Influence of the reactor environment on the selective area thermal etching of GaN nanohole arrays

Selective area thermal etching (SATE) of gallium nitride is a simple subtractive process for creating novel device architectures and improving the structural and optical quality of III-nitride-based devices. In contrast to plasma etching, it allows, for example, the creation of enclosed features with extremely high aspect ratios without introducing ion-related etch damage. We report how SATE can create uniform and organized GaN nanohole arrays from c-plane and (11–22) semi-polar GaN in a conventional MOVPE reactor. The morphology, etching anisotropy and etch depth of the nanoholes were investigated by scanning electron microscopy for a broad range of etching parameters, including the temperature, the pressure, the NH3 flow rate and the carrier gas mixture. The supply of NH3 during SATE plays a crucial role in obtaining a highly anisotropic thermal etching process with the formation of hexagonal non-polar-faceted nanoholes. Changing other parameters affects the formation, or not, of non-polar sidewalls, the uniformity of the nanohole diameter, and the etch rate, which reaches 6 µm per hour. Finally, the paper discusses the SATE mechanism within a MOVPE environment, which can be applied to other mask configurations, such as dots, rings or lines, along with other crystallographic orientations

Complexity of dipolar exciton Mott transition in GaN/(AlGa)N nanostructures

The Mott transition from a dipolar excitonic liquid to an electron-hole plasma is demonstrated in a wide GaN/(Al,Ga)N quantum well at $T=7$K by means of spatially-resolved magneto-photoluminescence spectroscopy. Increasing optical excitation density we drive the system from the excitonic state, characterized by a diamagnetic behavior and thus a quadratic energy dependence on the magnetic field, to the unbound electron-hole state, characterized by a linear shift of the emission energy with the magnetic field. The complexity of the system requires to take into account both the density-dependence of the exciton binding energy and the exciton-exciton interaction and correlation energy that are of the same order of magnitude. We estimate the carrier density at Mott transition as $n_\mathrm{Mott}\approx 2\times 10^{11}$cm$^{-2}$ and address the role played by excitonic correlations in this process. Our results strongly rely on the spatial resolution of the photoluminescence and the assessment of the carrier transport. We show, that in contrast to GaAs/(Al,Ga)As systems, where transport of dipolar magnetoexcitons is strongly quenched by the magnetic field due to exciton mass enhancement, in GaN/(Al,Ga)N the band parameters are such that the transport is preserved up to $9$T.Comment: 15 pages 13 figure

Analysis of the characteristic temperatures of (Ga,In)(N,As)/GaAs laser diodes

The characteristic temperatures of the threshold current density, T0, and external differential quantum efficiency, T1, of a series of (Ga,In)(N,As)/GaAs quantum well (QW) laser diodes are measured in the wavelength range from 1 to 1.5μm. It is found that both T0 and T1 strongly decrease with increasing lasing wavelength. The origin of this degradation is shown to be, in the case of T0, mostly dominated by a decrease in the transparency current density characteristic temperature, an increase in the optical losses and a decrease in the modal gain. The degradation of T1 is mainly due to the increase in the optical losses. The effective carrier recombination lifetime in the QW is shown to decrease from 1.2 to 0.2 ns with N content up to 2%, in good agreement with previous reports that link this low lifetime to non-radiative monomolecular recombination through defects in the QW. Carrier leakage is ruled out as the dominant process degrading T0 and T1 on the basis of the temperature dependence of the effective carrier recombination lifetime

Polarized white light from hybrid organic/III-nitrides grating structures.

Highly polarised white light emission from a hybrid organic/inorganic device has been achieved. The hybrid devices are fabricated by means of combining blue InGaN-based multiple quantum wells (MQWs) with a one-dimensional (1D) grating structure and down-conversion F8BT yellow light emitting polymer. The 1D grating structure converts the blue emission from unpolarised to highly polarised; Highly polarised yellow emission has been achieved from the F8BT polymer filled and aligned along the periodic nano-channels of the grating structure as a result of enhanced nano-confinement. Optical polarization measurements show that our device demonstrates a polarization degree of up to 43% for the smallest nano-channel width. Furthermore, the hybrid device with such a grating structure allows us to achieve an optimum relative orientation between the dipoles in the donor (i.e., InGaN/GaN MQWs) and the diploes in the acceptor (i.e., the F8BT), maximizing the efficiency of non-radiative energy transfer (NRET) between the donor and the acceptor. Time-resolved micro photoluminescence measurements show a 2.5 times enhancement in the NRET efficiency, giving a maximal NRET efficiency of 90%. It is worth highlighting that the approach developed paves the way for the fabrication of highly polarized white light emitters

