Impact of dopant-induced band tails on optical spectra, charge carrier transport, and dynamics in single-crystal CdTe.

Cadmium telluride (CdTe) semiconductors are used in thin-film photovoltaics, detectors, and other optoelectronic applications. For all technologies, higher efficiency and sensitivity are achieved with reduced charge carrier recombination. In this study, we use state-of-the-art CdTe single crystals and electro-optical measurements to develop a detailed understanding of recombination rate dependence on excitation and temperature in CdTe. We study recombination and carrier dynamics in high-resistivity (undoped) and arsenic (As)-doped CdTe by employing absorption, the Hall effect, time-resolved photoluminescence, and pump-probe in the 80-600 K temperature range. We report extraordinarily long lifetimes (30 µs) at low temperatures in bulk undoped CdTe. Temperature dependencies of carrier density and mobility reveal ionization of the main acceptors and donors as well as dominant scattering by ionized impurities. We also distinguish different recombination defects. In particular, shallow AsTe and deep VCd-AsCd acceptors were responsible for p-type conductivity. AX donors were responsible for electron capture, while nonradiative recombination centers (VCd-AsTe, As2 precipitates), and native defects (VCd-TeCd) were found to be dominant in p-type and n-type CdTe, respectively. Bimolecular and surface recombination rate temperature dependencies were also revealed, with bimolecular coefficient T-3/2 temperature dependence and 170 meV effective surface barrier, leading to an increase in surface recombination velocity at high temperatures and excitations. The results of this study allowed us to conclude that enhanced crucible rotation growth of As-doped CdTe is advantageous to As activation, leading to longer lifetimes and larger mobilities and open-circuit voltages due to lower absorption and trapping.

Incident wavelength and polarization dependence of spectral shifts in ß-Ga2O3 UV photoluminescence.

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped ß-Ga2O3 bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed between E||b and E||c, while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70-160 meV, which is supported by the calculations.

Zn Vacancy Formation Energy and Diffusion Coefficient of CVT ZnO Crystals in the Sub-Surface Micron Region.

By using positron annihilation spectroscopy methods, we have experimentally demonstrated the creation of isolated zinc vacancy concentrations >1020 cm-3 in chemical vapor transport (CVT)-grown ZnO bulk single crystals. X-ray diffraction ω-rocking curve (XRC) shows the good quality of ZnO single crystal with (110) orientation. The depth analysis of Auger electron spectroscopy indicates the atomic concentrations of Zn and O are almost stoichiometric and constant throughout the measurement. Boltzmann statistics are applied to calculate the zinc vacancy formation energies (Ef) of ~1.3-1.52 eV in the sub-surface micron region. We have also applied Fick's 2nd law to calculate the zinc diffusion coefficient to be ~1.07 × 10-14 cm2/s at 1100 °C. The zinc vacancies began annealing out at 300 °C and, by heating in the air, were completely annealed out at 700 °C.

p-type doping efficiency in CdTe: Influence of second phase formation.

Cadmium telluride (CdTe) high purity, bulk, crystal ingots doped with phosphorus were grown by the vertical Bridgman melt growth technique to understand and improve dopant solubility and activation. Large net carrier densities have been reproducibly obtained from as-grown ingots, indicating successful incorporation of dopants into the lattice. However, net carrier density values are orders of magnitude lower than the solubility of P in CdTe as reported in literature, 1018/cm3 to 1019/cm3 [J. H. Greenberg, J. Cryst. Growth 161, 1-11 (1996) and R. B. Hall and H. H. Woodbury, J. Appl. Phys. 39(12), 5361-5365 (1968)], despite comparable starting charge dopant densities. Growth conditions, such as melt stoichiometry and post growth cooling, are shown to have significant impacts on dopant solubility. This study demonstrates that a significant portion of the dopant becomes incorporated into second phase defects as compounds of cadmium and phosphorous, such as cadmium phosphide, which inhibits dopant incorporation into the lattice and limits maximum attainable net carrier density in bulk crystals. Here, we present an extensive study on the characteristics of these second phase defects in relation to their composition and formation kinetics while providing a pathway to minimize their formation and enhance solubility.

Self-compensation in arsenic doping of CdTe.

