http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

In this paper, we present a comprehensive reviewand discussion of the state-of-the-art device technology and application development of GaN-on-Si power electronics. Several device technologies for realizing normally off operation that is highly desirable for power switching applications are presented. In addition, the examples of circuit applications that can greatly benefit from the superior performance of GaN power devices are demonstrated. Comparisonwith other competingpower device technology, such as Si superjunction-MOSFET and SiC MOSFET, is also presented and analyzed. Critical issues for commercialization of GaN-on-Si power devices are discussed with regard to cost, reliability, and ease of use.

GaN-on-Si Power Technology: Devices and Applications

FinFETs and Other Multi-Gate Transistors provides a comprehensive description of the physics, technology and circuit applications of multigate field-effect transistors (FETs). It explains the physics and properties of these devices, how they are fabricated and how circuit designers can use them to improve the performances of integrated circuits. The International Technology Roadmap for Semiconductors (ITRS) recognizes the importance of these devices and places them in the "Advanced non-classical CMOS devices" category. Of all the existing multigate devices, the FinFET is the most widely known. FinFETs and Other Multi-Gate Transistors is dedicated to the different facets of multigate FET technology and is written by leading experts in the field.

/pdf/finfets-and-other-multi-gate-transistors-541arp307w.pdf

FinFETs and Other Multi-Gate Transistors

GaN-on-Si power switching transistors that use carbon-doped epitaxy are highly vulnerable to dynamic $\text{R}_{ON}$ dispersion, leading to reduced switching efficiency. In this paper, we identify the causes of this dispersion using substrate bias ramps to isolate the leakage paths and trapping locations in the epitaxy and simulation to identify their impact on the device characteristics. It is shown that leakage can occur both vertically and laterally, and we suggest that this is associated not only with bulk transport, but also with extended defects as well as hole gases at heterojunctions. For exactly the same epitaxial design, it is shown using a “leaky dielectric” model that depending on the leakage paths, dynamic $\text{R}_{ON}$ dispersion can vary between insignificant and infinite. An optimum leakage configuration is identified to minimize dispersion requiring a resistivity which increases with depth in the buffer stack. It is demonstrated that leakage through the undoped GaN channel is required over the entire gate to drain gap, and not just under the contacts, in order to fully suppress dispersion.

/pdf/leaky-dielectric-model-for-the-suppression-of-dynamic-r-2ho0i94ufm.pdf

“Leaky Dielectric” Model for the Suppression of Dynamic $R_{\mathrm{ON}}$ in Carbon-Doped AlGaN/GaN HEMTs

Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spontaneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high-voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench-structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics.

https://hal.archives-ouvertes.fr/hal-03421528/document

GaN-based power devices: Physics, reliability, and perspectives

We investigate the impact of the gate contact on the threshold voltage stability in p-GaN gate AlGaN/GaN heterojunction field-effect transistors with double pulse measurements on the p-GaN gate devices and device simulations. We find that, under gate stress, in the case of high-leakage Schottky contact, a negative threshold voltage shift results from hole accumulation in the p-GaN region. Conversely, in the case of low-leakage Schottky contact, hole depletion in the p-GaN region gives rise to a positive threshold voltage shift. More generally, we show that an imbalance between the hole tunneling current through the Schottky barrier and the thermionic current across the AlGaN barrier results in a variation of the total charge stored in the p-GaN region, which in turn is responsible for the observed threshold voltage shift. Finally, we present a simplified equivalent circuit model for the p-GaN gate module.

Threshold Voltage Instability in p-GaN Gate AlGaN/GaN HFETs

Pulse behavior of insulated-gate double-field-plate power AlGaN/GaN HEMTs with C-doped buffers showing small current-collapse effects and dynamic RDS,on increase can accurately be reproduced by numerical device simulations that assume the CN-CGa autocompensation model as carbon doping mechanism. Current-collapse effects much larger than experimentally observed are instead predicted by simulations if C doping is accounted by dominant acceptor states. This suggests that buffer growth conditions favoring CN-CGa autocompensation can allow for the fabrication of power AlGaN/GaN HEMTs with reduced current-collapse effects. The drain-source capacitance of these devices is found to be a sensitive function of the C doping model, suggesting that its monitoring can be adopted as a fast technique to assess buffer compensation properties.

Influence of Buffer Carbon Doping on Pulse and AC Behavior of Insulated-Gate Field-Plated Power AlGaN/GaN HEMTs

In this paper we present a derivation of a very convenient approach to include quantum confinement effects in drift-diffusion or hydrodynamic device simulators, without explicitly solving the Schrodinger equation. With respect to similar methods recently proposed in the literature, the presented approach has a few advantages: it does not depend on the transport model (drift-diffusion or hydrodynamic); it can straightforwardly include Fermi-Dirac statistics; it provides an additional degree of freedom for calibration, which is particularly useful for considering non planar device structures; finally, it can be discretized in such a way to exhibit very stable convergence properties.

Effective Bohm Quantum Potential for device simulators based on drift-diffusion and energy transport

In this paper, we present the main issues and the modelling approaches for the simulation of nanoscale MOSFETs in which transport is dominated by ballistic electrons. We show that is indeed possible to compute in an accurate way the density of states in the channel in the case of quantum confinement without solving the complete two-dimensional Schrodinger equation. We are developing modelling tools that can be applied to several types of MOSFET structures: bulk, strained-Si and ultra-thin SOI MOSFETs, FINFETs, double gate MOSFETs and Schottky barrier MOSFETs. Here, results for silicon germanium and bulk silicon devices with channel length of 25 nm are presented. In the present form, tools are limited to the case of fully ballistic transport, which might be reached by the extremely scaled MOSFETs at end of the Roadmap.

/pdf/modelling-and-simulation-challenges-for-nanoscale-mosfets-in-2n3ttgjs9w.pdf

Modelling and simulation challenges for nanoscale MOSFETs in the ballistic limit

A semiconductor device includes a first compound semiconductor material and a second compound semiconductor material on the first compound semiconductor material. The second compound semiconductor material comprises a different material than the first compound semiconductor material such that the first compound semiconductor material has a two-dimensional electron gas (2DEG). The semiconductor device further includes a buried field plate disposed in the first compound semiconductor material and electrically connected to a terminal of the semiconductor device. The 2DEG is interposed between the buried field plate and the second compound semiconductor material.

Gilberto Curatola

Papers

Threshold Voltage Instability in p-GaN Gate AlGaN/GaN HFETs

Influence of Buffer Carbon Doping on Pulse and AC Behavior of Insulated-Gate Field-Plated Power AlGaN/GaN HEMTs

Effective Bohm Quantum Potential for device simulators based on drift-diffusion and energy transport

Modelling and simulation challenges for nanoscale MOSFETs in the ballistic limit

Compound Semiconductor Device with Buried Field Plate