New photoluminescence lines in Vanadium doped GaAs grown by MOVPE
We examined the electrical and optical properties of vanadium-doped GaAs grown by metalorganic vapour phase epitaxy using vanadium tetrachloride (VCl4) as a novel dopant source. Samples with various vanadium incorporations were investigated. All samples were n type. The electron concentration dependence on the VCl4 flow rate was established. At 15 K, by comparison with undoped layers grown in the same conditions, photoluminescence spectra of V-doped exhibited three new emission bands: at 1.41, 1 and 0.72 eV. The 1 and 0.72 eV band emissions were attributed to V 2þ and V 3þ intracenter emission, while the 1.41 eV band was suggested to be a donor-bound transition. The identity of the donor is tentatively attributed to a donor complex that associates vanadium to an arsenic vacancy. From Hall effect as function of temperature, the donor ionisation energy was estimated to be about 102 ^ 5 meV. q 2003 Elsevier Science Ltd. All rights reserved.
Photoluminescence Study of Defects in GaAs Formed by Annealing in an H2 Gas Flow
GaAs crystals were annealed in an H2 gas flow and the degraded layer formed on the surface by annealing has been investigated by a photoluminescence measurement. The origin of the defects, in particular an emission at 890 nm, formed by annealing has also been investigated with the aid of the liquid phase epitaxy technique. The degradation of the surface is governed by self-diffusion of As vacancies. The degraded layer depth increases in proportion to the square root of the heating time, whose rate depends on carrier concentrations in the crystals. As the crystals are annealed in an H2 gas flow, new emission band at 890 nm grows drastically. It is concluded that the band is due to electron transitions from a shallow donor to an As vacancy acceptor.
Public Hospitals : Options for Reform through Public-Private Partnerships
Globally, health expenditures rose from an average of 3 percent of GDP in 1950 to 8 percent (US$3 trillion) in 1999 (WHO 2000). The increase in spending has been driven by rising income, changing demographic and epidemiological trends, and costly new pharmaceuticals and technology. Although technology is allowing a shift to outpatient care, hospitals still account for 30–50 percent of health expenditures. Public funding has not kept pace with the growth in spending. Much of the increase has been financed from private sources (out-ofpocket payments and private insurance), while the share funded publicly (by tax revenue and national insurance) declined by 6 percent between 1977 and 1997. Constraints on public funding, combined with rising costs, have forced public hospitals to cut costs wherever possible while still endeavoring to guarantee universal (and often free) access to public patients.1 Governments have used different strategies to address these problems, such as shifting financing from general tax revenue to payroll-financed national health insurance, narrowing the basic package of services available to all citizens, linking hospital funding to outputs and efficiency, amalgamating hospitals into networks, increasing autonomy and incentives for management, and reducing the number of hospital beds. Some governments have also turned to public-private partnerships to bring private sector efficiency into public hospitals.