We describe research and development efforts directed towards the production of 4 k × 4 k, 15 µm-pixel, fully depleted CCDs for the Dark Energy Spectroscopic Instrument (DESI). The requirements for DESI include the spectroscopic characterization of large numbers of faint galaxies at high redshift. The identification of the type and the determination of the redshift of the targeted galaxies require the use of thick, fully depleted CCDs with high quantum efficiency at near-infrared wavelengths. We describe our work to improve the CCD performance in terms of quantum efficiency and read noise. We also discuss efforts to reduce the level of image-distortion effects that have been observed on previous CCDs that are due to resistivity striations in the starting silicon and periodic errors in the photomasks used to produce the CCDs.
We describe the design and optimization of low-noise, single-stage output amplifiers for p-channel charge-coupled devices (CCDs) used for scientific applications in astronomy and other fields. The CCDs are fabricated on highresistivity, 4000-5000 Ω-cm, n-type silicon substrates. Single-stage amplifiers with different output structure designs and technologies have been characterized. The standard output amplifier is designed with an n + polysilicon gate that has a metal connection to the sense node. In an effort to lower the output amplifier readout noise by minimizing the capacitance seen at the sense node, buried-contact technology has been investigated. In this case, the output transistor has a p + polysilicon gate that connects directly to the p + sense node. Output structures with buried-contact areas as small as 2 µm × 2 µm are characterized. In addition, the geometry of the source-follower transistor was varied, and we report test results on the conversion gain and noise of the various amplifier structures. By use of buried-contact technology, better amplifier geometry, optimization of the amplifier biases and improvements in the test electronics design, we obtain a 45% reduction in noise, corresponding to 1.7 e − rms at 70 kpixels/sec.
XANES and EXAFS studies have been carried out on Fe doped ZnO thin films having different Fe doping concentration ranging from 1% to 10% and the observed ferromagnetism in the samples is explained in the light of XANES and EXAFS observations.
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