Efficient p-type doping in CdTe has remained a critical challenge for decades, limiting the performance of CdTe-based semiconductor devices. Arsenic is a promising p-type dopant; however, reproducible doping with high concentration is difficult and carrier lifetime is low. We systematically studied defect structures in As-doped CdTe using high-purity single crystal wafers to investigate the mechanisms that limit p-type doping. Two As-doped CdTe with varying acceptor density and two undoped CdTe were grown in Cd-rich and Te-rich environments. The defect structures were investigated by thermoelectric-effect spectroscopy (TEES), and first-principles calculations were used for identifying and assigning the experimentally observed defects. Measurements revealed activation of As is very low in both As-doped samples with very short lifetimes indicating strong compensation and the presence of significant carrier trapping defects. Defect studies suggest two acceptors and one donor level were introduced by As doping with activation energies at ~88 meV, ~293 meV and ~377 meV. In particular, the peak shown at ~162 K in the TEES spectra is very prominent in both As-doped samples, indicating a signature of AX-center donors. The AX-centers are believed to be responsible for most of the compensation because of their low formation energy and very prominent peak intensity in TEES spectra.

Long-term outcomes for primary glomerulonephritis: New Zealand Glomerulonephritis Study.

AIMS: Due to the paucity of studies focusing on primary glomerulonephritis, the second commonest cause of end-stage-kidney-disease in most of the developed world, we sought to review outcomes of these renal pathologies. METHODS: We reviewed renal outcomes and mortality for primary glomerulonephritis patients enrolled in the New Zealand Glomerulonephritis Study between 1972 and 1983. RESULTS: There were 765 patients with median follow-up of 30 years (range 0.1-42 years). They were predominantly New Zealand European, male and hypertensive. Poor renal outcomes and increased mortality were associated with hypertension, heavy proteinuria, impaired renal function and older age at diagnosis. Ethnicity was not significantly associated with progression to end-stage-kidney-disease although NZ Maori patients were at significantly increased risk of death. Patients with rapidly progressive glomerulonephritis had the highest risk of reaching end-stage-kidney-disease while the cumulative incidence of end-stage-kidney-disease was 20% and 30% for those with immunoglobulin-A nephropathy and membranous nephropathy respectively. Mortality risk was high for patients with rapidly progressive glomerulonephritis and anti-glomerular basement membrane disease. The era of diagnosis did not have much effect on outcomes except for patients with focal segmental glomerulosclerosis or immunoglobulin A nephropathy but this could be type II error. CONCLUSION: We report one of the longest follow-up studies on biopsy-proven glomerulonephritides. Age, hypertension, and severity of chronic kidney disease at diagnosis were strong predictors of the development of end-stage-kidney-disease and death. The specific renal pathology had a profound impact upon prognosis and therefore should continue to drive efforts to find targeted therapeutic options for these glomerulonephritides.

Survival on home dialysis in New Zealand.

BACKGROUND: New Zealand (NZ) has a high prevalence of both peritoneal dialysis (PD) and home haemodialysis (HD) relative to other countries, and probably less selection bias. We aimed to determine if home dialysis associates with better survival than facility HD by simultaneous comparisons of the three modalities. METHODS: We analysed survival by time-varying dialysis modality in New Zealanders over a 15-year period to 31-Dec-2011, adjusting for patient co-morbidity by Cox proportional hazards multivariate regression. RESULTS: We modelled 6,419 patients with 3,254 deaths over 20,042 patient-years of follow-up. Patients treated with PD and facility HD are similar; those on home HD are younger and healthier. Compared to facility HD, home dialysis (as a unified category) associates with an overall 13% lower mortality risk. Home HD associates with a 52% lower mortality risk. PD associates with a 20% lower mortality risk in the early period (<3 years) that is offset by a 33% greater mortality risk in the late period (>3 years), with no overall net effect. There was effect modification and less observable benefit associated with PD in those with diabetes mellitus, co-morbidity, and in NZ Maori and Pacific People. There was no effect modification by age or by era. CONCLUSION: Our study supports the culture of home dialysis in NZ, and suggests that the extent and duration of survival benefit associated with early PD may be greater than appreciated. We are planning further analyses to exclude residual confounding from unmeasured co-morbidity and other sociodemographic factors using database linkage to NZ government datasets. Finally, our results suggest further research into the practice of PD in NZ Maori and Pacific People, as well as definitive study to determine the best timing for switching from PD in the late phase.

IgA nephropathy in identical twins: an excellent donor and recipient outcome 11 years after transplantation.

