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Schematic particle detection schemes of x-rays: direct detection using a thick diode (left) and indirect detection using a thin diode and a scintillating layer (right).
Source publication
Hydrogenated amorphous silicon (a-Si:H) is attractive for radiation detectors because of its
radiation resistance and processability over large areas with mature Si microfabrication
techniques. While the use of a-Si:H for medical imaging has been very successful, the
development of detectors for particle tracking and minimum-ionizing-particle detec...
Contexts in source publication
Context 1
... this case, a much thinner photodiode can be used. A schematic drawing of the two detection schemes is given in Figure 1. An n-i-p (n-doped, intrinsic and p-doped layers) diode structure is used to collect e-h pairs created either by the ionizing particle (charged particles or photons), depending on the detection scheme. ...
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... high spatial resolution can therefore be achieved using pixelated devices or micro-strips [81]. Figure 10 shows an EBIC image of a set of micro-strips connected in parallel covered with a 5-µm-thick a-Si:H n-i-p diode. Each micro-strip (1.5 µm wide and spaced by 3.5 µm) is clearly resolved. ...
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... most have their peak emission at UV or deep blue wavelengths, which are more difficult to record using a-Si:H photodiodes [89]. However, a-Si:H n-i-p photodiodes with thinner p-doped layers and an optimized front transparent electrode (transparent conductive oxide, TCO), or photodiodes in the reverse configuration (p-layer at the back with respect to illumination) without an n-layer, can achieve high external quantum efficiency at wavelengths of interest, as shown in Figure 11. While an integrated device combining a fast scintillator, a-Si:H diodes and readout electronics has not yet been tested, the performance of the individual components seems sufficient to allow for gamma detection in PET scanners [89]. ...
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... a high electric field is applied between the two faces of the plate, the primary electrons multiply by impact ionization forming an avalanche within the microchannels. A schematic view of such a device and its functioning is shown in Figure 12. Gains in excess of 1000 can be achieved from a single plate. ...
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... new generation was designed featuring an additional electrode at the back, separated from the bottom readout electrode (anodes) by a thin insulating layer [101]. The overall device structure and detailed scanning electron microscope (SEM) images of the device are given in Figure 13. In this configuration, the bias electric field used to induce avalanches and electron multiplication is applied between the top and intermediate electrode, while the bottom electrode is used for readout and is therefore insulated from the leakage current. ...
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Citations
... This demonstrates the reversible nature of radiation damage on a-Si:H detectors, and its potential for beam monitoring and tracking. For a given thickness (thin) of material, a-Si:H does show superior radiation hardness compared to materials such as crystalline Si, InP/GaAs/Ge, CIGS, and CdTe [41]. Lower energy protons (405 keV) have a higher possibility of being stopped by the material, and the hydrogen atom becomes embedded inside the detector. ...
Silicon tracking detectors have grown to cover larger surface areas up to hundreds of square meters, and are even taking over other sub-detectors, such as calorimeters. However, further improvements in tracking detector performance are more likely to arise from the ability to make a low mass detector comprised of a high ratio of active sensor to inactive materials, where dead materials include electrical services, cooling, mechanical supports, etc. In addition, the cost and time to build these detectors is currently large. Therefore, advancements in the fundamental technology of tracking detectors may need to look at a more transformative approach that enables extremely large area coverage with minimal dead material and is easier and faster to build. The advancement of thin film fabrication techniques has the potential to revolutionize the next-to-next generation of particle detector experiments. Some thin film deposition techniques have already been developed and widely used in the industry to make LED screens for TVs and monitors. If large area thin film detectors on the order of several square meters can be fabricated with similar performance as current silicon technologies, they could be used in future particle physics experiments. This paper aims to review the key fundamental performance criteria of existing silicon detectors and past research to use thin films and other semi-conductor materials as particle detectors in order to explore the important considerations and challenges to pursue thin film detectors.
... Hydrogenated amorphous silicon thin films (a-Si:H) 35 with different compositions, structures, and dopants may present a broad range of properties depending on the goal. They are, therefore, potential candidates for use in a diverse set of fields, 35 including photovoltaic studies, 36−38 particle detectors, 39 and thin-film transistors (TFTs). 40 Recently, 41 this material was also reported as a stable, potential solid lubricant at the macroscale and under high temperatures (up to 600°C), with results close to superlubricity. ...
Silicon-based materials are widely applied in micro- and nanoscale
devices, such as micro- and nano-electromechanical systems (MEMs and NEMs,
respectively). However, the nanofriction behavior of such materials is still an issue
that influences or hinders some applications. Recently, a sliding-dependent friction
mechanism was accessed, by simulation of hydrogenated silicon surfaces, in which
friction forces increase during sliding. The experimental evaluation of this
phenomenon is still lacking, as well as the confirmation of such a behavior in
ambient air conditions, related to the current application. Here, the nanotribology
of hydrogenated amorphous silicon (a-Si:H) was experimentally studied under
repeated scanning. As an overall analysis, friction increases during sliding, without
wear. After separation and new contact, the friction force recovers an intermediate value and increases again, until reaching an
intermediate steady state. The mechanism may be related to the successive creation and breaking of bonds at the interface. When the
contact is ceased, the dangling bonds created at both surfaces after separation may be repassivated. Moreover, the relationship of this
behavior with the photoactivity of the material was tested. If an external light source is added during the scanning, it only changes the
results before the stabilization of the interface. This detailed experimental study might promote the broader nanoapplication of the
material, addressing the current failures and suggesting new devices based on the anomalous behavior.