PI3Kγ Protects from Myocardial Ischemia and Reperfusion Injury through a Kinase-Independent Pathway

BACKGROUND: PI3Kgamma functions in the immune compartment to promote inflammation in response to G-protein-coupled receptor (GPCR) agonists and PI3Kgamma also acts within the heart itself both as a negative regulator of cardiac contractility and as a pro-survival factor. Thus, PI3Kgamma has the potential to both promote and limit M I/R injury. METHODOLOGY/PRINCIPAL FINDINGS: Complete PI3Kgamma-/- mutant mice, catalytically inactive PI3KgammaKD/KD (KD) knock-in mice, and control wild type (WT) mice were subjected to in vivo myocardial ischemia and reperfusion (M I/R) injury. Additionally, bone-marrow chimeric mice were constructed to elucidate the contribution of the inflammatory response to cardiac damage. PI3Kgamma-/- mice exhibited a significantly increased infarction size following reperfusion. Mechanistically, PI3Kgamma is required for activation of the Reperfusion Injury Salvage Kinase (RISK) pathway (AKT/ERK1/2) and regulates phospholamban phosphorylation in the acute injury response. Using bone marrow chimeras, the cardioprotective role of PI3Kgamma was mapped to non-haematopoietic cells. Importantly, this massive increase in M I/R injury in PI3Kgamma-/- mice was rescued in PI3Kgamma kinase-dead (PI3KgammaKD/KD) knock-in mice. However, PI3KgammaKD/KD mice exhibited a cardiac injury similar to wild type animals, suggesting that specific blockade of PI3Kgamma catalytic activity has no beneficial effects. CONCLUSIONS/SIGNIFICANCE: Our data show that PI3Kgamma is cardioprotective during M I/R injury independent of its catalytic kinase activity and that loss of PI3Kgamma function in the hematopoietic compartment does not affect disease outcome. Thus, clinical development of specific PI3Kgamma blockers should proceed with caution

The Italian registry of pulmonary non-tuberculous mycobacteria - IRENE:The study protocol

Background: A substantial increase in pulmonary and extra-pulmonary diseases due to non-tuberculous mycobacteria (NTM) has been documented worldwide, especially among subjects suffering from chronic respiratory diseases and immunocompromised patients. Many questions remain regarding the epidemiology of pulmonary disease due to NTM (NTM-PD) mainly because reporting of NTM-PD to health authorities is not mandated in several countries, including Italy. This manuscript describes the protocol of the first Italian registry of adult patients with respiratory infections caused by NTM (IRENE). Methods: IRENE is an observational, multicenter, prospective, cohort study enrolling consecutive adult patients with either a NTM respiratory isolate or those with NTM-PD. A total of 41 centers, including mainly pulmonary and infectious disease departments, joined the registry so far. Adult patients with all of the following are included in the registry: 1) at least one positive culture for any NTM species from any respiratory sample; 2) at least one positive culture for NTM isolated in the year prior the enrolment and/or prescribed NTM treatment in the year prior the enrolment; 3) given consent to inclusion in the study. No exclusion criteria are applied to the study. Patients are managed according to standard operating procedures implemented in each IRENE clinical center. An online case report form has been developed to collect patients' demographics, comorbidities, microbiological, laboratory, functional, radiological, clinical, treatment and outcome data at baseline and on an annual basis. An IRENE biobank has also been developed within the network and linked to the clinical data of the registry. Conclusions: IRENE has been developed to inform the clinical and scientific community on the current management of adult patients with NTM respiratory infections in Italy and acts as a national network to increase the disease's awareness

Monolithically integrated white light LEDs on (11-22) semi-polar GaN templates

Carrier transport issues in a (11–22) semi-polar GaN based white light emitting diode (consisting of yellow and blue emissions) have been investigated by detailed simulations, demonstrating that the growth order of yellow and blue InGaN quantum wells plays a critically important role in achieving white emission. The growth order needs to be yellow InGaN quantum wells first and then a blue InGaN quantum well after the growth of n-type GaN. The fundamental reason is due to the poor hole concentration distribution across the whole InGaN quantum well region. In order to effectively capture holes in both the yellow InGaN quantum wells and the blue InGaN quantum well, a thin GaN spacer has been introduced prior to the blue InGaN quantum well. The detailed simulations of the band diagram and the hole concentration distribution across the yellow and the blue quantum wells have been conducted, showing that the thin GaN spacer can effectively balance the hole concentration between the yellow and the blue InGaN quantum wells, eventually determining their relative intensity between the yellow and the blue emissions. Based on this simulation, we have demonstrated a monolithically multi-colour LED grown on our high quality semi-polar (11–22) GaN templates

