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Gallium nitride (GaN) based high periodicity indium/GaN multiple quantum wells solar cells have recently been proposed for different applications: from operation in harsh environments, like space applications, to their use in concentrator solar harvesting system and wireless power transfer system. In this article, we extensively investigate the mechanisms, which influence the in-dark current-voltage characteristics of these device under no excitation by means of experimental measurements and numerical simulations performed with the technology computer-aided design (TCAD) Sentaurus suite from Synopsys. Two different nonlocal models are introduced: the first one considers intrabarrier tunneling, which was found to be the dominant conduction mechanism for voltages above the main diode turn-on; the second model considers trap-assisted tunneling, implemented through traps uniformly distributed in space and energy, to reproduce the current flow in the sub turn-on region. A good matching is obtained between the experimental and simulated electrical characteristics, by considering these nonlocal models in addition to the thermionic escape.

In this article, we present an extensive analysis of the positive threshold voltage instability in Schottky p-GaN gate enhancement-mode devices, investigated by a custom setup allowing an extended observation window, from the microsecond to hundreds of seconds. We show that a matrix of experiments can be specifically designed to investigate the voltage, temperature and leakage dependence of the threshold voltage instability induced by a positive gate bias, and to identify them. The original results indicate that the observed positive threshold voltage shift can be ascribed to the trapping of electrons at defects located in the AlGaN barrier. Remarkably, the trapping rate is strongly dependent on temperature at low bias, while it is not temperature-dependent at high bias, indicating the existence of both temperature and leakage-assisted trapping processes. This result was confirmed by investigating the correlation between dc leakage measurements and the time constant of threshold voltage transients. On the other hand, the recovery process is found to be thermally activated, with an activation energy of 0.26 eV: the trapped electrons are thermally emitted into the conduction band and are pushed toward the channel by the intrinsic electric field.

In this article, we present an analysis of the correlation between interface traps (ITs) and border traps (BTs) on distinctive features of ${C}$ – ${V}$ curves in vertical Al2O3/gallium-nitride (GaN) MOS capacitors. First, pulsed ${C}$ – ${V}$ curves were characterized during the application of quiescent gate bias stresses of different magnitudes and signs. This characterization revealed four main distinctive features: 1) rightward rigid shift; 2) leftward rigid shift; 3) decrease of the $\Delta {C}$ – $\Delta {V}$ slope; and 4) formation of a hump in a gate bias range before the accumulation of electrons at the oxide/semiconductor interface. By means of a combined experimental/simulation analysis, these features were univocally attributed to specific ITs or BTs in the overall trap distribution. The simulation-aided analysis enhances the physical understanding of the ${C}$ – ${V}$ curves features and increases the dependability of the adopted IT measurement technique, allowing for a more rapid process optimization and device technology development.

Application of gallium nitride high-electron-mobility transistors (GaN HEMTs) to millimeter-wave power amplifiers requires gate length scaling below 150 nm: in order to control short-channel effects, the gate-to-channel distance must be decreased, and the device epitaxial structure has to be completely redesigned. A high 2-D electron gas (2DEG) carrier density can be preserved even with a very thin top barrier layer by substituting AlGaN with AlN, InAl(Ga)N, or ScAlN. Moreover, to prevent interaction of hot electrons with compensating impurities and defects in the doped GaN buffer, the latter has to be separated from the channel by a back barrier. Other device designs consist in adopting a graded channel (which controls the electric field) or to adopt nitrogen-polar (N-polar) GaN growth (which decreases the distance between gate and channel, thus attenuating short-channel effects). The aim of this article is to review the various options for controlling short-channel effects, improve off-state characteristics, and reduce drain–source leakage current. Advantages and potential drawbacks of each proposed solution are analyzed in terms of current collapse (CC), dispersion effects, and reliability.

The kink effect in field-effect transistors (FETs) consists in a sudden increase in drain current, ${I}_{\text {D}}$ , during a drain voltage sweep and leading to a higher ${I}_{\text {D}}$ saturation value. We report new experimental data concerning the dynamic behavior of the “kink” in AlGaN/GaN HEMTs and correlate them with deep levels. The results demonstrate the role of the Poole–Frenkel effect in determining the occurrence of the kink and identify the experimental conditions that make it observable.

We discuss the degradation mechanisms of C-doped 0.15- $\mu \text{m}$ gate AlGaN/GaN HEMTs tested by drain step-stress experiments. Experimental results show that these devices exhibit cumulative degradation effects during the step-stress experiments in terms of either (i) transconductance ( $g_{\mathrm{ m}}$ ) decrease without any threshold-voltage ( $V_{\mathrm{ T}}$ ) change under OFF-state stress, or (ii) both $V_{\mathrm{ T}}$ increase and $g_{\mathrm{ m}}$ decrease under ON-state stress conditions. To aid the interpretation of the experiments, two-dimensional hydrodynamic device simulations were carried out. Based on the obtained results, we attribute the $g_{\mathrm{ m}}$ decrease accumulating under OFF-state stress to hole emission from CN acceptor traps in the gate-drain access region of the buffer, resulting in an increase in the drain access resistance. On the other hand, under ON-state stress, channel hot electrons are injected into the buffer under the gate and in the gate-drain region where they are captured by CN traps, leading to $V_{\mathrm{ T}}$ and $g_{\mathrm{ m}}$ degradation, respectively.

In the last years, the research on ultraviolet-C (UV-C) light emitting diodes (LEDs) focused its efforts on the solution of major problems that limited the emitted optical power (OP) and that caused the sudden failure of the devices. This led to the availability in the market of some devices with interesting electro-optical characteristics and promising lifetimes. In this article, we decided to study the reliability of four commercial UV-C LEDs with a nominal wavelength of 265 nm, in order to study their lifetime and their possible implementation in disinfection systems. We submitted the devices to an accelerated lifetime test of 20000 min, at the absolute maximum current indicated in their respective datasheets. During the tests, we carried out electrical and optical measurements, and we evaluated their spectral characteristics before and after aging. Once identified the best sample, we compared it with the best sample at 275 nm studied in our previous work, in order to show all the problems to consider if these LEDs have to be used in machinery that will be placed on the market.