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Herein, the results are reviewed concerning reliability of high‐electron mobility transistors (HEMTs) based on GaN, which currently represent the technology of choice for high‐efficiency microwave and millimeter‐wave power amplifiers. Several failure mechanisms of these devices are extensively studied, including converse piezoelectric effects, formation of conductive percolation paths at the edge of gate toward the drain, surface oxidation of GaN, time‐dependent breakdown of GaN buffer, and of field‐plate dielectric. For GaN HEMTs with scaled gate length, the simultaneous control of short‐channel effects, deep‐level dispersion, and hot‐electron‐induced degradation requires a careful optimization of epitaxial material quality and device design. [ABSTRACT FROM AUTHOR]

The defectiveness of InGaN-based quantum wells increases with low indium contents, due to the compressive strain induced by the lattice mismatch between the InGaN and GaN layers, and to the stronger incorporation of defects favored by the presence of indium. Such defects can limit the performance and the reliability of LEDs, since they can act as non-radiative recombination centers, and favor the degradation of neighboring semiconductor layers. To investigate the location of the layers mostly subjected to degradation, we designed a color-coded structure with two quantum wells having different indium contents. By leveraging on numerical simulations, we explained the experimental results in respect of the ratio between the emissions of the two main peaks as a function of current. In addition, to evaluate the mechanisms that limit the reliability of this type of LED, we performed a constant-current stress test at high temperature, during which we monitored the variation in the optical characteristics induced by degradation. By comparing experimental and simulated results, we found that degradation can be ascribed to an increment of traps in the active region. This process occurs in two different phases, with different rates for the two quantum wells. The first phase mainly occurs in the quantum well closer to the p-contact, due to an increment of defectiveness. Degradation follows an exponential trend, and saturates during the second phase, while the quantum well close to the n-side is still degrading, supporting the hypothesis of the presence of a diffusive front that is moving from the p-side towards the n-side. The stronger degradation could be related to a lowering of the injection efficiency, or an increment of SRH recombination driven by a recombination-enhanced defect generation process. [ABSTRACT FROM AUTHOR]

Herein, the main factors and mechanisms that limit the reliability of gallium nitride (GaN)‐based light‐emitting diodes (LEDs) are reviewed. An overview of the defects characterization techniques most relevant for wide‐bandgap diodes is provided first. Then, by introducing a catalogue of traps and deep levels in GaN and computer‐aided simulations, it is shown which types of defects are more detrimental for the radiative efficiency of the devices. Gradual degradation mechanisms are analyzed in terms of their specific driving force: a separate analysis of recombination‐enhanced processes, driven by nonradiative recombination and/or temperature‐assisted processes, such as defects or impurity diffusion, is presented. The most common lifetime estimation methods and standards adopted for solid‐state luminaires are also reported on. Finally, the paper concludes by examining which are the typical degradation and failure mechanisms exhibited by LEDs submitted to electrical overstress. [ABSTRACT FROM AUTHOR]

We investigate the density of defects and the degradation rate in InGaN light-emitting diodes having identical dislocation density and epitaxial structure, but different indium content in the quantum well (QW; 12%, 16%, 20%). Our results, based on combined steady-state photocapacitance, light-capacitance voltage, and degradation measurements indicate that: (a) the density of defects in the superlattice underlayer is identical for the three wafers, indicating good and reproducible growth conditions; (b) the density of defects within the active region of the devices shows a monotonic dependence on the indium content in the QWs. These results, consistent with previous studies on the topic, prove unequivocally the important role of indium in favoring the incorporation of point defects, further clarifying the possible mechanisms of defect formation, and give a quantitative assessment of the related effect; (c) in step-stress experiments, the degradation rate was found to be much stronger for devices having high indium content in the QW. This result can be explained by considering a decrease in injection efficiency due to the generation or transport of defects, or an increment in defect-assisted Auger recombination terms due to the propagation of defects. [ABSTRACT FROM AUTHOR]

This article reports the first comprehensive analysis of the reliability of hydrogen-terminated diamond metal semiconductor field-effect transistors (MESFETs) submitted to OFF-state stress. We demonstrate that stress induces an increase in ON-resistance and a shift in the threshold voltage, along with a decrease in the transconductance peak value. These effects are ascribed to the generation of defects at the diamond surface and/or in the upper semiconductor layers. The defects are generated both in the access regions and under the gate, and their activation energy is 0.30 eV. [ABSTRACT FROM AUTHOR]

This paper shows that vertical GaN-on-GaN p–i–n diodes are able to withstand long-term operation in moderate avalanche conduction regime, thus proving the excellent stability of the gallium nitride material system. Under constant stress in stronger avalanche regime, the devices show a significant increase in the series resistance, a slight increase in forward voltage and a measurable increase in avalanche voltage. Degradation is ascribed to the generation of defects, a process which is likely occurring in the intrinsic region. The time-dependence of the performance loss is explained by considering the simultaneous presence of field-assisted trapping in the avalanche region and of charge de-trapping in the medium-field region of the devices. An interpretative model based on these assumptions is proposed to explain the full set of the experimental data. [ABSTRACT FROM AUTHOR]

