Performance enhancement of deep-ultraviolet LEDs by using quaternary AlInGaN polarization-engineered multiple-symmetrical-stair quantum barriers without electron blocking layer.

In this paper, a structure design using quaternary AlInGaN as multiple-symmetrical-stair-shaped quantum barriers without an electron blocking layer is shown. The results show this design mitigates the droop effect to ∼0.1%, and the internal quantum efficiency reaches about 93.4%. It is believed that the better performance results from balanced electron and hole concentration and distribution of the current among the quantum wells, along with reduced non-radiative recombination. This work may be useful in the application of using quaternary AlInGaN materials as quantum barrier layers with computational simulations to design structures with electron-barrier-free layers.

Prevalence and surveillance of tuberculosis in Yemen from 2006 to 2018.

Tuberculosis is a major public health issue in Yemen, a country located at the southwestern tip of the Arabian Peninsula, while the situation of tuberculosis had been further exacerbated since the war started in 2015. The objective of this study is to investigate the incidence of tuberculosis in Yemen before the outbreak of COVID-19, from 2006 to 2018. During the 13-year period, 92 482 patients were enrolled in the TB programme records from the 22 governorates. Almost equal number of cases were diagnosed between males and females (a male to female ratio, 1.03:1). A notable rising incidence was observed in all age groups starting from 2011. The sharpest increase occurred in children under age 15, rising by 8.0-fold from 0.5 in the period 2006-2010 to 4.1 in the period 2011-2018. Paediatric TB accounted for 9.6% of all reported cases. In terms of the patient residence, incidence has more than doubled in Sana'a city, Sana'a Gov., Hajjah and Saadah. Concomitant diseases with tuberculosis included diabetes mellitus (14.0%), brucellosis (6.1%), hepatitis (6.0%), rheumatoid arthritis (4.3%), renal disorders (2.5%) and HIV infection (2.5%). Development of interventions to reduce tuberculosis incidence in children and concomitant communicable diseases is urgently needed.

Water-bath assisted convective assembly of aligned silver nanowire films for transparent electrodes.

Manipulating Ag nanowire (AgNW) assembly to tailor the opto-electrical properties and surface morphology could improve the performance of next-generation transparent conductive electrodes. In this paper, we demonstrated a water-bath assisted convective assembly process at the temporary water/alcohol interface for fabricating hierarchical aligned AgNW electrodes. The convection flow plays an important role during the assembly process. The assembled AgNW film fabricated via three times orthogonal dip-coating at a water-bath temperature of 80 °C has a sheet resistance of 11.4 Ω sq(-1) with 89.9% transmittance at 550 nm. Moreover, the root mean square (RMS) of this assembled AgNW film was only 15.6 nm which is much lower than the spin-coated random AgNW film (37.6 nm) with a similar sheet resistance. This facile assembly route provides a new way for manufacturing and tailoring ordered nanowire-based devices.

Enhanced photovoltaic performance of organic/silicon nanowire hybrid solar cells by solution-evacuated method.

A method has been developed to fabricate organic-inorganic hybrid heterojunction solar cells based on n-type silicon nanowire (SiNW) and poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) hybrid structures by evacuating the PEDOT:PSS solution with dip-dropping on the top of SiNWs before spin-coating (solution-evacuating). The coverage and contact interface between PEDOT:PSS and SiNW arrays can be dramatically enhanced by optimizing the solution-evacuated time. The maximum power conversion efficiency (PCE) reaches 9.22% for a solution-evacuated time of 2 min compared with 5.17% for the untreated pristine device. The improvement photovoltaic performance is mainly attributed to better organic coverage and contact with an n-type SiNW surface.

Performance enhancement of blue light-emitting diodes without an electron-blocking layer by using special designed p-type doped InGaN barriers.

In this study, the characteristics of the nitride-based blue light-emitting diode (LED) without an electron-blocking layer (EBL) are analyzed numerically. The emission spectra, carrier concentrations in the quantum wells (QWs), energy band diagrams, electrostatic fields, and internal quantum efficiency (IQE) are investigated. The simulation results indicate that the LED without an EBL has a better hole-injection efficiency and smaller electrostatic fields in its active region over the conventional LED with an AlGaN EBL. The simulation results also show that the LED without an EBL has severe efficiency droop. However, when the special designed p-type doped InGaN QW barriers are used, the efficiency droop is markedly improved and the electroluminescence (EL) emission intensity is greatly enhanced which is due to the improvement of the hole uniformity in the active region and small electron leakage.