SiC Radiation Research Articles

Performance of 4H–SiC radiation detector after high flux proton and Fe13+ heavy ion beam irradiation

A batch of Schottky diode 4H–SiC detectors was fabricated by using Ni/Au electrodes, which were irradiated by Fe13+ heavy ion beam current with a flux of 1 × 1013 n/cm2 to 4.35 × 1014 n/cm2 in a stepwise increment, the forward and reverse I–V characteristics before and after irradiation as well as the energy resolution of α particles produced by 241Am source were tested and compared. The test results show that the reverse leakage current of the 4H–SiC detector that we made after the radiation of Fe13+ heavy ion beam increases gradually with the increase of the irradiation flux, Schottky Barrier Height decreases continuously where the ideal factor gradually increases. When the flux is 4 × 1013 n/cm2, it has risen to 9 μA, but the detector still has an energy resolution of 2.63%. When the flux of Fe13+ heavy ion beam is increased to 8 × 1013 n/cm2, the very obvious degradation phenomenon appears, the Charge Collection Efficiency(CCE) is reduced from 100% to 66.08%, the energy resolution is changed from 1.6% to 4.33%. When flux is increased to 1.4 × 1014 n/cm2, and the detector's performance has degraded seriously, in which the energy resolution is decreased from 1.76% to 9.54%, meanwhile the CCE is reduced from 100% to 64.84%, but it can still be used. As the beam flux reaches 2 × 1014 n/cm2, the detector has been completely damaged. At the same time, the ability of the detector to be resist mixed ion beam irradiation was tested. The 4H–SiC detector still has an energy resolution of 2.51% after receiving a dose of irradiation, which concluded with 1 × 1017 n/cm2 protons and 2 × 1013 n/cm2 Fe13+ heavy ion beams.

Spectrometric performance of SiC radiation detectors at high temperature

In this work, we have investigated the performance of a 4H–SiC radiation sensor in the temperature range from 25 °C to 450 °C to explore its compatibility as detector of fast ion losses in plasma diagnostic of future nuclear fusion reactors. To simulate the escape of fusion-born alpha particles in D-T (deuterium-tritium) fusion plasmas, spectroscopic measurements were carried out in a vacuum chamber by irradiating the detector with a 3.5 MeV alpha beam from a Tandem accelerator. The detector was found to have an energy resolution ≤2% over the entire temperature range analyzed. Relevantly, the excellent spectrometric capabilities of the device have allowed us to calculate from experimental data, with unprecedented accuracy, the average energy required to create a single electron-hole pair in 4H–SiC as a function of temperature.

Investigation of Linear Current in SiC Radiation Detector

Investigation of Linear Current in SiC Radiation Detector

Monolithic Integration of Graphene in SiC Radiation Sensors for Harsh-Environment Applications

Due to their low leakage current, low noise levels, high thermal conductivity, and potential radiation hardness, SiC devices offer various advantages over Si devices in certain applications. As a result, they are being considered for operation in harsh environments, such as plasma diagnostic systems in future nuclear fusion reactors or in high energy physics applications. We report on relevant results of the GRACE project, which seeks to deliver a new generation of SiC sensors with graphene-enhanced contacts. Such devices are aimed to be radiation-hard and functional at high temperatures. The work presented in this paper focuses on the optimisation of the electrical contacts, along with the electrical characterisation and radiation-tolerance assessment of the first sensor prototypes produced.

Improved performance of SiC radiation detectors due to optimized ohmic contact electrode by graphene insertion

SiC as a typical wide bandgap semiconductor has exhibited potential application in alpha particle detectors. However, due to the comparatively high annealing temperature required for traditional fabrication technique of ohmic electrode, it is easy to excite impurities in the SiC epilayer, which act as scattering centers result in the declined device performance. In present work, a graphene layer is inserted between metal ohmic electrode and SiC. The graphene promotes the formation of carbon compounds and thus decreases ohmic contact resistance. Meanwhile, due to the Fermi level adjustable of graphene by external bias, the barrier of interface at graphene insert layer is enlarged at reverse bias. The built-in field accelerates the separation of photo-generated electron-hole pairs. As a result, the graphene inserted device annealed at 400 °C achieved a 3.9%@-40 V energy resolution, and the device even without annealing achieved a 4.4%@-40 V energy resolution for 239Pu alpha source, which are both better than that of traditional device without graphene layer annealed at 880 °C (6%@-40 V). The detailed mechanism has been discussed and suggested. Present work provides an effective strategy to improve device performance.

