Impact of Generation and Relocation of Defects on Optical Degradation of Multi-Quantum-Well InGaN/GaN-Based Light-Emitting Diode.

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.

Trap-state mapping to model GaN transistors dynamic performance.

Trapping phenomena degrade the dynamic performance of wide-bandgap transistors. However, the identification of the related traps is challenging, especially in presence of non-ideal defects. In this paper, we propose a novel methodology (trap-state mapping) to extract trap parameters, based on the mathematical study of stretched exponential recovery kinetics.

Challenges and Perspectives for Vertical GaN-on-Si Trench MOS Reliability: From Leakage Current Analysis to Gate Stack Optimization.

The vertical Gallium Nitride-on-Silicon (GaN-on-Si) trench metal-oxide-semiconductor field effect transistor (MOSFET) is a promising architecture for the development of efficient GaN-based power transistors on foreign substrates for power conversion applications. This work presents an overview of recent case studies, to discuss the most relevant challenges related to the development of reliable vertical GaN-on-Si trench MOSFETs. The focus lies on strategies to identify and tackle the most relevant reliability issues.

Understanding the Leakage Mechanisms and Breakdown Limits of Vertical GaN-on-Si pnn Diodes: The Road to Reliable Vertical MOSFETs.

This work investigates pnn GaN-on-Si vertical structures, through dedicated measurements and TCAD simulations, with the ultimate goal of identifying possible strategies for leakage and breakdown optimization. First, the dominant leakage processes were identified through temperature-dependent current-voltage characterization. Second, the breakdown voltage of the diodes was modelled through TCAD simulations based on the incomplete ionization of Mg in the p GaN layer.

Gradual Degradation of InGaAs LEDs: Impact on Non-Radiative Lifetime and Extraction of Defect Characteristics.

We present a detailed analysis of the gradual degradation mechanisms of InGaAs Light-Emitting Diodes (LEDs) tuned for optical emission in the 1.45-1.65 μm range.

Use of Bilayer Gate Insulator in GaN-on-Si Vertical Trench MOSFETs: Impact on Performance and Reliability.

We propose to use a bilayer insulator (2.5 nm AlO + 35 nm SiO2) as an alternative to a conventional uni-layer AlO (35 nm), for improving the performance and the reliability of GaN-on-Si semi vertical trench MOSFETs. This analysis has been performed on a test vehicle structure for module development, which has a limited OFF-state performance.

Vertical Leakage in GaN-on-Si Stacks Investigated by a Buffer Decomposition Experiment.

We investigated the origin of vertical leakage and breakdown in GaN-on-Si epitaxial structures. In order to understand the role of the nucleation layer, AlGaN buffer, and C-doped GaN, we designed a sequential growth experiment. Specifically, we analyzed three different structures grown on silicon substrates: AlN/Si, AlGaN/AlN/Si, C:GaN/AlGaN/AlN/Si.

Reliability of Blue-Emitting Eu-Doped Phosphors for Laser-Lighting Applications.

This paper investigates the reliability of blue-emitting phosphors for Near-UV (NUV) laser excitation. By means of a series of thermal stress experiments, and of stress under high levels of optical excitation, we have been able to identify the physical process responsible for the degradation of Eu-activated alkaline-earth halophosphate phosphors under typical and extreme operating conditions. In particular, for temperatures equal to or greater than 450 °C the material exhibited a time-dependent drop in the Photo-Luminescence (PL), which was attributed to the thermally induced ionization of the Eu optically active centers.

GaN-Based Laser Wireless Power Transfer System.

The aim of this work is to present a potential application of gallium nitride-based optoelectronic devices. By using a laser diode and a photodetector, we designed and demonstrated a free-space compact and lightweight wireless power transfer system, whose efficiency is limited by the efficiency of the receiver. We analyzed the effect of the electrical load, temperature, partial absorption and optical excitation distribution on the efficiency, by identifying heating and band-filling as the most impactful processes.

Laser-Based Lighting: Experimental Analysis and Perspectives.

This paper presents an extensive analysis of the operating principles, theoretical background, advantages and limitations of laser-based lighting systems. In the first part of the paper we discuss the main advantages and issues of laser-based lighting, and present a comparison with conventional LED-lighting technology. In the second part of the paper, we present original experimental data on the stability and reliability of phosphor layers for laser lighting, based on high light-intensity and high-temperature degradation tests.