Showing papers by "S.E. Holland published in 2006"

Silicon Detectors for Low Energy Particle Detection

Abstract: Silicon detectors with very thin entrance contacts have been fabricated for use in the IMPACT SupraThermal Electron (STE) instrument on the STEREO mission and for the solid state telescopes on the THEMIS mission. The silicon diode detectors were fabricated using a 200 Aring thick phosphorous doped polysilicon layer that formed the thin entrance window. A 200 Aring thick aluminum layer was deposited on top of the polysilicon in order to reduce their response to stray light. Energy loss in the entrance contact was about 350 eV for electrons and about 2.3 keV for protons. The highest detector yield was obtained using a process in which the thick polysilicon gettering layer was removed by chemical etching rather than chemical mechanical polishing.

Reduced Charge Diffusion in Thick, Fully Depleted CCDs With Enhanced Red Sensitivity

Abstract: Lateral charge diffusion in charge-coupled devices (CCDs) dominates the device point-spread function (PSF), which can affect both image quality and spectroscopic resolution. We present new data and theoretical interpretations for lateral charge diffusion in thick, fully depleted CCDs developed at Lawrence Berkeley National Laboratory (LBNL). Because they can be overdepleted, the LBNL devices have no field-free region and diffusion is controlled through the application of an external bias voltage. Recent improvements in CCD design at LBNL allow the application of bias voltages exceeding 200 V. We give results for a 3512times3512 format, 10.5 mum pixel back-illuminated p-channel CCD developed for the SuperNova/Acceleration Probe (SNAP), a proposed satellite-based experiment designed to study dark energy. Lateral charge diffusion, which is well described by a symmetric two-dimensional (2-D) Gaussian function, was measured at substrate bias voltages between 3 and 115 V. At a bias voltage of 115 V, we measure a root-mean square (rms) diffusion of 3.7plusmn0.2mum. Lateral charge diffusion in LBNL CCDs will meet the SNAP requirements

Ccd development progress at lawrence berkeley national laboratory

Abstract: Author(s): Kolbe, W.F.; Holland, S.E.; Bebek, C.J. | Abstract: P-channel CCD imagers, 200-300um thick, fully depleted, and back-illuminat ed are being developed for scientific applications including ground- and space-based astronomy and x-ray detection. These thick devices have extended IR response, good point-spread function (PSF) and excellent radiation tolerance. Initially, these CCDs were made in-house at LBNL using 100 mm diameter wafers. Fabrication on high-resistivity 150 mm wafers is now proceeding according to a model in which the wafers are first processed at DALSA Semiconductor up to the Al contact mask step. They are then thinned and the rest of the processing is done in small batches at LBNL. Alternative approaches are also discussed. In addition we have implemented designs that permit high-voltage biasing to further improve the PSF. With these designs, operation of 200 um thick C CDs at 100 V or more bias with excellent PSF is practical.

Radiation Tolerance of High-Resistivity LBNL CCDs

Abstract: Thick, fully-depleted p-channel charge-coupled devices (CCDs) have been developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have several advantages over conventional n-channel CCDs, including enhanced quantum efficiency and reduced fringing at near-infrared wavelengths, a small point spread function, and improved radiation tolerance. Here we report results from the irradiation of CCDs with 12.5 and 55 MeV protons at the LBNL 88-Inch Cyclotron. These studies indicate that the CCDs still perform well after irradiation, even in the parameters in which significant degradation is expected: charge transfer efficiency, dark current, and isolated hot pixels. As expected, the radiation tolerance of the LBNL CCDs is significantly improved over conventional n-channel CCDs currently employed in space-based telescopes such as the Hubble Space Telescope (HST).

Delta-Doped High Purity Silicon UV-NIR CCDs with High QE and Low Dark Current

Abstract: Delta doping process was developed on p-channel CCDs for MIDEX-Orion and JDEM/SNAP and was applied to large format (2k x4k) CCDs. Delta doping is applied to fully-fabricated CCDs (complete with Al metallization). High QE and low dark current is demonstrated with delta doped p-channel CCDs. In-house AR coating is demonstrated. Advantages include: Delta doping enables high QE and stability across the entire spectral range attainable with silicon. Delta doping is a low temperature process and is compatible with fully-fabricated detector arrays. Same base device for Orion two channels. High radiation tolerance and no thinning requirements of high purity p-channel. CCDs are additional advantages.