Investigation of reactive ion etching of dielectrics and Si in CHF₃/O₂ or CHF₃/Ar for photovoltaic applications

Using a combination of etch rate, photoconductance, and deep level transient spectroscopy(DLTS) measurements, the authors have investigated the use of reactive ion etching (RIE) of dielectrics and Si in CHF₃∕O₂ and CHF₃∕Arplasmas for photovoltaic applications. The radio frequency power (rf-power) and gas flow rate dependencies have shown that the addition of either O₂ or Ar to CHF₃ can be used effectively to change the etch selectivity between SiO₂ and Si₃N₄. The effective carrier lifetime of samples degraded upon exposure to a CHF₃-based plasma, reflecting the introduction of recombination centers in the near-surface region. The extent of minority carrier lifetime degradation was similar in both types of plasmas, suggesting that the same defects were responsible for the increased recombination. However, the rf-power dependence of lifetime degradation in n- and p-type Si was different. Moreover, the lifetime degradation did not exhibit a linear rf-power dependence, suggesting that primary defects were not the dominant recombination centers responsible for the decrease in lifetime. Indeed, DLTS measurements have shown that secondary defects were formed in samples exposed to the plasma after annealing at 400°C, the temperature at which a SiN:H layer is deposited on samples to passivate their surfaces. The minority carrier lifetime degradation in RIE processed samples could be partially avoided using post-RIE chemical treatments.The authors would like to thank the Australian Research Council for financial support

Electrical characterization of p-GaAs epilayers disordered by doped spin-on-glass

Impurity-free disordering (IFD) of uniformly dopedp‐GaAsepitaxial layers was achieved using either undoped or doped (Ga or P) spin-on-glass (SOG) in conjunction with rapid thermal annealing in the temperature range from 800to925°C. Capacitance-voltage measurements showed a pronounced increase in the doping concentration (NA) in the near-surface region of the layers disordered using both undoped and P:SOG. The increase in NA showed an Arrhenius-like dependence on the inverse of annealing temperature. On the other hand, NA did not change significantly for Ga-doped SOG. These changes can be explained by the relative injection of excess gallium vacancies (VGa) during IFD of p‐GaAs by the different SOG layers. Deep-level transient spectroscopy showed a corresponding increase in the concentration of a defect HA (EV+0.39eV), which can be attributed to Cu, in the undoped and P:SOG disordered p‐GaAs layers, but not in the epilayers disordered by Ga:SOG. We have explained the increase in free carrier concentration by the segregation of Zn atoms towards the surface during the injection of VGa. The redistribution of Zn during disordering of buried marker layers in GaAs and Al₀.₆Ga₀.₄As using either undoped or Ga-doped SOG was verified by secondary-ion mass spectrometry.One of the authors P. N. K. D.d acknowledges the financial support of the Australian Research Council. A second sF. D. A.d is grateful to the National Research Foundation, South Africa, for its financial support

Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation

Advance care planning uptake among patients with severe lung disease: A randomised patient preference trial of a nurse-led, facilitated advance care planning intervention

Objective Advance care planning (ACP) clarifies goals for future care if a patient becomes unable to communicate their own preferences. However, ACP uptake is low, with discussions often occurring late. This study assessed whether a systematic nurse-led ACP intervention increases ACP in patients with advanced respiratory disease. Design A multicentre open-label randomised controlled trial with preference arm. Setting Metropolitan teaching hospital and a rural healthcare network. Participants 149 participants with respiratory malignancy, chronic obstructive pulmonary disease or interstitial lung disease. Intervention Nurse facilitators offered facilitated ACP discussions, prompted further discussions with doctors and loved ones, and assisted participants to appoint a substitute medical decision-maker (SDM) and complete an advance directive (AD). Outcome measures The primary measure was formal (AD or SDM) or informal (discussion with doctor) ACP uptake assessed by self-report (6 months) and medical notes audit. Secondary measures were the factors predicting baseline readiness to undertake ACP, and factors predicting postintervention ACP uptake in the intervention arm. Results At 6 months, formal ACP uptake was significantly higher (p<0.001) in the intervention arm (54/106, 51%), compared with usual care (6/43, 14%). ACP discussions with doctors were also significantly higher (p<0.005) in the intervention arm (76/106, 72%) compared with usual care (20/43, 47%). Those with a strong preference for the intervention were more likely to complete formal ACP documents than those randomly allocated. Increased symptom burden and preference for the intervention predicted later ACP uptake. Social support was positively associated with ACP discussion with loved ones, but negatively associated with discussion with doctors. Conclusions Nurse-led facilitated ACP is acceptable to patients with advanced respiratory disease and effective in increasing ACP discussions and completion of formal documents. Awareness of symptom burden, readiness to engage in ACP and relevant psychosocial factors may facilitate effective tailoring of ACP interventions and achieve greater uptake. Trial registration number ACTRN12614000255684. © Published by the BMJ Publishing Group Limite

Distinction between the Poole-Frenkel and tunneling models of electric field-stimulated carrier emission from deep levels in semiconductors

