instabilities of semi-vertical GaN-on-Si trench-MOSFETs, based on double pulsed, threshold voltage transient, and UV-Assisted C-V analysis. Under positive gate stress, small negative V th shifts (low stress) and a positive V thshifts (high stress) are observed, ascribed to trapping within the insulator and at the metal/insulator interface. Trapping effects are eliminated through exposure to UV light; wavelength-dependent analysis extracts the threshold de-Trapping energy ≈2.95 eV. UV-Assisted CV measurements describe the distribution of states at the GaN/Al2O3 interface. The described methodology provides an understanding and assessment of trapping mechanisms in vertical GaN transistors

Exploration of Gate Trench Module for Vertical GaN devices

The aim of this work is to present the optimization of the gate trench module for use in vertical GaN devices in terms of cleaning process of the etched surface of the gate trench, thickness of gate dielectric and magnesium concentration of the p-GaN layer. The analysis was carried out by comparing the main DC parameters of devices that differ in surface cleaning process of the gate trench, gate dielectric thickness, and body layer doping. . On the basis of experimental results, we report that: (i) a good cleaning process of the etched GaN surface of the gate trench is a key factor to enhance the device performance, (ii) a gate dielectric >35-nm SiO2 results in a narrow distribution for DC characteristics, (iii) lowering the p-doping in the body layer improves the ON-resistance (RON). Gate capacitance measurements are performed to further confirm the results. Hypotheses on dielectric trapping/detrapping mechanisms under positive and negative gate bias are reported.Comment: 5 pages, 10 figures, submitted to Microelectronics Reliability (Special Issue: 31st European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, ESREF 2020

Vertical breakdown of GaN on Si due to V-pits

Gallium nitride on silicon (GaN/Si) is an important technological approach for power electronic devices exhibiting superior performance compared to devices based on a pure silicon technology. However, the material defect density in GaN/Si is high, and identification of critical defects limiting device reliability is still only partially accomplished because of experimental difficulties. In this work, atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, and cathodoluminescence were employed to investigate commonly occurring epitaxial overgrown V-pits and inhomogeneous incorporation of oxygen and carbon across layer stacking in the vertical direction. These experiments identified V-pits as regions with higher n-type carrier concentrations and paths for vertical leakage through the buffer, as directly probed by conductive atomic force microscopy. The deleterious effect of V-pits on device performance is demonstrated by evaluating test devices fabricated on two wafers with significantly diverse density of buried V-pits induced by varying growth conditions of the aluminum nitride nucleation layer. A clear correlation between observed vertical breakdown and density of V-pits within the C-doped GaN layer below the device structures is obtained. Back-gating transient measurements also show that the dynamic device behavior is affected by the V-pit density in terms of the detrapping time constants.Gallium nitride on silicon (GaN/Si) is an important technological approach for power electronic devices exhibiting superior performance compared to devices based on a pure silicon technology. However, the material defect density in GaN/Si is high, and identification of critical defects limiting device reliability is still only partially accomplished because of experimental difficulties. In this work, atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, and cathodoluminescence were employed to investigate commonly occurring epitaxial overgrown V-pits and inhomogeneous incorporation of oxygen and carbon across layer stacking in the vertical direction. These experiments identified V-pits as regions with higher n-type carrier concentrations and paths for vertical leakage through the buffer, as directly probed by conductive atomic force microscopy. The deleterious effect of V-pits on device performance is demonstrated by evaluating test devices fabricated on two wafers with s..

Reduced Nearshore Warming Associated With Eastern Boundary Upwelling Systems

Coastal marine biodiversity within eastern boundary upwelling systems (EBUS) is closely linked to the cooler sea temperatures associated with them. It has been suggested that global warming could lead to enhanced sea surface cooling in EBUS via the intensification of upwelling-favorable winds. Conversely, increased stratification and the widespread warming of the world’s oceans could drive these systems in the opposite direction. These competing mechanisms hold the potential for driving the thermal envelopes of EBUS toward – or away from – the thermal envelopes found outside EBUS, with likely contrasting implications for biodiversity conservation in each scenario. Here we characterize the patterns of net sea surface warming rates over more than three decades throughout the global ocean to evaluate if waters inside EBUS are changing differently from those outside EBUS. Results point to a trend of reduced warming inside EBUS, especially along the nearshore. We found that reduced net warming was prevalent in Pacific EBUS but restricted in Atlantic EBUS. In contrast, net warming in the coastal ocean outside EBUS was pervasive and generally associated with proximity to land. Our results suggest that EBUS have been responding to climate change differently from the rest of the global ocean, potentially buffering coastal biomes from decades of global warming

Compact Modeling of Nonideal Trapping/Detrapping Processes in GaN Power Devices

Compact modeling of charge trapping processes in GaN transistors is of fundamental importance for advanced circuit design. The goal of this article is to propose a methodology for modeling the dynamic characteristics of GaN power HEMTs in the realistic case where trapping/detrapping kinetics are described by stretched exponentials, contrary to ideal pure exponentials, thus significantly improving the state of the art. The analysis is based on: 1) an accurate methodology for describing stretched-exponential transients and extracting the related parameters and 2) a novel compact modeling approach, where the stretched exponential behavior is reproduced via multiple RC networks, whose parameters are specifically tuned based on the results of 1). The developed compact model is then used to simulate the transient performance of the HEMT devices as a function of duty cycle and frequency, thus providing insight on the impact of traps during the realistic switching operatio

A film-forming graphene/diketopyrrolopyrrole covalent hybrid with far-red optical features: Evidence of photo-stability

A dianiline derivative of a symmetric donor-acceptor-donor diketopyrrolopyrrole-based dye is employed for the two-sided covalent functionalization of liquid exfoliated few layers graphene flakes, through a direct arylation reaction. The resulting nanohybrid features the properties of a polymeric species, being solution-processed into homogeneous thin films, featuring a pronounced red-shift of the main absorption band with respect to the model dye unit and energy levels comparable to those of common diketopyrrolopyrrole-based polymers. A good electrical conductivity and the absence of radical signals generated after intense white light illumination, as probed through electron paramagnetic resonance, suggest a possible future application of this composite ma- terial in the field of photoprotective, antistatic layers with tunable colors