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Hydrogenated Amorphous Silicon (a-Si:H) is a material well known for its intrinsic radiation hardness and is primarily utilized in solar cells as well as for particle detection and dosimetry. Planar p-i-n diode detectors are fabricated entirely by means of intrinsic and doped PECVD of a mixture of Silane (SiH4) and molecular Hydrogen. In order to develop 3D detector geometries using a-Si:H, two options for the junction fabrication have been considered: ion implantation and charge selective contacts through atomic layer deposition. In order to test the functionality of the charge selective contact electrodes, planar detectors have been fabricated utilizing this technique. In this paper, we provide a general overview of the 3D fabrication project followed by the results of leakage current measurements and x-ray dosimetric tests performed on planar diodes containing charge selective contacts to investigate the feasibility of the charge selective contact methodology for integration with the proposed 3D detector architectures., Submitted to JINST

Hydrogenated amorphous silicon (a-Si:H) can be produced by plasma-enhanced chemical vapor deposition (PECVD) of SiH4 (silane) mixed with hydrogen. The resulting material shows outstanding radiation hardness properties and can be deposited on a wide variety of substrates. Devices employing a-Si:H technologies have been used to detect many different kinds of radiation, namely, minimum ionizing particles (MIPs), X-rays, neutrons, and ions, as well as low-energy protons and alphas. However, the detection of MIPs using planar a-Si:H diodes has proven difficult due to their unsatisfactory S/N ratio arising from a combination of high leakage current, high capacitance, and limited charge collection efficiency (50% at best for a 30 µm planar diode). To overcome these limitations, the 3D-SiAm collaboration proposes employing a 3D detector geometry. The use of vertical electrodes allows for a small collection distance to be maintained while preserving a large detector thickness for charge generation. The depletion voltage in this configuration can be kept below 400 V with a consequent reduction in the leakage current. In this paper, following a detailed description of the fabrication process, the results of the tests performed on the planar p-i-n structures made with ion implantation of the dopants and with carrier selective contacts are illustrated.

Hydrogenated amorphous silicon (a-Si:H) has remarkable radiation resistance properties and can be deposited on a lot of different substrates. A-Si:H based particle detectors have been built since mid 1980s as planar p-i-n or Schottky diode structures; the thickness of these detectors ranged from 1 to 50 micron. However MIP detection using planar structures has always been problematic due to the poor S/N ratio related to the high leakage current at high depletion voltage and the low charge collection efficiency. The usage of 3D detector architecture can be beneficial for the possibility to reduce inter-electrode distance and increase the thickness of the detector for larger charge generation compared to planar structures. Such a detector can be used for future hadron colliders for its radiation resistance and also for X-ray imaging. Furthermore the possibility of a-Si:H deposition on flexible materials (like kapton) can be exploited to build flexible and thin beam flux measurement detectors and x-ray dosimeters., 10 pages 5 figures, 1 table

The vertex detectors for the future hadronic colliders will operate under proton fluencies above 1016 p/cm2. Crystalline Silicon detector technology, up to now, has kept the pace of the increasing fluencies in the LHC era and it is still the prevalent vertex detector material for the present and for the immediate future. Looking ahead in time, an alternative solution for such a detector has to be found because for the future there is no guarantee that Crystalline Silicon will hold this challenge. For this reason the development of hydrogenated amorphous silicon vertex detectors based on 3D-technology have been proposed and the technological solutions in order to build these detectors are described in this paper.

Hydrogenated amorphous silicon betavoltaic devices are studied both by simulation and experimentally. Devices exhibiting a power density of 0.1 μW/cm2 upon Tritium exposure were fabricated. However, a significant degradation of the performance is taking place, especially during the first hours of the exposure. The degradation behavior differs from sample to sample as well as from published results in the literature. Comparisons with degradation from beta particles suggest an effect of tritium rather than a creation of defects by beta particles.

Microchannel plates (MCP) based on hydrogenated amorphous silicon (a-Si:H) were recently introduced to overcome some of the limitations of crystalline silicon and glass MCP. The typical thickness of a-Si:H based MCPs (AMCP) ranges between 80 and 100 μm and the micromachining of the channels is realized by deep reactive ion etching (DRIE). Advantages and issues regarding the fabrication process are presented and discussed. Electron amplification is demonstrated and analyzed using Electron Beam Induced Current (EBIC) technique. The gain increases as a function of the bias voltage, limited to -340 V on account of high leakage currents across the structure. EBIC maps on 10° tilted samples confirm that the device active area extend to the entire channel opening. AMCP characterization with the electron beam shows gain saturation and signal quenching which depends on the effectiveness of the charge replenishment in the channel walls. © 2011 Elsevier B.V. All rights reserved.

