Jorge Jiménez

Schottky barrier heights of Pt and Ir silicides formed on Si/SiGe measured by internal photoemission

Lowered‐barrier‐height silicide Schottky diodes are desirable for obtaining longer cutoff‐wave‐ length Si‐based infrared detectors. Silicide Schottky diodes have been fabricated by the reaction of evaporated Pt and Ir films on p‐Si1−xGex alloys with a thin Si capping layer. The onset of metal‐SiGe reactions was controlled by the deposited metal thickness. Internal photoemission measurements were made and the barrier heights were obtained from these. Pt‐SiGe and Ir‐SiGe reacted diodes have barrier heights of ∼0.27 and ∼0.31 eV, respectively, higher than typical values of 0.22 and 0.12 eV for the corresponding silicide/p‐Si diodes. Their emission constants are also lower and more voltage dependent than silicide/Si diodes. PtSi/Si/SiGe diodes, on the other hand, have lower barrier heights (∼0.15 eV) than the PtSi/Si barrier height. The barrier height shifts in such silicide/Si/SiGe diodes are interpreted by accounting for tunneling through the unconsumed Si layer. This is done analytically using a simple mod...

The PAU camera and the PAU survey at the William Herschel Telescope

The Physics of the Accelerating Universe (PAU) is a project whose main goal is the study of dark energy. For this purpose, a new large field of view camera (the PAU Camera, PAUCam) is being built. PAUCam is designed to carry out a wide area imaging survey with narrow and broad band filters spanning the optical wavelength range. The PAU Camera is now at an advance stage of construction. PAUCam will be mounted at the prime focus of the William Herschel Telescope. With the current WHT corrector, it will cover a 1 degree diameter field of view. PAUCam mounts eighteen 2k×4k Hamamatsu fully depleted CCDs, with high quantum efficiency up to 1 μm. Filter trays are placed in front of the CCDs with a technologically challenging system of moving filter trays inside the cryostat. The PAU Camera will use a new set of 42 narrow band filters ranging from ~4400 to ~8600 angstroms complemented with six standard broad-band filters, ugrizY. With PAUCam at the WHT we will carry out a cosmological imaging survey in both narrow and broad band filters that will perform as a low resolution spectroscopic survey. With the current survey strategy, we will obtain accurate photometric redshifts for galaxies down to iAB~22.5 detecting also galaxies down to iAB~24 with less precision in redshift. With this data set we will obtain competitive constraints in cosmological parameters using both weak lensing and galaxy clustering as main observational probes.

ProtoDESI: First On-Sky Technology Demonstration for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the universe using the baryon acoustic oscillations technique. The spectra of 35 million galaxies and quasars over 14,000 square degrees will be measured during a 5-year survey. A new prime focus corrector for the Mayall telescope at Kitt Peak National Observatory will deliver light to 5,000 individually targeted fiber-fed robotic positioners. The fibers in turn feed ten broadband multi-object spectrographs. We describe the ProtoDESI experiment, that was installed and commissioned on the 4-m Mayall telescope from August 14 to September 30, 2016. ProtoDESI was an on-sky technology demonstration with the goal to reduce technical risks associated with aligning optical fibers with targets using robotic fiber positioners and maintaining the stability required to operate DESI. The ProtoDESI prime focus instrument, consisting of three fiber positioners, illuminated fiducials, and a guide camera, was installed behind the existing Mosaic corrector on the Mayall telescope. A Fiber View Camera was mounted in the Cassegrain cage of the telescope and provided feedback metrology for positioning the fibers. ProtoDESI also provided a platform for early integration of hardware with the DESI Instrument Control System that controls the subsystems, provides communication with the Telescope Control System, and collects instrument telemetry data. Lacking a spectrograph, ProtoDESI monitored the output of the fibers using a Fiber Photometry Camera mounted on the prime focus instrument. ProtoDESI was successful in acquiring targets with the robotically positioned fibers and demonstrated that the DESI guiding requirements can be met.

Test benches facilities for PAUCam: CCDs and filters characterization

The PAUCam [1] is an optical camera with a 18 CCDs (Hamamatsu Photonics K.K.) mosaic and up to 42 narrow- and broad-band filters. It is foreseen to install it at the William Herschel Telescope (WHT) in the Observatorio del Roque de los Muchachos, Canary Islands, Spain. As required by the camera construction, a couple of test bench facilities were developed, one in Madrid (CIEMAT) that is mainly devoted to CCDs read-out electronics development and filter characterization [2], and another in Barcelona (IFAE-ICE) that has as its main task to characterize the scientific CCDs in terms of Dark Current, CTE, QE, RON and many other parameters demanded by the scientific performance required. The full CCDs characterization test bench layout, its descriptions and some optical and mechanical characterization results are summarized in this paper.

PAU camera: detectors characterization

The PAU Camera (PAUCam) [1,2] is a wide field camera that will be mounted at the corrected prime focus of the William Herschel Telescope (Observatorio del Roque de los Muchachos, Canary Islands, Spain) in the next months. The focal plane of PAUCam is composed by a mosaic of 18 CCD detectors of 2,048 x 4,176 pixels each one with a pixel size of 15 microns, manufactured by Hamamatsu Photonics K. K. This mosaic covers a field of view (FoV) of 60 arcmin (minutes of arc), 40 of them are unvignetted. The behaviour of these 18 devices, plus four spares, and their electronic response should be characterized and optimized for the use in PAUCam. This job is being carried out in the laboratories of the ICE/IFAE and the CIEMAT. The electronic optimization of the CCD detectors is being carried out by means of an OG (Output Gate) scan and maximizing it CTE (Charge Transfer Efficiency) while the read-out noise is minimized. The device characterization itself is obtained with different tests. The photon transfer curve (PTC) that allows to obtain the electronic gain, the linearity vs. light stimulus, the full-well capacity and the cosmetic defects. The read-out noise, the dark current, the stability vs. temperature and the light remanence.