In this article, we present the results of on-wafer short-term (24 h) stress tests carried out on 0.25-μm AlGaN/GaN HEMTs. Devices on-wafer were submitted to 24-h dc tests, at various gate and drain voltage values corresponding to dissipated power densities PD up to 40 W/mm, with estimated channel temperature ≅ 375 °C. GEN1 devices adopted a Ni/Pt/Au gate metallization and conventional plasma-enhanced chemical vapor deposition (PE-CVD) SiN passivation; in GEN2 devices, a modified gate metallization and a two-layer SiN passivation were adopted. When tested at Pd > 25 W/mm, a substantial decrease of drain current ID and transconductance gm was measured in GEN1 HEMTs, without any significant shift of threshold voltage. Failure analysis revealed that Au and O interdiffusion took place from the sidewalls; Au gradually substituted Ni as a Schottky contact, while O, in the presence of high electric field, high temperature, and high current, promoted (Al)GaN oxidation and pitting. On the contrary, negligible degradation was found after high temperature storage of GEN1 devices without applied bias, up to 450 °C. In GEN2, process modification was effective in reducing the impact of this failure mechanism, resulting in only 5% gm decrease after 24 h at a junction temperature of 375 °C with PD = 38 W/mm. Results demonstrate the effectiveness of the adopted on-wafer screening methodology in identifying potentially dangerous failure mechanisms. [ABSTRACT FROM AUTHOR]

This article reviews most recent results on the reliability of vertical GaN‐based devices, by presenting a few case studies focused on the stability and degradation of high‐voltage GaN‐on‐GaN diodes and of GaN‐based field‐effect transistors (FETs). With regard to diodes, two relevant stress conditions are investigated. The first is operation at high forward current that can induce a degradation of the electrical properties of the devices, mostly consisting in an increase in the operating voltage, well correlated to a decrease in the electroluminescence signal emitted by the diodes. This degradation process is ascribed to the diffusion of hydrogen from the highly p‐type doped regions toward the junction, with consequent compensation of the acceptor (Mg) dopant. The second stress regime investigated on diodes is avalanche: specifically, it is shown that polarization‐doped GaN devices may show avalanche capability, and the stability of diodes in avalanche regime is investigated in detail. With regard to transistors, the analysis is focused on GaN‐on‐GaN vertical Fin‐FETs. First, the stability of the threshold voltage under positive gate stress is analyzed, and the role of interface/oxide traps is discussed by experimental characterization. Then, the degradation under positive gate or high‐drain stress is investigated, to provide information on the dominant degradation processes. [ABSTRACT FROM AUTHOR]

This work investigates the degradation processes affecting the long-term reliability of 1.3 μm InAs quantum-dot lasers epitaxially grown on silicon. By submitting laser samples to constant-current stress, we were able to identify the physical mechanisms responsible for the optical degradation. More specifically, the samples (i) exhibited a gradual increase in threshold current, well correlated with (ii) a decrease in sub-threshold emission, and (iii) a decrease in slope efficiency. These variations were found to be compatible with a diffusion process involving the propagation of defects toward the active region of the device and the subsequent decrease in injection efficiency. This hypothesis was also supported by the increase in the defect-related current conduction components exhibited by the electrical characteristics, and highlights the role of defects in the gradual degradation of InAs quantum dot laser diodes. Electroluminescence measurements were used to provide further insight in the degradation process. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the degradation mechanisms of UV-B AlGaN-based light-emitting diodes (LEDs) submitted to constant current stress beyond the typical application conditions. We demonstrate the existence of two main degradation mechanisms that significantly impact the relative amplitude of the main quantum well (QW) peak at 310 nm and of a parasitic peak at ~340 nm related to the electron overflow toward the last quantum barrier before the p-side. These mechanisms are thoroughly investigated by means of electrical and optical measurements, and by photocurrent (PC) spectroscopy. We demonstrate that in the first 50 h of stress, degradation is caused by an increased defect density in the last quantum barrier and/or carrier escape from the QWs, which results in a decrease in the QW emission and in an increase in the parasitic peak at 340 nm. For longer stress times, degradation is dominated by a diffusion process, causing an increase in defect density and nonradiative recombination in the LED. This has a direct impact on both the QW peak and the parasitic peak, which show a significant decrease for long stress times. PC spectroscopy demonstrates that the defects responsible for degradation are most likely located next to mid-gap, thus acting as efficient nonradiative recombination centers. [ABSTRACT FROM AUTHOR]

We present an extensive analysis of the physical mechanisms responsible for the degradation of 1.3- $\mu \text{m}$ InAs quantum dot lasers epitaxially grown on Si, for application in silicon photonics. For the first time, we characterize the degradation of the devices by combined electro-optical measurements, electroluminescence spectra, and current-voltage analysis. We demonstrate the following original results: when submitted to a current step-stress experiment: 1) QD lasers show a measurable increase in threshold current, which is correlated to a decrease in slope efficiency; 2) the degradation process is stronger, when devices are stressed at current higher than 200 mA, i.e., in the stress regime, where both ground-state and excited-state emission are present; and 3) in the same range of stress currents, an increase in the defect-related current components is also detected, along with a slight decrease in the series resistance. Based on the experimental evidence collected within this paper, the degradation of QD lasers is ascribed to a recombination-enhanced defect reaction (REDR) process, activated by the escape of electrons out of the quantum dots. [ABSTRACT FROM AUTHOR]

With this paper, we review several different failure mechanisms of commercial light emitting diodes operating in real-life applications. We consider both high power and mid power devices, which represent the biggest share of the market. Real-life applications are particularly interesting since they reveal potential reliability issues and weaknesses of the optoelectronic devices, which are not detected/studied during conventional laboratory testing, due to their extrinsic origin. The analyzed failures mechanisms are mainly due to: 1) electrical overstress (surge and hot plugging); 2) assembly issues; 3) mishandling; and 4) chemical contamination. The results presented within this paper provide relevant data for the improvement of the reliability and robustness of current solid-state lighting systems. [ABSTRACT FROM AUTHOR]