The electron beam induced current (EBIC) technique was used to characterize a 32 lm thick hydrogenated amorphous silicon n–i–pdiode deposited on top of an ASIC, containing several channels of active feedback pre-amplifiers (AFP) with peaking time of 5 ns. Thehomogeneity of the sample together with the edge effects induced by the unevenness of the ASIC substrate were studied with low doses of10–30 keV electron beam. The degradation of a-Si:H pixel detectors was measured with intense electron beam. Their charge collectionand transient time were characterized with a 660 nm pulsed laser before and after the thermal annealing. All the diodes show approx-imately a full recovery of charge collection after thermal annealing. 2006 Elsevier B.V. All rights reserved. PACS: 73.61.Jc; 61.43.Dq; 29.40.Wk; 61.82.FkKeywords: Amorphous semiconductors; Detectors; Radiation; SEM; EBIC; ASIC 1. IntroductionElectron beam induced current (EBIC) is a powerfulsemiconductor analysis technique [1,2], which employs a10–30 keV electron beam from a scanning electron micro-scope (SEM) to scan the detector active area, and inducinga signal on the pixels’ electrodes. This signal can be directlyreadout or can be feedback to the SEM system in such away that any change in the generation, drift or recombina-tion of the generated carriers in the detector is displayed asvariations of contrast in EBIC images. EBIC imaging isvery sensitive to electron–hole recombination, so the EBICanalysis is very useful in finding defects such as voids,crystallographic imperfections, dislocations and grainboundaries.The EBIC method has a high potential for the character-ization of n–i–p hydrogenated amorphous silicon (a-Si:H)diodes on application specified integrated circuit (ASIC)[3], as it can also be used to study the electric field in thedepletion region and the degradation of a-Si:H with highdoses of electrons [4]. The EBIC signal depends primarilyon the strength of the electric field, so for a given potentialacross a junction, high dopant conditions result in narrowdepletion region and higher electric field, which can be usedto study the doping homogeneity. It must be noted that inaddition to electric field strength, the relative dimension ofdepletion region compared to generation volume is also animportant factor in EBIC collection efficiency. This is thereason why it is valuable to understand the basic devicestructure in order to interpret the results correctly.In this work, we tried to study the homogeneity of theactive area and the effects of the unevenness of the ASICsubstrate, which may induce regions with high electric field.This can also explain the high leakage currents that we

Thanks to their unique morphology, nanowires have enabled integration of materials in a way that was not possible before with thin film technology. In turn, this opens new avenues for applications in the areas of energy harvesting, electronics, and optoelectronics. This is particularly true for axial heterostructures, while core-shell systems are limited by the appearance of strain-induced dislocations. Even more challenging is the detection and understanding of these defects. We combine geometrical phase analysis with finite element strain simulations to quantify and determine the origin of the lattice distortion in core-shell nanowire structures. Such combination provides a powerful insight in the origin and characteristics of edge dislocations in such systems and quantifies their impact with the strain field map. We apply the method to heterostructures presenting single and mixed crystalline phase. Mixing crystalline phases along a nanowire turns out to be beneficial for reducing strain in mismatched core-shell structures.

Detection of scintillation light from LSO (Lutetiumoxyorthosilicate) crystals used in positron emission tomography (PET) is traditionally based on photo- multipliers. The proposal is to develop a novel photo- sensor, which is based on vertically integrating an hydrogenated amorphous silicon (a-Si:H) film on a pixel readout chip. The a-Si:H film is deposited with a n-i-p diode structure. The ASIC (Application Specific Integrated Circuit) performs both signal amplification and readout processing. The advantage of such an approach is the extremely compact and low-cost design, together with ultra- low noise signal retrieval. In addition the a-Si:H offers the technological advantage of direct deposition on the wafer thanks to the low deposition temperature. The article presents the results of quantum efficiency measured on different types of a-Si:H photodiodes deposited on glass (DC measurement) and CMOS circuit (AC measurement). Quantum Efficiency (QE) up to 80% has been measured at the wavelength of interest for the optimized photodiodes. © 2007 Elsevier B.V. All rights reserved.

Hybrid structures are formed from materials of different families. Traditionally, group IV and III–V semiconductors have not been integrated together in the same device or application. In this work we present a new approach for obtaining Si–GaAs hybrid heterostructures in nanowires based on a combination of molecular beam epitaxy and plasma enhanced chemical vapor deposition. Crystalline Si segments are integrated into GaAs nanowires grown by the Ga-assisted growth method at temperatures as low as 250 °C. We find that one of the most important factors leading to the successful growth of Si segments on GaAs is the silane–hydrogen dilution, which affects the concentration of silicon and hydrogen-based radicals (SiHx with x < 3) in the plasma, and determines if the Si shell is amorphous, polycrystalline or crystalline, and also if the growth takes place in the axial and/or radial directions. This work opens the path for the successful integration of silicon and III–V materials in one single nanowire.