The enhancement of the emission rate of charge carriers from deep-level defects in electric field is routinely used to determine the charge state of the defects. However, only a limited number of defects can be satisfactorily described by the Poole-Frenkel theory. An electric field dependence different from that expected from the Poole-Frenkel theory has been repeatedly reported in the literature, and no unambiguous identification of the charge state of the defect could be made. In this article, the electric field dependencies of emission of carriers from DX centers in AlxGa1-xAs:Te, Cu pairs in silicon, and Ge:Hg have been studied applying static and terahertz electric fields, and analyzed by using the models of Poole-Frenkel and phonon assisted tunneling. It is shown that phonon assisted tunneling and Poole-Frenkel emission are two competitive mechanisms of enhancement of emission of carriers, and their relative contribution is determined by the charge state of the defect and by the electric-field strength. At high-electric field strengths carrier emission is dominated by tunneling independently of the charge state of the impurity. For neutral impurities, where Poole-Frenkel lowering of the emission barrier does not occur, the phonon assisted tunneling model describes well the experimental data also in the low-field region. For charged impurities the transition from phonon assisted tunneling at high fields to Poole-Frenkel effect at low fields can be traced back. It is suggested that the Poole-Frenkel and tunneling models can be distinguished by plotting logarithm of the emission rate against the square root or against the square of the electric field, respectively. This analysis enables one to unambiguously determine the charge state of a deep-level defect

Electrical characterization of 1.8 MeV proton-bombarded ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation

Comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

A systematic investigation to check the quality of Pd Schottky contacts deposited on ZnO has been performed on electron beam (e-beam) deposited and resistively/thermally evaporated samples using current-voltage, IV, and conventional deep level transient spectroscopy (DLTS) measurements. Room temperature IV measurements reveal the dominance of pure thermionic emission on the resistively evaporated contacts, while the e-beam deposited contacts show the dominance of generation recombination at low voltages,<0.30 V, and the dominance of pure thermionic emission at high voltages, greater than 0.30 V. The resistively evaporated contacts have very low reverse currents of the order of 10 10 A at a reverse voltage of 1.0 V whereas the e-beam deposited contacts have reverse currents of the order of 10 6 A at 1.0 V. Average ideality factors have been determined as (1.4360.01) and (1.6660.02) for the resistively evaporated contacts and e-beam deposited contacts, respectively. The IV barrier heights have been calculated as (0.72160.002) eV and (0.62460.005) eV for the resistively evaporated and e-beam deposited contacts, respectively. Conventional DLTS measurements reveal the presence of three prominent defects in both the resistive and e-beam contacts. Two extra peaks with energy levels of 0.60 and 0.81 eV below the conduction band minimum have been observed in the e-beam deposited contacts. These have been explained as contributing to the generation recombination current that dominates at low voltages and high leakage currents. Based on the reverse current at 1.0 V, the degree of rectification, the dominant current transport mechanism and the observed defects, we conclude that the resistive evaporation technique yields better quality Schottky contacts for use in solar cells and ultraviolet detectors compared to the e-beam deposition technique. The 0.60 eV has been identified as possibly related to the unoccupied level for the doubly charged oxygen vacancy, Vо2+.The National Research Foundation of South Africahttp://dx.doi.org/10.1063/1.3658027nf201

Ultra violet sensors based on nanostructured ZnO spheres in network of nanowires: a novel approach

The ZnO nanostructures consisting of micro spheres in a network of nano wires were synthesized by direct vapor phase method. X-ray Photoelectron Spectroscopy measurements were carried out to understand the chemical nature of the sample. ZnO nanostructures exhibited band edge luminescence at 383 nm. The nanostructure based ZnO thin films were used to fabricate UV sensors. The photoresponse measurements were carried out and the responsivity was measured to be 50 mA W−1. The rise and decay time measurements were also measured

The Improving Rural Cancer Outcomes Trial: a cluster-randomised controlled trial of a complex intervention to reduce time to diagnosis in rural cancer patients in Western Australia.

BACKGROUND: Rural Australians have poorer survival for most common cancers, due partially to later diagnosis. Internationally, several initiatives to improve cancer outcomes have focused on earlier presentation to healthcare and timely diagnosis. We aimed to measure the effect of community-based symptom awareness and general practice-based educational interventions on the time to diagnosis in rural patients presenting with breast, prostate, colorectal or lung cancer in Western Australia. METHODS: 2 × 2 factorial cluster randomised controlled trial. Community Intervention: cancer symptom awareness campaign tailored for rural Australians. GP intervention: resource card with symptom risk assessment charts and local cancer referral pathways implemented through multiple academic detailing visits. Trial Area A received the community symptom awareness and Trial Area B acted as the community campaign control region. Within both Trial Areas general practices were randomised to the GP intervention or control. PRIMARY OUTCOME: total diagnostic interval (TDI). RESULTS: 1358 people with incident breast, prostate, colorectal or lung cancer were recruited. There were no significant differences in the median or ln mean TDI at either intervention level (community intervention vs control: median TDI 107.5 vs 92 days; ln mean difference 0.08 95% CI -0.06-0.23 P=0.27; GP intervention vs control: median TDI 97 vs 96.5 days; ln mean difference 0.004 95% CI -0.18-0.19 P=0.99). There were no significant differences in the TDI when analysed by factorial design, tumour group or sub-intervals of the TDI. CONCLUSIONS: This is the largest trial to test the effect of community campaign or GP interventions on timeliness of cancer diagnosis. We found no effect of either intervention. This may reflect limited dose of the interventions, or the limited duration of follow-up. Alternatively, these interventions do not have a measurable effect on time to cancer diagnosis