... The hydrogenation saturates most of the dangling bonds, lowering the density of the defects to 10 15 cm −3 . The typical amount of hydrogen required to obtain a-Si:H quality for detector applications is in the order of 10% atomic hydrogen [4] The inclusion of hydrogen has the additional effect of increasing the band gap to 1.7-1.9 eV [5]. ...
In this paper, by means of high-resolution photoemission, soft X-ray absorption and atomic force microscopy, we investigate, for the first time, the mechanisms of damaging, induced by neutron source, and recovering (after annealing) of p-i-n detector devices based on hydrogenated amorphous silicon (a-Si:H). This investigation will be performed by mean of high-resolution photoemission, soft X-Ray absorption and atomic force microscopy. Due to dangling bonds, the amorphous silicon is a highly defective material. However, by hydrogenation it is possible to reduce the density of the defect by several orders of magnitude, using hydrogenation and this will allow its usage in radiation detector devices. The investigation of the damage induced by exposure to high energy irradiation and its microscopic origin is fundamental since the amount of defects determine the electronic properties of the a-Si:H. The comparison of the spectroscopic results on bare and irradiated samples shows an increased degree of disorder and a strong reduction of the Si-H bonds after irradiation. After annealing we observe a partial recovering of the Si-H bonds, reducing the disorder in the Si (possibly due to the lowering of the radiation-induced dangling bonds). Moreover, effects in the uppermost coating are also observed by spectroscopies.
... However, doping also introduces many additional defects, and for this reason direct p-n junction cannot be used as active material in particle detectors and solar cells. Therefore, the simplest detector structures that have been fabricated and successfully tested are p-i-n diodes or Schottky diodes [10]. ...
... Many different kinds of particles have been detected using planar diode devices, including MIPs [10], x-rays [15], neutrons using both boron [16] or gadolinium converters [17], alpha particles [18], and heavier ions [19]. ...
... The results of this test are shown in Figure 3 for a set of micro-strips (1.5 μm wide and spaced by 3.5 μm) on a 5 μm thick a-Si:H n-i-p diode. From this figure, it is evident that the signals from the strips are clearly separated because the lateral charge spread is in the order of few microns [10]. Cross talk (i.e., induced signal in neighbor strips) has been measured in another experiment with a beta source and was found to be negligible [22]. ...
Hydrogenated amorphous silicon (a-Si:H) particle detectors have been considered as alternatives to crystalline silicon detectors (c-Si) in high radiation environments, due to their excellent radiation hardness. However, although their capability for particle flux measurement in beam monitoring applications is quite satisfactory, their minimum ionizing particle (MIP) detection has always been problematic because of the poor signal-to-noise ratio caused by a low charge collection efficiency and relatively high (compared to crystalline silicon) leakage current. In this article, after a review of the status of technological research for a-Si:H detectors, a perspective view on MIP detection and beam flux measurements with these detectors will be given.
... From the data presented in figure 2 it is observed that AZO devices have a lower leakage current compared to the TiO 2 device, and that thinner devices at the same field have a lower current in comparison to their thicker counterparts in agreement with what reported in ref. [3] for doped contacts. The overall value of the leakage current normalized to the area for an 8.2 μm device with AZO selective contact at 5 V/μm bias is in the order of 9.2 nA/cm 2 for sample 1 and 14.8 nA/cm 2 for sample 2, while for the TiO 2 device is 24.4 nA/cm 2 . ...
Hydrogenated Amorphous Silicon (a-Si:H) is a well known material 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 (SiH 4 ) 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.
... Hydrogenated amorphous silicon (a-Si:H) is a disordered semiconductor obtained via plasma-enhanced chemical vapor deposition (PECVD) of a mixture of silane (SiH 4 ) and hydrogen at temperatures of 250-300 • C [1]. The resulting material has an irregular arrangement of atoms resulting in not all Si-Si bonds being saturated, leading to the presence of dangling bonds (DBs) that are related to the presence of intermediate states between the valence and the conduction bands. ...
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) is a disordered semiconductor obtained from PECVD (plasma-enhanced chemical vapour deposition) of a mixture of Silane (SiH4) and Hydrogen at temperatures of 250-300 °C [1]. The resulting material has an irregular arrangement of atoms where not all Si-Si bonds are actually saturated, leading to the presence of dangling bonds (DBs) that are related with the presence of intermediate states between the valence and the conduction bands. ...