Radiation hard monolithic particle sensors can be fabricated by a vertical integration of amorphous silicon particle sensors on top of CMOS readout chip. Two types of such particle sensors are presented here using either thick diodes or microchannel plates. The first type based on amorphous silicon diodes exhibits high spatial resolution due to the short lateral carrier collection. Combination of an amorphous silicon thick diode with microstrip detector geometries permits to achieve micrometer spatial resolution beneficial for high accuracy beam positioning. Microchannel plates based on amorphous silicon were successfully fabricated and multiplication of electrons was observed. This material may solve some of the problems related to conventional microchannel devices. Issues, potential and limits of these detectors are presented and discussed.

Pixel microvertex detectors at the SLHC and a future linear collider face very challenging issues: extreme radiation hardness, cooling design, interconnections density and fabrication cost. As an alternative approach we present a novel pixel detector based on the deposition of a Hydrogenated Amorphous Silicon (a-Si:H) film on top of a readout ASIC. The Thin-Film on ASIC (TFA) technology is inspired by an emerging microelectronic technology envisaged for visible light Active Pixel Sensor (APS) devices. We present results obtained with a-Si:H sensor films deposited on a glass substrate and on ASIC, including the radiation hardness of this material up to a fluence of 3.5×1015 p/cm2. © 2005 Elsevier B.V. All rights reserved.

About one third of all orchid species are deceptive, i.e., not providing any reward to their pollinator. Such species often have lower visitation rates compared to rewarding relatives. This could result in lower levels of geitonogamous selfing and thus would provide an advantage in term of progeny fitness through inbreeding avoidance. This hypothesis could be tested by comparing the level of inbreeding depression between deceptive and rewarding orchids. However, due to the difficulty to raise orchids from seeds, few studies of inbreeding depression are available, and most are focused on very early life stages, such as seed mass or embryo viability. Here, we present the results from an experimental investigation of inbreeding depression in the deceptive flower-colour dimorphic Dactylorhiza sambucina, from in vitro cultivation to greenhouse soil transplantation. We found strong inbreeding depression at all recorded stages (i.e., germination and survival), with estimates ranging from 0.47 to 0.75. Our study finally proposes a simple and suitable experimental protocol to raise orchids from seeds with high germination rates.

Image and particle sensors based on thin-film on CMOS technology are currently being developed at our laboratory. In this technology, amorphous silicon detectors are vertically integrated on top of dedicated CMOS chips. For both, vision and particle detection, this approach is expected to enhance the performances. In fact very high fill factors, increased sensitivity, and integration level, coupled with extremely low dark current density values can potentially be attained.A first optimization of the a-Si:H diodes (>1mm2) on glass substrates, with the primary focus on reducing dark current densities, gave Jdark values as low as 1 pA/cm2 (at -1 V for 1 m thick detectors). These detectors were then deposited on CMOS readout chips, but so far this step was unfortunately accompanied by an increase in Jdark to values over 10 nA/cm2.Here, the possible cause for such an increase in Jdark as well as possible “remedies” against this effect will be discussed; the principle cause is supposed to be the influence of chip topology. Possible solutions include surface treatments as well as the use of metal-i-p diode configuration. Results obtained so far with these methods are given.

Integrated imaging and particle sensors have been developed using thin-film on ASIC technology. For this purpose, hydrogenated amorphous silicon diodes, in various configurations, have been optimized for imaging and direct particle detection. These devices were first deposited on glass substrates and later on CMOS readout chips. With an optimization of the material properties and of the diode, a dark current of 1 pA/cm2 could be achieved on p-i-n structures at reverse bias voltage of 1 V. CMOS imagers, incorporating these optimized diodes were then fabricated and characterized. Very thick diodes (with thicknesses up to 50 μm) were also optimized and deposited on glass and on CMOS readout chips. Particle detectors in TFA technology with 12 and 30 μm a-Si:H n-i-p diodes have been fabricated and characterized using light pulse illumination. Direct detection of single low-energy beta particles has been demonstrated.

Vertically integrated particle sensors have been developed using thin-film on ASIC technology. Hydrogenated amorphous silicon n-i-p diodes have been optimized for particle detection. These devices were first deposited on glass substrates to optimize the material properties and the dark current of very thick diodes (with thickness up to 50 m). Corresponding diodes were later directly deposited on two types of CMOS readout chips. These vertically integrated particle sensors were tested in beta particle beam from 63Ni and 90Sr sources. Detection of single low- and high- energy beta particle was achieved.

