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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).  

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).  

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Article
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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...

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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. ...
Context 2
... 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. ...
Context 3
... 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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... was obtained from the difference between the signals with and at 0 V bias voltage applied. Comparisons of the gain for different channel geometries (effect of channel length and aspect ratio) are plotted in Figure 14. ...

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Citations

... 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 . ...
Article
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 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. ...
Preprint
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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]. ...
Chapter
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. ...
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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. ...
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... 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. ...
Preprint
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.
... [26] Reports of a-Si:H based electronics on active matrix displays (AMLCD), and radiation detectors exist. [27,28] However, the quality of a-Si:H and dielectric-semiconductor interface determines the electrical performance and operational stability, which are compromised when using low-temperature fabrication processes. [29] Advantages of oxide-based semiconductors. ...
Thesis
Large-area electronics are considered to be a potential improvement to radiation detectors due to their low cost when compared to conventional systems. Currently, low-cost solutions cannot be achieved using traditional silicon technology. On the other hand, metal-oxide semiconductor-based thin-film transistors have shown great potential for large-area electronics. This potential is mostly due to the low processing temperature, and relatively simple fabrication methods when compared to Si-based technology. However, challenges in implementing oxide-based circuits still exist. For example, the deposition of the gate dielectric layers is at these low temperatures, which might result in a less than ideal gate dielectric with a higher oxide trap density; detrimental to the overall TFT performance and stability. Other aspects are the quality of the oxide semiconductor as well as the type of device to be fabricated (MOSFET, and MESFET). In this dissertation, the design and development of highly stable oxide-based field-effect transistors take place. The achieved performance and stability are by careful control of the metal-oxide-semiconductor deposition parameters. Moreover, several process integration strategies for ZnO-based preamplifiers and ultra-violet (UV) photodetectors appear. The radiation detectors show high sensitivity and relatively fast response to UV. A model to explain the increased stability of the resulting devices is also introduced.
... Thin-film materials such as hydrogenated amorphous silicon (˛-Si:H) have been widely used in semiconductor devices, energy applications, and MEMS sensors. Specifically, ˛-Si:H films are often used as structural thin films in optical pixel sensor [1], organic photodiodes for image sensing [2], active-matrix liquid crystal display (AMLCD) applications [3], structural color filters [4], particle detectors [5] and solar cells [6]. Also, amorphous silicon is commonly used as the sacrificial layers in the surface micromachining of MEMS devices [7]. ...
... Second, a-Si:H can be used for different types of detectors ranging from medical applications to particle physics and others; an overview is given in [318]. Such applications have in common that they profit from the large ratio of photoconductivity to dark conductivity, which manifests in a wide range of linear response. ...
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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.