Hydrogenated amorphous silicon (a-Si:H) can be produced by plasma-enhanced chemical vapour deposition (PECVD) of SiH4 (Silane) mixed with Hydrogen. The resulting material shows outstanding radiation resistance properties and can be deposited on a wide variety of different substrates. These devices have been used to detect many different kinds of radiation namely: MIPs, x-rays, neutrons and ions as well as low energy protons and alphas. However, MIP detection using planar diodes has always been difficult due to the unsatisfactory S/N ratio arising from a combination of high leakage current, high capacitance and a limited charge collection efficiency (50% at best for a 30 µm planar diode). To overcome these limitations the 3D-SiAm collaboration proposes to use a 3D detector geometry. The use of vertical electrodes allows for a small collection distance to be maintained while conserving a large detector thickness for charge generation. The depletion voltage in this configuration can be kept below 400 V with 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 will be illustrated.
... Besides applications for terrestrial large-scale energy production, amorphous siliconbased solar cells have also been proposed for space solar cells [1] or as an active material for radiation detectors [2,3]. Generally, it has been reported that amorphous silicon has a much better radiation tolerance to energetic ions than crystalline silicon [4]. ...
Amorphous silicon-based thin-film minimodules have been irradiated with 68 MeV protons up to a dose of 1 × 10¹² protons/cm². During the irradiation, the solar cell current under short circuit conditions, due to the photogeneration of charge carriers by the low-intensity room light and the radiation-induced generation of charge carriers, has been measured. Whereas the degradation of the photo-induced current can be continuously monitored during the experiment, the smaller radiation-induced current is only visible in current discontinuities at the beginning and the end of the radiation period. In our experiment, we measured a very similar decrease in the photo- and the radiation-induced current, both due to the proton irradiation. Therefore, we can infer that the degradation of the solar cells’ photoelectrical properties is mainly due to the degradation of the amorphous silicon active material and only to a smaller content to the glass substrate’s optical transmission properties. Directly after irradiation, we observed a continuous recovery of the photo-induced current, due to the room-temperature annealing of the electronic defects created in the amorphous silicon absorber layer.
... The desirability of a-Si:H is in part owed not only to the capability of the material to be deposited over a large area (i.e., without the need for physical tiling) but also to be deposited above a variety of different substrates including flexible materials like polyamide (kapton), opening up a myriad of potential applications in radiation detection physics [6]. Furthermore, it's becoming increasingly desirable in particle detector applications, given its low cost and superior radiation tolerance [7,8]. This radiation hardness can be accounted for in the disordered structure inherent to a-Si:H, and the passivation of delocalized states or defects through the introduction of high concentrations of hydrogen. ...
... The distribution of defects within the band structure of a-Si:H can be described by the defect pool model developed in 1990 in order to model solar cells [9]. DBs act as recombination centers or defects within the a-Si:H material and are present as a continuous distribution of states within E g [2,8]. These states can be classified as either extended "tails" of the valence and conduction bands, or as a localized distribution of states within E g . ...
... In this study, we chose to model a simplified 2D version of the n-i-p (n-doped, intrinsic, and p-doped layers) a-Si:H diode structure as described by Wyrsch et al. [8]. The geometry depicted in Figure 2, features a 90 nm thick n-type layer upon a 30 µm thick intrinsic layer upon a 90 nm thick p-type layer. ...
There is currently a renewed interest in hydrogenated amorphous silicon (a-Si:H) for use in particle detection applications. Whilst this material has been comprehensively investigated from a numerical perspective within the context of photovoltaic and imaging applications, the majority of work related to its application in particle detection has been limited to experimental studies. In this study, a material model to mimic the electrical and charge collection behavior of a-Si:H is developed using the SYNOPSYS©Technology Computer Aided Design (TCAD) simulation tool Sentaurus. The key focus of the model is concerned with the quasi-continuous defect distribution of acceptor and donor defects near the valence and conduction bands (tails states) and a Gaussian distribution of acceptor and donor defects within the mid-gap with the main parameters being the defect energy level, capture cross-section, and trap density. Currently, Sentaurus TCAD offers Poole-Frenkel mobility and trap models, however, these were deemed to be incompatible with thick a-Si:H substrates. With the addition of a fitting function, the model was able to provide acceptable agreement (within 10 nA cm−2) between simulated and experimental leakage current density for a-Si:H substrates with thicknesses of 12 and 30 μm. Additional transient simulations performed to mimic the response of the 12 μm thick device demonstrated excellent agreement (1%) with experimental data found in the literature in terms of the operating voltage required to deplete thick a-Si:H devices. The a-Si:H model developed in this work provides a method of optimizing a-Si:H based devices for particle detection applications.
... Best quality materials exhibit 4 to 10% atomic hydrogen content. More details on the deposition of a-Si:H for detector application can be found in ref. [7]. After a-Si:H deposition on the substrate, silicon nitride will be deposited on the a-Si:H layer for passivation using PECVD at low temperature (e.g. ...
... In order to tune some empirical parameters and to verify the correctness of our simulation we compare the results of our simulation program with the measurements taken from two devices having thickness of 12 and 30 µm. The simulated model features a simplified 2D version of the n-i-p (n-doped, intrinsic and p-doped layers) a-Si:H diode structure as described by Wyrsch et al. [7]. The simulated device, features a 90 nm thick n-type layer upon a 30 or 12 µm thick intrinsic layer upon a 90 nm thick p-type layer. ...
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 um. 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.