We present a case of IgA nephropathy (IgAN) in monozygotic twins with excellent donor and recipient outcome 11 years after transplantation. The recipient developed IgAN at 26 years and progressed to end-stage renal failure 10 years later. His identical twin who had hypertension, intermittent microscopic haematuria and positive IgA immunofluorescence on biopsy became his donor. Eleven years following transplant, in the absence of immunosuppression, the recipient has stable graft function [estimated glomerular filtration rate (eGFR) 47 mL/min/1.73 m(2), Modification of Diet in Renal Disease (MDRD)], controlled hypertension on two medications and minor microscopic haematuria. The donor has good renal function (eGFR 51 mL/min/1.73 m(2), MDRD), controlled hypertension on one medication and normal urine.

Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomerulosclerosis.

Focal and segmental glomerulosclerosis (FSGS) is a major cause of end-stage kidney disease. Recent advances in molecular genetics show that defects in the podocyte play a major role in its pathogenesis and mutations in inverted formin 2 (INF2) cause autosomal dominant FSGS. In order to delineate the role of INF2 mutations in familial and sporadic FSGS, we sought to identify variants in a large cohort of patients with FSGS. A secondary objective was to define an approach for genetic screening in families with autosomal dominant disease. A total of 248 individuals were identified with FSGS, of whom 31 had idiopathic disease. The remaining patients clustered into 64 families encompassing 15 from autosomal recessive and 49 from autosomal dominant kindreds. There were missense mutations in 8 of the 49 families with autosomal dominant disease. Three of the detected variants were novel and all mutations were confined to exon 4 of INF2, a regulatory region responsible for 90% of all changes reported in FSGS due to INF2 mutations. Thus, in our series, INF2 mutations were responsible for 16% of all cases of autosomal dominant FSGS, with these mutations clustered in exon 4. Hence, screening for these mutations may represent a rapid, non-invasive and cost-effective method for the diagnosis of autosomal dominant FSGS.

First and subsequent nonmelanoma skin cancers: incidence and predictors in a population of New Zealand renal transplant recipients.

BACKGROUND: Renal transplant recipients (RTRs) have an increased risk of developing nonmelanoma skin cancers (NMSCs). The aims of this study were to determine the incidence and subsequent history of NMSCs in RTRs, together with risk factors. METHODS: All patients transplanted between July 1972 and March 2007, and followed up at Christchurch Hospital, New Zealand, were studied. Immunosuppression regimens were mostly prednisone, azathioprine, cyclosporine and prednisone, mycophenolate mofetil, cyclosporine since 1998. RESULTS: Of 384 RTRs, 96 developed at least one NMSC. The median time to first NMSC was 18.3 years (95% CI 14.2, 22.9) from transplant, as estimated by survival analysis. Individual predictors of first NMSC in RTRs were older age at first transplant (P < 0.0001), male sex (P = 0.006) and initial immunosuppression regimen (P = 0.001); only age (P < 0.0001) and male gender (P = 0.003) were significant predictors in a joint model. The mean rate of subsequent NMSCs was 1.67 per year (95% CI = 1.32, 2.11). Older age at first renal transplant (P = 0.009) or at discovery of the first NMSC (P = 0.01) was associated with a higher annual rate of new NMSC following the discovery of the first NMSC. The median survival time to a second NMSC was 2.2 years (CI 1.4, 3.0). Fourteen patients died of metastatic squamous cell carcinoma (15% case fatality). CONCLUSIONS: NMSCs are a major health issue for RTRs, especially in older males. Once RTRs have developed their first NMSC, ongoing surveillance and prompt treatment are essential.

ZnTe6O13, a new ZnO-TeO2 phase.

Our investigations into the ZnO-TeO(2) system have produced a new phase, zinc(II) hexatellurium(IV) tridecaoxide, ZnTe(6)O(13), with trigonal (R3) symmetry, synthesized by repeated heating and cooling to a maximum temperature of 1053 K. The asymmetric unit consists of a Zn atom coordinated in a distorted octahedral fashion by two unique tellurium(IV) oxide units that form trigonal-bipyramidal TeO(4) and TeO(3+1) corner- and edge-shared polyhedra. Except for the Zn and an O atom, which occupy 6c positions, all atoms occupy 18f general positions.

Physico-chemical characterization of nanofiltration membranes.

This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly.

The pharmacokinetics and tolerability of oseltamivir suspension in patients on haemodialysis and continuous ambulatory peritoneal dialysis.