Effect of the COVID-19 pandemic on surgery for indeterminate thyroid nodules (THYCOVID): a retrospective, international, multicentre, cross-sectional study

Background Since its outbreak in early 2020, the COVID-19 pandemic has diverted resources from non-urgent and elective procedures, leading to diagnosis and treatment delays, with an increased number of neoplasms at advanced stages worldwide. The aims of this study were to quantify the reduction in surgical activity for indeterminate thyroid nodules during the COVID-19 pandemic; and to evaluate whether delays in surgery led to an increased occurrence of aggressive tumours.Methods In this retrospective, international, cross-sectional study, centres were invited to participate in June 22, 2022; each centre joining the study was asked to provide data from medical records on all surgical thyroidectomies consecutively performed from Jan 1, 2019, to Dec 31, 2021. Patients with indeterminate thyroid nodules were divided into three groups according to when they underwent surgery: from Jan 1, 2019, to Feb 29, 2020 (global prepandemic phase), from March 1, 2020, to May 31, 2021 (pandemic escalation phase), and from June 1 to Dec 31, 2021 (pandemic decrease phase). The main outcomes were, for each phase, the number of surgeries for indeterminate thyroid nodules, and in patients with a postoperative diagnosis of thyroid cancers, the occurrence of tumours larger than 10 mm, extrathyroidal extension, lymph node metastases, vascular invasion, distant metastases, and tumours at high risk of structural disease recurrence. Univariate analysis was used to compare the probability of aggressive thyroid features between the first and third study phases. The study was registered on ClinicalTrials.gov, NCT05178186.Findings Data from 157 centres (n=49 countries) on 87 467 patients who underwent surgery for benign and malignant thyroid disease were collected, of whom 22 974 patients (18 052 [78 center dot 6%] female patients and 4922 [21 center dot 4%] male patients) received surgery for indeterminate thyroid nodules. We observed a significant reduction in surgery for indeterminate thyroid nodules during the pandemic escalation phase (median monthly surgeries per centre, 1 center dot 4 [IQR 0 center dot 6-3 center dot 4]) compared with the prepandemic phase (2 center dot 0 [0 center dot 9-3 center dot 7]; p<0 center dot 0001) and pandemic decrease phase (2 center dot 3 [1 center dot 0-5 center dot 0]; p<0 center dot 0001). Compared with the prepandemic phase, in the pandemic decrease phase we observed an increased occurrence of thyroid tumours larger than 10 mm (2554 [69 center dot 0%] of 3704 vs 1515 [71 center dot 5%] of 2119; OR 1 center dot 1 [95% CI 1 center dot 0-1 center dot 3]; p=0 center dot 042), lymph node metastases (343 [9 center dot 3%] vs 264 [12 center dot 5%]; OR 1 center dot 4 [1 center dot 2-1 center dot 7]; p=0 center dot 0001), and tumours at high risk of structural disease recurrence (203 [5 center dot 7%] of 3584 vs 155 [7 center dot 7%] of 2006; OR 1 center dot 4 [1 center dot 1-1 center dot 7]; p=0 center dot 0039).Interpretation Our study suggests that the reduction in surgical activity for indeterminate thyroid nodules during the COVID-19 pandemic period could have led to an increased occurrence of aggressive thyroid tumours. However, other compelling hypotheses, including increased selection of patients with aggressive malignancies during this period, should be considered. We suggest that surgery for indeterminate thyroid nodules should no longer be postponed even in future instances of pandemic escalation.Funding None.Copyright (c) 2023 Published by Elsevier Ltd. All rights reserved

Group-III nitride quantum heterostructures grown by molecular beam epitaxy

In the present paper, we address a review of group-III nitride quantum wells and quantum dots realized by molecular beam epitaxy (MBE) using ammonia as a nitrogen source. Some important features of the growth of nitrides by MBE using ammonia are pointed out. We also emphasize the role of in situ analysis tools such as reflection high-energy electron diffraction. The optical properties of several kinds of quantum heterostructure are presented. They illustrate well the combined effects of polarization fields and carrier localization. Finally, the use of InGaN/GaN QWs in LEDs for white light emission is presented