scispace - formally typeset
Search or ask a question
Author

M. La Grassa

Bio: M. La Grassa is an academic researcher from University of Padua. The author has contributed to research in topics: Quantum tunnelling & Thermionic emission. The author has an hindex of 3, co-authored 6 publications receiving 102 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, they proposed a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters.
Abstract: This paper reports an investigation of the physical origin of the thermal droop (the drop of the optical power at high temperatures) in InGaN-based light-emitting diodes. We critically investigate the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon-assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, we propose a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters. The model is based on a two-step phonon-assisted tunneling over an intermediate defective state, corrected in order to take into account the pure thermionic component at zero bias and the field-assisted term.

60 citations

Journal ArticleDOI
TL;DR: In this article, the deep levels related to non-radiative recombination in InGaN/GaN light-emitting diodes (LEDs) were investigated.
Abstract: This paper presents an extensive investigation of the deep levels related to non-radiative recombination in InGaN/GaN light-emitting diodes (LEDs). The study is based on combined optical and deep-level transient spectroscopy measurements, carried out on LEDs with identical structure and with different values of the non-radiative recombination coefficient. Experimental data lead to the following, relevant, results: (i) LEDs with a high non-radiative recombination coefficient have a higher concentration of a trap (labeled as “e2”) with an activation energy of 0.7 eV, which is supposed to be located close to/within the active region; (ii) measurements carried out with varying filling pulse duration suggest that this deep level behaves as a point-defect/dislocation complex. The Arrhenius plot of this deep level is critically compared with the previous literature reports, to identify its physical origin.

49 citations

Journal ArticleDOI
TL;DR: A correlation between the optical degradation and the accumulation of charge within the active region of the devices is demonstrated and experimental evidence is provided that the increase in SRH recombination is strongly related to the diffusion/build-up of charged defects within the Active Region of the Devices.

5 citations

Proceedings ArticleDOI
TL;DR: In this paper, the role of Shockley-Read-Hall (SRH) recombination and of the electron blocking layer (EBL) in the process of thermal droop was analyzed using numerical simulations and literature data.
Abstract: The thermal droop (reduction of the optical power when the temperature is increased) is a phenomenon that strongly limits the efficiency of InGaN-based light-emitting diodes. In this paper we analyze the role of Shockley-Read-Hall (SRH) recombination and of the electron blocking layer (EBL) in the process by using numerical simulations and literature data. The benefic impact of EBL suggests that carrier escape from the quantum wells gives a significant contribution to the thermal droop, therefore we review some of the mechanisms described in the literature (thermionic emission, phonon-assisted tunneling, thermionic trap-assisted tunneling). Since no formulation is able to fit the behavior of the measured SQW devices, we develop a new model based on two phonon-assisted tunneling steps through a defective state, extended in order to take into account zero-field emission. By using experimental data, material constants from the literature and only two fitting parameters the model is able to reproduce the experimental behavior.

3 citations

Journal ArticleDOI
TL;DR: An extensive analysis of the failure mechanisms of RGB (multi-chip) LEDs submitted to ESD testing indicates that red LEDs have an higher ESD robustness with respect to green and blue samples (based on InGaN), both under reverse and under forward bias test.

3 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The state-of-the-art fabrication of 2D and 3D heterostructures are reviewed, a critical survey of unique phenomena arising from forming 3D/2D interfaces are presented, and potential directions for research based on these new coupled architectures are discussed.
Abstract: Hybrid heterostructures are essential for functional device systems. The advent of 2D materials has broadened the material set beyond conventional 3D material-based heterostructures. It has triggered the fundamental investigation and use in applications of new coupling phenomena between 3D bulk materials and 2D atomic layers that have unique van der Waals features. Here we review the state-of-the-art fabrication of 2D and 3D heterostructures, present a critical survey of unique phenomena arising from forming 3D/2D interfaces, and introduce their applications. We also discuss potential directions for research based on these new coupled architectures. Integrating 3D bulk materials with 2D layered materials can harness promising properties and unique functions. This Review discusses the progress in the fabrication, physical coupling and potential applications of 3D/2D hybrid heterostructures.

201 citations

Journal ArticleDOI
TL;DR: In this paper, the role of deep defects in trapping in AlGaN/GaN, InAlN/AlGaN structures and transistors and in degradation of transistor parameters during electrical stress tests and after irradiation is discussed.
Abstract: New developments in theoretical studies of defects and impurities in III-Nitrides as pertinent to compensation and recombination in these materials are discussed. New results on experimental studies on defect states of Si, O, Mg, C, Fe in GaN, InGaN, and AlGaN are surveyed. Deep electron and hole traps data reported for GaN and AlGaN are critically assessed. The role of deep defects in trapping in AlGaN/GaN, InAlN/GaN structures and transistors and in degradation of transistor parameters during electrical stress tests and after irradiation is discussed. The recent data on deep traps influence on luminescent efficiency and degradation of characteristics of III-Nitride light emitting devices and laser diodes are reviewed.

186 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, they proposed a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters.
Abstract: This paper reports an investigation of the physical origin of the thermal droop (the drop of the optical power at high temperatures) in InGaN-based light-emitting diodes. We critically investigate the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon-assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, we propose a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters. The model is based on a two-step phonon-assisted tunneling over an intermediate defective state, corrected in order to take into account the pure thermionic component at zero bias and the field-assisted term.

60 citations

Journal ArticleDOI
TL;DR: In this paper, a unified model of the radiative and nonradiative recombination channels in a mixed formamidinium-cesium lead iodide perovskite was presented, including charge carrier trapping, de-trapping and accumulation, as well as higher-order recombination mechanisms.
Abstract: Trap‐related charge‐carrier recombination fundamentally limits the performance of perovskite solar cells and other optoelectronic devices. While improved fabrication and passivation techniques have reduced trap densities, the properties of trap states and their impact on the charge‐carrier dynamics in metal‐halide perovskites are still under debate. Here, a unified model is presented of the radiative and nonradiative recombination channels in a mixed formamidinium‐cesium lead iodide perovskite, including charge‐carrier trapping, de‐trapping and accumulation, as well as higher‐order recombination mechanisms. A fast initial photoluminescence (PL) decay component observed after pulsed photogeneration is demonstrated to result from rapid localization of free charge carriers in unoccupied trap states, which may be followed by de‐trapping, or nonradiative recombination with free carriers of opposite charge. Such initial decay components are shown to be highly sensitive to remnant charge carriers that accumulate in traps under pulsed‐laser excitation, with partial trap occupation masking the trap density actually present in the material. Finally, such modelling reveals a change in trap density at the phase transition, and disentangles the radiative and nonradiative charge recombination channels present in FA0.95Cs0.05PbI3, accurately predicting the experimentally recorded PL efficiencies between 50 and 295 K, and demonstrating that bimolecular recombination is a fully radiative process.

56 citations