BACKGROUND: Oseltamivir dose reduction is recommended for patients with end-stage renal disease (ESRD). However, dosing recommendations are not available for treatment or prophylaxis of influenza in these patients. This study assessed the pharmacokinetics and tolerability of oseltamivir in ESRD patients undergoing maintenance haemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD). METHODS: In this open-label, multiple-dose study, patients received 30 mg oral oseltamivir suspension over 6.5 weeks. This dose was predicted to be suitable for ESRD patients based on a 2-compartment model. HD patients received 9 doses given 1 h after the completion of alternate HD sessions (three times a week). CAPD patients received 6 doses given once weekly after a dialysate exchange. The primary parameters were peak plasma concentration (C(max)) and the area under the curve (AUC) for oseltamivir and oseltamivir carboxylate. RESULTS: In HD patients, the C(max) for oseltamivir carboxylate after single and repeated dosing were 943 and 1120 ng/ml, respectively. The mean AUC(0-42) was 31 600 ng h/ml for days 1-5 and 38 200 ng h/ml for days 38-43. Similarly, in CAPD patients, mean C(max) after the first and sixth doses were 885 and 849 ng/ml, respectively. The mean AUC(0-48) values for days 1-6 and days 36-43 were 33 400 and 32 400 ng h/ml, respectively. Oseltamivir was well-tolerated in both the patient groups. CONCLUSIONS: A 30 mg dose of oseltamivir given once weekly in CAPD or after alternate sessions in HD patients provides sufficient exposure to oseltamivir carboxylate to allow safe and effective anti-influenza treatment and prophylaxis.

Future of home haemodialysis in Australia and New Zealand.

Maintenance haemodialysis (HD) was pioneered in Seattle and rapidly became home-based. When dialysis treatment began in Australia and New Zealand, home haemodialysis (HHD) became the predominant form of dialysis. When compared with in-centre conventional dialysis, HHD is associated with superior survival and quality of life and is cheaper. There is currently significant interest in increasing the frequency and duration of dialysis and in providing more flexible dialysis regimens for patients. If the likely benefits of these treatment changes are to be fully realized HHD and self care HD services will need to expand. Dialysis units in Australia and New Zealand are better equipped than most to respond to this challenge.

A mutation in the TRPC6 cation channel causes familial focal segmental glomerulosclerosis.

Focal and segmental glomerulosclerosis (FSGS) is a kidney disorder of unknown etiology, and up to 20% of patients on dialysis have been diagnosed with it. Here we show that a large family with hereditary FSGS carries a missense mutation in the TRPC6 gene on chromosome 11q, encoding the ion-channel protein transient receptor potential cation channel 6 (TRPC6). The proline-to-glutamine substitution at position 112, which occurs in a highly conserved region of the protein, enhances TRPC6-mediated calcium signals in response to agonists such as angiotensin II and appears to alter the intracellular distribution of TRPC6 protein. Previous work has emphasized the importance of cytoskeletal and structural proteins in proteinuric kidney diseases. Our findings suggest an alternative mechanism for the pathogenesis of glomerular disease.

Hypertension and survival in hemodialysis patients.

Hypertension is clearly an independent risk factor for cardiovascular (CV) events and death in the general population, but the relationship between blood pressure (BP) and survival in dialysis patients is less clear. In dialysis populations at lower risk of CV events, BP is directly related to survival, while in those with high risk, it has been difficult to show such an effect. The effects of cardiac disease complicate the relationship between BP and outcome. Retrospective studies of large cohorts, with high prevalence of CV disease, have shown a U-shaped relationship between both systolic and diastolic BP and outcome. These findings probably reflect a high prevalence of cardiac failure and thus high mortality associated with low BP (i.e., a so-called reverse causation). Pulse pressure (high systolic BP and low diastolic BP) predicts outcome in hypertensive dialysis patients. Whether this reflects advanced vessel wall disease or is an independent etiologically significant risk factor is unclear. However, the current uncertainties as to the exact relationship between BP and outcome in dialysis patients do not warrant complacency regarding the prevention and treatment of hypertension.

Long-term survival of arteriovenous fistulas in home hemodialysis patients.

BACKGROUND: We report the outcome of arteriovenous (AV) fistulas created and managed by a multidisciplinary team in patients on hemodialysis (HD) over 20 years. METHODS: We analyzed 432 AV fistulas in 301 home HD patients (12% diabetic; median age 47 years) followed for up to 161 months. Observed end points were spontaneous or surgical AV fistula closure, or construction of a new vascular anastomosis. Survival was analyzed for first and second AV fistulas and predictors of outcome for first AV fistulas. RESULTS: One vascular surgeon constructed 58% of AV fistulas. Three hundred sixty-seven AV fistulas were in the forearm, 64 at or above the elbow, and 1 in the thigh. Four hundred fourteen AV fistulas used in situ vessels, and 18 were autografts. Two hundred thirty-one anastomoses were side-to-side. Only five grafts were placed during this time. There were 131 second and subsequent AV fistulas in 76 patients, 79 (60%) of which required primary construction, and 52 used arterialized vessels from a previous AV fistula. The median time from formation to use for first and second AV fistula, respectively, was 2.39 (SE 0.35) and 3.2 (SE 1.9) months. Assisted survival from first use for first AV fistula was 90% at 1 year, 66% at 5 years, 84% at 1 year, and 72% at 2 years for second AV fistula. AV fistula survival from creation was superior for side-to-side anastomoses (P < 0.0001) and in men (P= 0.05). CONCLUSION: A multidisciplinary approach has been successful in providing durable AV fistulas for home HD for >95% of consecutive patients entering our program.

