Shallow and Deep States of Beryllium Acceptor in GaN: Why Photoluminescence Experiments Do Not Reveal Small Polarons for Defects in Semiconductors

Currently, only one shallow acceptor (Mg) has been discovered in GaN. Here, using photoluminescence (PL) measurements combined with hybrid density functional theory, we demonstrate that a shallow effective-mass state also exists for the Be_{Ga} acceptor. A PL band with a maximum at 3.38 eV reveals a shallow Be_{Ga} acceptor level at 113±5  meV above the valence band, which is the lowest value among any dopants in GaN reported to date. Calculations suggest that the Be_{Ga} is a dual-nature acceptor with the "bright" shallow state responsible for the 3.38 eV PL band, and the "dark," strongly localized small polaronic state with a significantly lower hole capture efficiency.

Determination of the concentration of impurities in GaN from photoluminescence and secondary-ion mass spectrometry

Photoluminescence (PL) was used to estimate the concentration of carbon in GaN grown by hydride vapor phase epitaxy (HVPE). The PL data were compared with profiles of the impurities obtained from secondary ion mass spectrometry (SIMS) measurements. Comparison of PL and SIMS data has revealed that apparently high concentrations of C and O at depths up to 1 µm in SIMS profiles do not represent depth distributions of these species in the GaN matrix but are rather caused by post-growth surface contamination and knocking-in impurity species from the surface. In particular, PL analysis supplemented by reactive ion etching up to the depth of 400 nm indicates that the concentration of carbon in nitrogen sites is below 2-5 × 10¹⁵ cm^-3 at any depth of GaN samples grown by HVPE. We demonstrate that PL is a very sensitive and reliable tool to determine the concentrations of impurities in the GaN matrix.

Acute viral hepatitis (C - genotype 6a and B) acquired during kidney transplantation by two patients and review of the literature

Two patients were contaminated by hepatitis during kidney transplantation from unrelated living donors, performed abroad in 2006. One patient died from fulminant hepatitis C (the first case of virus genotype 6a diagnosed in Israel) 2 months after transplantation and the other developed acute hepatitis B with YMDD to YVDD mutation necessitating life-long antiviral therapy. The dilemma of antiviral therapy in transplant recipients is discussed in this paper. Patients awaiting kidney transplantation by far outnumber the kidneys available for cadaver transplantation. International trade with living non-related kidneys has therefore become common. Comorbid conditions, although significant, are often ignored. After transplantation, the first patient presented with a picture of fulminant hepatitis C; immunosuppressive medication was tapered rapidly. This patient subsequently died from hepatic failure. The patient with active hepatitis B with YVDD mutation is receiving ongoing treatment by lamivudine and adefovir.

Surveillance of chronic haemodialysis-associated infections in southern Israel

During a 12-month surveillance period, haemodialysis (HD) patients in southern Israel were categorised according to the type of vascular access site (VAS), i.e., arteriovenous (AV) fistula, synthetic AV graft, and cuffed or non-cuffed vascular catheters. Endpoints, expressed as cases/100 patient-months, were: incidence of hospital admission; antibiotic therapy; bloodstream infection (BSI); and VAS infection. These were compared to Centers for Disease Control (CDC) surveillance data, overall and by VAS type. In total, 2568 patient-months were analysed. The VAS distribution differed significantly from CDC data for fistulas (72% vs. 31%), grafts (12% vs. 41%), cuffed catheters (11% vs. 25%) and non-cuffed catheters (5% vs. 3%) (p < 0.0001 in all cases). Of 151 admissions, 32% resulted from infection, for which 112 antibiotic courses (22% vancomycin) were given. There were 16 BSIs, three involving resistant strains. The incidences of admission, antibiotic therapy, BSI and VAS infection were significantly lower overall, compared to CDC rates, as were most VAS-specific endpoints. These differences may be explained by VAS type distribution, although other factors may also be involved. Reporting regional or national surveillance data may allow a standardised comparison of the incidence of HD-associated infections.

Increased coagulation factor levels leading to allograft renal vein thrombosis

A patient with end-stage kidney disease is described, who lost his renal allograft in the early post-transplant period due to allograft renal vein thrombosis. Prior to transplantation, he had been treated by hemodialysis and lost several vascular accesses because of thrombosis. A search for potential thrombophilic factors disclosed a unique combination of increased clotting factor levels, i.e. FVIII, FIX, FXI and homocysteine. More common hereditary and acquired hypercoagulability factors have been excluded in this patient. While clotting factor deficiencies are well known causes of hemophilia, their levels should also be measured in the workup of transplant candidates with a history of multiple vascular access thrombosis.