Maurizio Moschetti

An experimental and numerical study of the on-resistance degradation in AlGaN/GaN-based technology is presented. Back-bias measurements on transmission-line-method (TLM) structures were performed to investigate the mechanism underlying the current degradation. The observed TLM current collapse exhibits Arrhenius behavior, which is associated with traps in the buffer layers. Interestingly, the decay time of the collapse shows a decreasing trend with increasing applied bias, which is here investigated and newly interpreted as a signature of Poole–Frenkel bias-enhanced trap emission. An effective model is discussed and implemented in TCAD simulations to support the experimental findings. In addition to providing justification for the temperature and applied-voltage dependence of the observed degradation trends, the proposed mechanism can also explain the spread in the activation energies measured for acceptor traps in the buffer layers, as reported in the literature for AlGaN/GaN technologies.

In this work, we present a comprehensive analysis of the back-effect phenomenon in Schottky p-GaN gate AlGaN/GaN high-electron-mobility transistors (HEMTs). By investigating different device structures, we emphasize the critical role played by the gate terminal in the device’s performance. Our study focuses on two main factors that significantly impact the current degradation caused by the back-effect: the magnesium (Mg) concentration in the p-GaN layer and gate polarization (V ${}_{\text {GS}}\text {)}$ . Finally, we propose a physics-based model supported by experimental data to provide further insights and details into this phenomenon, providing important indication to find the best tradeoff in the development of GaN HEMTs operating in monolithic half-bridge configuration.

In this work, a novel understanding of the main failure mechanism of a Schottky p-GaN gate AlGaN/GaN HEMT subject to forward gate stress is reported. First an experimental characterization of the gate leakage current (I_GSS) at different temperatures is reported. Then, Technology Computer Aided Design (TCAD) simulations are used to reproduce the experimental I_GSS thanks to the impact ionization model, also at different temperatures. Simulation results underline how the stressed regions for the Device Under Test (DUT) at high gate biases are the Schottky/p-GaN interface, the p-GaN/AlGaN barrier interface, and p-GaN sidewalls. Moreover, Time Dependent Gate Breakdown (TDGB) measurements were done, and the TEM analysis on the failed device showed the lattice crystal damage located at the p-GaN/AlGaN interface, in accordance with TCAD simulations’ current density distribution at high voltage gate stress.

In this letter, we investigate the dynamic-R_ON drift of monolithic Bidirectional AIGaN/GaN HEMTs. To this end, a novel measurement setup is proposed to evaluate the impact of the substrate connection. Particularly, (i) grounded and (ii) floating substrate configurations are compared. The partial recovery of the R_ON-degradation at high stress voltage is demonstrated, for the first time, on Bidirectional GaN devices with grounded substrate. Conversely, a higher R_ON-drift is observed with floating substrate configuration, due to the negative back-bias effect experienced during on-state time interval. This extends the knowledge on this topic, providing physical insights into the large degradation observed in previous work by highlighting the detrimental effect of leaving the substrate floating in Bidirectional power switches.

In this brief, we investigate the correlation between dynamic- ${Q}_{\text {OSS}}$ and dynamic- ${R}_{\text {ON}}$ of 650-V packaged AlGaN/GaN high-electron-mobility transistors (HEMTs). To this end, a novel measurement setup is proposed to evaluate the on-the-fly evolution of both parameters during conventional switch-mode operations. The measurements performed at ${V}_{\text {DS}} =200$ V show that the dynamic- ${R}_{\text {ON}}$ and dynamic- ${Q}_{\text {OSS}}$ present similar exponential transients and time constants, potentially explained by the ionization of C-related acceptors in the GaN buffer. The same activation energy ( ${E}_{\text {A}}\text {)}$ has been observed for both ${Q}_{\text {OSS}}$ and ${R}_{\text {ON}}$ , suggesting that their drifts are related to the same physical mechanism. The characterization has also been performed at different ${V}_{\text {DS}}$ levels, indicating that the observed correlation holds in the entire range up to 520 V.

The role of the magnesium (Mg) doping and its electrical activation on the off-state of p-GaN/AlGaN/GaN HEMTs has been investigated in this work. Firstly, the effect of different Mg doping profiles has been studied via the help of Technology Computer-Aided Design (TCAD) simulations, with the objective of analyzing the band diagrams of the structure. Then, it has been shown how experimental Capacitance–Voltage measurements can be useful to obtain information on the net acceptor concentration in the p-GaN. As a result, devices with an undoped (magnesium-free) GaN gate have been experimentally compared to devices whose p-GaN gate has been activated via a reference annealing process. Finally, results on a device characterized by an improved p-GaN activation have been presented and compared, showing improvements on several parameters of both off- and on-state, thus underlining the key role of the Mg activation process in the overall performances of normally-off GaN HEMTs.

In this work, threshold voltage instability of normally off p-GaN high electron mobility transistors has been investigated by monitoring the gate current density during a device on-state. The origin of gate current variations under stress has been ascribed to charge trapping occurring at different interfaces in the metal/p-GaN/AlGaN/GaN system. In particular, depending on the stress bias level, electrons (V_G < 6 V) or holes (V_G > 6 V) are trapped, causing a positive or negative threshold voltage shift ΔV_TH, respectively. By monitoring the gate current variations at different temperatures, activation energies associated with the electrons and holes trapping could be determined and correlated with the presence of nitrogen (electron traps) or gallium (hole traps) vacancies. Moreover, the electrical measurements suggested the generation of a new electron-trap upon long-time bias stress, associated with the creation of crystallographic dislocation-like defects extending across different interfaces (p-GaN/AlGaN/GaN) of the gate stack.

Silicon carbide (SiC) is a compound semiconductor, which is considered as a possible alternative to silicon for particles and photons detection. Its characteristics make it very promising for the next generation of nuclear and particle physics experiments at high beam luminosity. Silicon Carbide detectors for Intense Luminosity Investigations and Applications (SiCILIA) is a project starting as a collaboration between the Italian National Institute of Nuclear Physics (INFN) and IMM-CNR, aiming at the realization of innovative detection systems based on SiC. In this paper, we discuss the main features of silicon carbide as a material and its potential application in the field of particles and photons detectors, the project structure and the strategies used for the prototype realization, and the first results concerning prototype production and their performance.