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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).
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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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Citations
... After the first successful doping attempt, it was possible to use this material in electronics, solar cells, and radiation detectors [2][3][4]. The most used deposition technique for this material is plasma-enhanced chemical vapor deposition (PECVD) from a mixture of silane (SiH 4 ) and hydrogen at temperatures of about 180-250 • C [5]. The low deposition temperature of a-Si:H allows its layering on flexible materials like polyimide (PI). ...
Hydrogenated amorphous silicon (a-Si:H) devices on flexible substrates are currently being studied for application in dosimetry and beam flux measurements. The necessity of in vivo dosimetry requires thin devices with maximal transparency and flexibility. For this reason, a thin (<10 µm) a-Si:H device deposited on a thin polyimide sheet is a very valid option for this application. Furthermore, a-Si:H is a material that has an intrinsically high radiation hardness. In order to develop these devices, the HASPIDE (Hydrogenated Amorphous Silicon Pixel Detectors) collaboration has implemented two different device configurations: n-i-p type diodes and charge-selective contact devices.Charge-selective contact-based devices have been studied for solar cell applications and, recently, the above-mentioned collaboration has tested these devices for X-ray dose measurements. In this paper, the HASPIDE collaboration has studied the X-ray and proton response of charge-selective contact devices deposited on Polyimide. The linearity of the photocurrent response to X-ray versus dose-rate has been assessed at various bias voltages. The sensitivity to protons has also been studied at various bias voltages and the wide range linearity has been tested for fluxes in the range from 8.3 × 107 to 2.49 × 1010 p/(cm2 s).
... Hydrogenated amorphous silicon (a-Si:H) is known for being one of the most radiation-resistant semiconductors and, for this reason, it has been studied in the eighties and nineties as an active material for particle detection in high-energy physics experiments, but without much practical use (Wyrsch and Ballif, 2016). The amorphous nature of a-Si:H with a high content of hydrogen, which passivates intrinsic defects renders this material quite immune to radiation defects. ...
... However, this device with selective contacts remains still mostly undepleted as a bias voltage greater than 200 V is probably needed to achieve full depletion. It should be noted that the voltage needed for full depletion scales as the square of the thickness (Wyrsch and Ballif, 2016). All measurements are summarised in Table 1 (note that not all of them are plotted in figures). ...
... The material a-Si:H is known to be metastable (Wyrsch and Ballif, 2016;Street, 1991). Defects are created by recombination events, which may take place as soon as electron-hole pairs are created independently of the pair creation origin (light or particles) (Street, 1991;Frietzsche, 2001). ...
Ultra-high dose rate radiation therapy (FLASH) based on proton irradiation is of major interest for cancer treatments but creates new challenges for dose monitoring. Amorphous hydrogenated silicon is known to be one of the most radiation-hard semiconductors. In this study, detectors based on this material are investigated at proton dose rates similar to or exceeding those required for FLASH therapy. Tested detectors comprise two different types of contacts, two different thicknesses deposited either on glass or on polyimide substrates. All detectors exhibit excellent linear behaviour as a function of dose rate up to a value of 20 kGy/s. Linearity is achieved independently of the depletion condition of the device and remarkably in passive (unbiased) conditions. The degradation of the performance as a function of the dose rate and its recovery are also discussed.
... The minimum amount of H necessary to passivate most of the dangling bonds is about 1% atomic. The increase of H content enlarges the bandgap hence reducing the background current of the device, and ∼ 14% is the typical value to obtain a detector grade device Wyrsch and Ballif (2016). The bandgap depends also on the deposition conditions such as the temperature. ...
The characteristics of a hydrogenated amorphous silicon (a-Si:H) detector are presented here for monitoring in space solar flares and the evolution of strong to extreme energetic proton events. The importance and the feasibility to extend the proton measurements up to hundreds of MeV is evaluated. The a-Si:H presents an excellent radiation hardness and finds application in harsh radiation environments for medical purposes, for particle beam characterization and, as we propose here, for space weather science applications. The critical flux detection limits for X rays, electrons and protons are discussed.
... 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.
