Wurtzite Gallium Phosphide via Chemical Beam Epitaxy: Impurity-Related Luminescence vs Growth Conditions.

The metastable wurtzite crystal phase in gallium phosphide (WZ GaP) is a relatively new structure with little available information about its emission properties compared to the most stable zinc-blend phase. Here, the effect of growth conditions of WZ GaP nano- and microstructures obtained via chemical beam epitaxy on the optical properties was studied using power- and temperature-dependent photoluminescence (PL). We showed that the PL spectra are dominated by two strong broad emission bands at 1.68 and 1.88 eV and two relatively narrow peaks at 2.04 and 2.09 eV. The broad emissions are associated with the presence of carbon and a small number of extended crystal defects, respectively. For the sharp emissions, two main radiative recombination channels were observed with ionization energies estimated in the range of 50-80 meV and lower than 10 meV. No variation of the low-temperature PL spectra was observed for samples grown at different P precursor flows, while increasing Ga content enhanced the dominant broad emission at around 1.68 eV, suggesting that the group III organometallic precursor is the main source of impurities. Finally, Be-doped samples were grown, and their characteristic optical emission at 2.03 eV was identified. These results contribute to the understanding of impurity-related luminescence in hexagonal GaP, being useful for further crystal growth optimization required for the fabrication of optoelectronic devices.

Assessment of Active Dopants and p-n Junction Abruptness Using In Situ Biased 4D-STEM.

A key issue in the development of high-performance semiconductor devices is the ability to properly measure active dopants at the nanometer scale. In a p-n junction, the abruptness of the dopant profile around the metallurgical junction directly influences the electric field. Here, a contacted nominally symmetric and highly doped (NA = ND = 9 × 1018 cm-3) silicon p-n specimen is studied through in situ biased four-dimensional scanning transmission electron microscopy (4D-STEM). Measurements of electric field, built-in voltage, depletion region width, and charge density are combined with analytical equations and finite-element simulations in order to evaluate the quality of the junction interface. It is shown that all the junction parameters measured are compatible with a linearly graded junction. This hypothesis is also consistent with the evolution of the electric field with bias as well as off-axis electron holography data. These results demonstrate that in situ biased 4D-STEM can allow a better understanding of the electrostatics of semiconductor p-n junctions with nm-scale resolution.

The Demographic and Clinical Characteristics of Ulcerative Colitis in a Northeast Brazilian Population.

INTRODUCTION: The purpose of this study was to describe the clinical and demographic characteristics of UC in Bahia, a Brazilian state, and to identify the variables associated with extensive colitis, steroid therapy, immunosuppression, and colectomy. METHODS: In this cross-sectional study UC patients were interviewed, and additional information was collected from the medical records. Descriptive statistics and multivariate Poisson regression analysis were used. RESULTS: This study included 267 individuals, the mean age of whom was 39.4 years at diagnosis. There was a predominance of females and left-side colitis. Extensive colitis was positively associated with male gender, diarrhea, weight loss, and a younger age at diagnosis. In contrast, active smoking and a family history of IBD were negatively associated with extensive colitis. Positive associations were observed between steroid therapy and diarrhea, weight loss, urban patients, extraintestinal manifestations (EIMs), and hospitalization. Younger age and weight loss at diagnosis, a family history of IBD, extensive colitis, EIMs, hospitalization, and steroid therapy were all positively associated with immunosuppression. In contrast, Caucasian individuals, smokers, patients with rectal bleeding, and rural patients areas were all observed to have a decreased likelihood of immunosuppression. CONCLUSIONS: Our results corroborate the association between higher prevalence of extensive colitis and younger age at diagnosis. An association between steroid therapy and clinical presentation at diagnosis was observed. The observation that white individuals and rural patients use less immunosuppressive drugs highlights the need to study the influence of environmental and genetic factors on the behavior of UC in this population.

Epidemiology, demographic characteristics and prognostic predictors of ulcerative colitis.

Ulcerative colitis (UC) is a chronic disease characterized by diffuse inflammation of the mucosa of the colon and rectum. The hallmark clinical symptom of UC is bloody diarrhea. The clinical course is marked by exacerbations and remissions, which may occur spontaneously or in response to treatment changes or intercurrent illnesses. UC is most commonly diagnosed in late adolescence or early adulthood, but it can occur at any age. The incidence of UC has increased worldwide over recent decades, especially in developing nations. In contrast, during this period, therapeutic advances have improved the life expectancy of patients, and there has been a decrease in the mortality rate over time. It is important to emphasize that there is considerable variability in the phenotypic presentation of UC. Within this context, certain clinical and demographic characteristics are useful in identifying patients who tend to have more severe evolution of the disease and a poor prognosis. In this group of patients, better clinical surveillance and more intensive therapy may change the natural course of the disease. The aim of this article was to review the epidemiology and demographic characteristics of UC and the factors that may be associated with its clinical prognosis.