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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]

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]

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]

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]

The gate reliability of p-GaN gate AlGaN/GaN high electron mobility transistors with a ring-gate structure is investigated by step-stress experiments under a gate bias, combined with electroluminescence imaging and pulsed measurements. For gate stress (${V} _{\text {Gstress}}$) from 0 to 13 V, the drain current is found to be stable and decreases at 13 V at OFF-state and increases at ON-state. For ${V} _{\text {Gstress}}$ from 13 to 31 V, the drain current increases at OFF-state and decreases at ON-state, whereas ${V} _{\text {TH}}$ is stable and increases slightly. The changes in drain current characteristic and ${V} _{\text {TH}}$ values of the device after applying various ${V} _{\text {Gstress}}$ are associated with the injection and trapping of holes from the p-GaN layer to the AlGaN layer, supported by the results of pulsed measurements and by the simulation of energy band diagrams. When ${V} _{\text {Gstress}}$ is further increased to a high voltage of 31 V, ${V} _{\text {TH}}$ becomes noisy and a strong luminescence signal occurs with a sudden reduction in the drain current, and finally, a catastrophic failure happens in the gate-channel region. [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]