Effects of early and late intervention with epoetin alpha on left ventricular mass among patients with chronic kidney disease (stage 3 or 4): results of a randomized clinical trial.

It is not known whether prevention of anemia among patients with chronic kidney disease would affect the development or progression of left ventricular (LV) hypertrophy. A randomized controlled trial was performed with 155 patients with chronic kidney disease (creatinine clearance, 15 to 50 ml/min), with entry hemoglobin concentrations ([Hb]) of 110 to 120 g/L (female patients) or 110 to 130 g/L (male patients). Patients were monitored for 2 yr or until they required dialysis; the patients were randomized to receive epoetin alpha as necessary to maintain [Hb] between 120 and 130 g/L (group A) or between 90 and 100 g/L (group B). [Hb] increased for group A (from 112 +/- 9 to 121 +/- 14 g/L, mean +/- SD) and decreased for group B (from 112 +/- 8 to 108 +/- 13 g/L) (P < 0.001, group A versus group B). On an intent-to-treat analysis, the changes in LV mass index for the groups during the 2-yr period were not significantly different (2.5 +/- 20 g/m(2) for group A versus 4.5 +/- 20 g/m(2) for group B, P = NS). There was no significant difference between the groups in 2-yr mean unadjusted systolic BP (141 +/- 14 versus 138 +/- 13 mmHg) or diastolic BP (80 +/- 6 versus 79 +/- 7 mmHg). The decline in renal function in 2 yr, as assessed with nuclear estimations of GFR, also did not differ significantly between the groups (8 +/- 9 versus 6 +/- 8 ml/min per 1.73 m(2)). In conclusion, maintenance of [Hb] above 120 g/L, compared with 90 to 100 g/L, had similar effects on the LV mass index and did not clearly affect the development or progression of LV hypertrophy. The maintenance of [Hb] above 100 g/L for many patients in group B might have been attributable to the relative preservation of renal function.

Effects of long and short hemodialysis on endothelial function: a short-term study.

BACKGROUND: Endothelial dysfunction is common in end-stage renal disease and may contribute to the development of both hypertension and atherosclerosis. Long-slow hemodialysis (HD) has been associated with superior blood pressure control and fewer cardiovascular complications. We hypothesized that long dialysis times would improve endothelial function compared with shorter dialysis times. METHOD: Eight long-term hemodialysis patients, not on antihypertensive drugs and with no evidence of vascular disease, were studied in a three-way randomized crossover-controlled trial. Each received, for one week and in randomized sequence, four hours of HD (SD), eight hours of HD, and eight hours of HD using a smaller dialyzer and slower blood pump. The same post-dialysis target weights were used with each treatment. On the third day of each treatment endothelium-dependent (flow mediated) and independent glyceryl trinitrate (GTN) induced vasodilation were measured by forearm strain-gauge plethysmography, and von Willebrand (vW) antigen, plasma homocysteine (tHcy) and neurohormones were measured pre- and post-dialysis. RESULTS: Despite achieving target post-dialysis weights with all treatments, pre-dialysis weight tended higher on SD. Endothelial dependent vasodilation increased after all HD treatments but did not differ between them. Adrenomedullin, N-terminal brain natriuretic peptide and vW antigen increased similarly across all HD whereas atrial and C-type natriuretic peptide, and endothelin-1 decreased across dialysis and were higher with SD. Pre-dialysis plasma tHcy concentrations were 13% higher during SD treatment. CONCLUSION: Hemodialysis improved endothelial-dependent vasodilation but the effect was similar with all three HD treatments. Improved endothelial function might result in part from altered local hormone production (endothelin-1 and adrenomedullin). These data suggest that increasing dialysis time is unlikely, in the short-term, to significantly improve endothelial function in patients with end-stage renal disease, but longer term studies are needed.