Image and particle sensors based on thin film on CMOS (TFC) technology, where a-Si:H detectors are vertically integrated on top of a CMOS chip, basically provide high sensitivity and low dark current densities (Jdark). However, as shown in previous work and as confirmed by the actual measurements, Jdark values depend on the topology of the chip and on the detector structure used.The present paper describes a systematic study carried out, both with test structures on glass and also with a dedicated CMOS test chip designed by CERN. The increase in Jdark is shown to be related to border effects, and especially on the detailed structure of the pixel periphery. In all cases, lower Jdark are obtained when one uses metal-i-p instead of n-i-p configuration detectors. Transferring these results to the standard TFC sensors used by them, the authors have obtained values of Jdark as low as 20 pA/cm2 at -1 V reverse bias.

A new type of micro-channel plate detector based on hydrogenated amorphous silicon is proposed which overcomes the fabrication and performance issues of glass or bulk silicon ones. This new type of detectors consists in 80-100 μm thick layers of amorphous silicon which are micro-machined by deep reactive ion etching to form the channels. This paper focuses on the structure and fabrication process and presents first results obtained with test devices on electron detection which demonstrate amplification effects. Fabrication and performance issues are also discussed.

Radiation tests of 32 lm thick hydrogenated amorphous silicon n–i–p diodes have been performed using a high-energy 24 GeV pro-ton beam up to fluences of 2 · 10 16 protons/cm 2 . The results are compared to irradiation of similar 1 lm and 32 lm thick n–i–p diodesusing a proton beam of 405 keV at a fluence of 3 · 10 13 protons/cm 2 . All samples exhibited a drop of the photoconductivity and anincrease in the dark leakage current under both high- and low-energy proton irradiation. An almost full recovery of the device perfor-mance was observed after a subsequent thermal annealing. 2006 Elsevier B.V. All rights reserved. PACS: 29.40.Wk; 61.82.Fk; 73.61.JcKeywords: Silicon; Sensors 1. IntroductionVertical integration of hydrogenated amorphous silicon(a-Si:H) diodes on top of application-specific integratedcircuits (ASICs) is an interesting option for the next gener-ation of pixelized detectors for high-energy physics experi-ments. These innovative sensors offer advantages in termsof radiation hardness, interconnection density, integrationand cost. Recently, the authors have successfully developedsuch sensors, aiming at the detection of single charged par-ticles (b particles and protons) at the minimum ionizingenergy [1,2].Even though a-Si:H has been proven to have an excel-lent radiation hardness, most experiments have so far beenperformed in the context of testing the hardness of solarcells for space applications. In thin devices, the effects ofproton [3–5], neutron [6] and photon irradiation have allvery similar consequences on material and diode proper-ties: metastable deep defects are created than can beannealed out. The process has been very extensively studiedfor light-soaking but only few experiments have been car-ried out in the case of irradiation.In the present work, we first tried to investigate thelimits of thick a-Si:H diodes under high-energy protonbeams at the fluences that are expected for detectors infuture generations of particle colliders. Similar thickdiodes as well as thin ones were also degraded usinglow-energy proton beams and lower fluences as a meansof comparison with earlier irradiation experiments pub-lished in literature [3].2. ExperimentalThe 1.1 and 32.6 lm thick diodes were deposited by veryhigh-frequency plasma-enhanced chemical vapor deposi-tion at 70 MHz and 200 C at a deposition rate of15.6 A˚/s. Test devices (in the substrate–n–i–p configura-tion) were evaporated on Cr-coated glass and the pixel area(2 · 2or5· 5mm

Radiation tests of 32 μm thick hydrogenated amorphous silicon n-i-p diodes have been performed using a high energy 24 GeV proton beam up to fluences in excess of 1016 protons/cm2. The results are compared to irradiation of similar 1 μm and 32 μm thick n-i-p diodes using a proton beam of 280 keV at a fluence of 3x1013 protons/cm2. Even though both types of irradiation cause a significant drop in photoconductivity of thin or thick diodes, all samples survived the experiment and recover almost fully after a subsequent thermal annealing.

Image sensors based on thin-film on CMOS technology (TFC) have been developed. In this approach, amorphous silicon (a-Si:H) detectors are vertically integrated on top of a CMOS readout chip so as to form monolithic image sensors. In order to reduce as far as possible the dark current density (Jdark) of the TFC sensors, we have focused on analyzing and understanding the behavior of Jdark in this type of detectors. Edge effects along the periphery and at the corners of the pixel, due to the non planar configuration of the vertically integrated photodiodes, are found to be responsible for an increase of the dark current. A new and adapted solution for the minimization of Jdark is proposed, which combines the use of a metal-i-p a-Si:H diode configuration with a deposition on top of an unpassivated CMOS chip. Values of Jdark as low as 12 pA/cm2 at a reverse polarization of V = -1 V are measured on such TFC sensors.