Architecture of PAU survey camera readout electronics

PAUCam is a new camera for studying the physics of the accelerating universe. The camera will consist of eighteen 2Kx4K HPK CCDs: sixteen for science and two for guiding. The camera will be installed at the prime focus of the WHT (William Herschel Telescope). In this contribution, the architecture of the readout electronics system is presented. Back- End and Front-End electronics are described. Back-End consists of clock, bias and video processing boards, mounted on Monsoon crates. The Front-End is based on patch panel boards. These boards are plugged outside the camera feed-through panel for signal distribution. Inside the camera, individual preamplifier boards plus kapton cable completes the path to connect to each CCD. The overall signal distribution and grounding scheme is shown in this paper.

Silicide/SiGe Schottky diode infrared detectors

PtSi/Si/SiGe/Si Schottky diode IR detectors with extended and tunable cut-off wavelengths have been fabricated. Cut-off wavelengths depend on the SiGe composition and extend up to 10 micrometers for Si80Ge20. The cut-off wavelengths are also tunable by reverse bias. The tunability is due to the SiGe/Si offset serving as an additional potential barrier behind the Schottky barrier that can be varied in energy by a reverse bias. The sensitivity and range of the tunability is controlled by the SiGe thickness and composition. Cut-off wavelengths tunable from 4 micrometers at zero volts to 10 micrometers at 3 volts have been obtained. Quantum efficiency values are normal for operation at the long- wavelength end, but reduced over the rest of tunable range, because of the greater distance from the PtSi to the SiGe/Si offset.

Study of PtSi/Si(100) Interfaces by Ballistic -Electronemission Microscopy

The PtSi/Si interface is of technological interest for Schottky barrier infrared detectors. We are studying PtSi/Si heterostructures using ballistic -electron-emission microscopy (BEEM), an STM-based technique that uses the STM tip to inject hot electrons at a particular energy into the metal overlayer. The BEEM technique allows imaging of the Schottky barrier with good spatial resolution (of the order of tens of nanometers) and allows the measurement of the hot electron attenuation length in the metal overlayer. Our results indicate a Schottky barrier of 0.87 eV for PtSi/Si n-type, and an attenuation length of 4 nm for electrons with an energy of 1 eV above the metal Fermi level. The attenuation length we measure is a convolution of the electron elastic and inelastic mean free path lengths. We have also used an ac BEEM technique to observe inelastic scattering events at the metalsemiconductor interface in PtSi/Si(100) n-type. There are several features visible in the spectrum, including one at 1040 meV which we attribute to optical phonon-assisted electron-hole pair creation near the metal- semiconductor interface in analogy to a feature we have observed at the same energy in the Au/Si(100) ac BEEM spectrum. Higher-energy features appear at 1230 meV and 1300 meV. Similar features appeared in the Au/Si(100) spectrum at 1120 meV and 1230 meV. We also suggest that the traditional assumption of momentum conservation parallel to the Schottky barrier interface is unnecessary to obtain a quadratic turn on of the BEEM current above the threshold. If electrons are elastically scattered at the interface so that momentum is not conserved, the increase in the ratio of the density of states in the semiconductor to those in the metal will also give a quadratic turn on even when the band structure is much more complicated than a nearly free electron model. This model also explains why the simple square-root dependence of the photoresponse on wavelength above threshold observed in all metal/semiconductor Schottky barriers despite the complications in band structure.

The PAUCam readout electronics system

The PAUCam is an optical camera with a wide field of view of 1 deg x 1 deg and up to 46 narrow and broad band filters. The camera is already installed on the William Herschel Telescope (WHT) in the Canary Islands, Spain and successfully commissioned during the first period of 2015. The paper presents the main results from the readout electronics commissioning tests and include an overview of the whole readout electronics system, its configuration and current performance.

The PAU camera at the WHT

The PAU (Physics of the Accelerating Universe) project goal is the study of dark energy with a new photometric technique aiming at obtaining photo-z resolution for Luminous Red Galaxies (LRGs) roughly one order of magnitude better than current photometric surveys. To accomplish this, a new large field of view camera (PAUCam) has been built and commissioned at the William Herschel Telescope (WHT). With the current WHT corrector, the camera covers ~1 degree diameter Field of View (FoV). The focal plane consists of 18 2kx4k Hamamatsu fully depleted CCDs, with high quantum efficiency up to 1 μm. To maximize the detector coverage within the FoV, filters are placed in front of the CCDs inside the camera cryostat (made of carbon fiber material) using a challenging movable tray system. The camera uses a set of 40 narrow band filters ranging from ~4400 to ~8600 angstroms complemented with six standard broad-band filters, ugrizY. Here, we describe the camera and its first commissioning results. The PAU project aims to cover roughly 100 square degrees and to obtain accurate photometric redshifts for galaxies down to iAB ~ 22:5 detecting also galaxies down to iAB ~ 24 with less precision in redshift. With this data set we will obtain competitive constraints in cosmological parameters using both weak lensing and galaxy clustering as main observational probes.