Improved performance of SiC radiation detector based on metal–insulator–semiconductor structures

SiC is a typical wide bandgap semiconductor that has demonstrated potential applications in radiation detection and imaging, but its performance must be improved from both a material quality and device design standpoint. In this study, based on a theoretical analysis, we found that it is possible to improve the performance of SiC radiation detectors by changing the device structure from a metal/semiconductor to a metal/insulator/semiconductor design and fabricate and evaluate corresponding devices with α particle radiation detection. We experimentally confirmed that introducing an SiO2 dielectric layer can effectively improve the energy resolution of detectors, so the effect of the dielectric layer thickness on detectors’ performance was further investigated and clarified. We demonstrated that a device with a 100 nm SiO2 dielectric layer on a 15μm SiC epitaxial layer achieved the best energy resolution of 0.55% @-40 V under 5.48 MeV alpha particle irradiation. This study provides further insight to accelerate commercial applications of SiC radiation detectors.

Simulation of SiC radiation detector degradation**Project supported by the National Key R&D Program of China (Grant No. 2016YFB0400400).

Simulation on the degradation of 4H-SiC Schottky detector was carried out using ISE TCAD, and the limit of the drift-diffusion analytical model was discussed. Two independent defect levels, rather than a pair of specific carrier lifetime, were induced to describe Z1/2 defects in simulation to calculate the charge collection efficiency versus bias voltage. Comparison between our calculation and the reported experimental results shows that an acceptable agreement was achieved, proving the feasibility of regarding Z1/2 defect as two individual defect levels. Such a treatment can simplify the simulation and may help to further investigate the detector degradation.

Detection of fast neutrons from D–T nuclear reaction using a 4H–SiC radiation detector

The particle detector based on a high purity epitaxial layer of 4H–SiC exhibits promising properties in detection of various types of ionizing radiation. Due to the wide band gap of 4H–SiC semiconductor material, the detector can reliably operate at room and also elevated temperatures. In this work we focused on detection of fast neutrons generated the by D–T (deuterium–tritium) nuclear reaction. The epitaxial layer with a thickness of 105 [Formula: see text]m was used as a detection part. A circular Schottky contact of a Au/Ni double layer was evaporated on both sides of the detector material. The detector structure was characterized by current-voltage and capacitance-voltage measurements, at first. The results show very low current density (<0.1 nA/cm[Formula: see text] at room temperature and good homogeneity of free carrier concentration in the investigated depth. The fabricated detectors were tested for detection of fast neutrons generated by the D–T reaction. The energies of detected fast neutrons varied from 16.0 MeV to 18.3 MeV according to the acceleration potential of deuterons, which increased from 600 kV up to 2 MV. Detection of fast neutrons in the SiC detector is caused by the elastic and inelastic scattering on the silicon or carbide component of the detector material. Another possibility that increases the detection efficiency is the use of a conversion layer. In our measurements, we glued a HDPE (high density polyethylene) conversion layer on the detector Schottky contact to transform fast neutrons to protons. Hydrogen atoms contained in the conversion layer have a high probability of interaction with neutrons through elastic scattering. Secondary generated protons flying to the detector can be easily detected. The detection properties of detectors with and without the HDPE conversion layer were compared.

Influence of the Annealing Process for the Metal Contacts of the SiC Semiconductor Radiation Detector

We have studied the radiation response of a prototype SiC radiation detector by using a 6H-SiC wafer. Metal contacts on the surface of the SiC samples were fabricated by using a thermal evaporator in a vacuum condition. Among the SiC samples, several samples were heated by a Rapid Temperature Annealing(RTA) device for 10 minutes at 300°C. The metal contacts on the annealed and non-annealed samples were scanned by using AFM(Atomic Force Microscope) before and after an annealing process. The current-voltage characteristics of the SiC detectors were measured by parameter analyzer and the radiation response was evaluated by 238Pu with 5.5 MeV α-ray at room temperature and a atmospheric pressure. After annealing process, the surface roughness and the current-voltage characteristics decreased. The Schottky barrier heights of non-annealed and annealed SiC samples were determined as 0.638 eV and 0.688 eV, respectively. Also radiation response spectra of the annealed and non-annealed detectors were similar.

Study of the current–voltage characteristics of a SiC radiation detector irradiated by Co-60 gamma-rays

The SiC semiconductor has recently emerged as an attractive material for an ionization radiation detection. A wide bandgap (3.03 eV) and high radiation damage resistance allow for the fabrication of detectors capable of operating at a high-temperature and in high radiation fields. The major aim of our study is to develop a robust detector which will be applied to harsh radiation environments. In this study, we fabricated the SiC radiation detectors and measured the current–voltage characteristics of SiC detectors irradiated by Co-60 gamma-ray source. The I– V curves showed a decrease of the leakage current with increasing dose rate of Co-60 gamma-ray in the 0–100 V bias voltage range.

Influence of irradiation by 24 GeV protons on the properties of 4H–SiC radiation detectors

We had investigated the effects of the irradiation by 24 GeV protons with the doses from 10 13 cm − 2 up to 10 16 cm − 2 on the properties of radiation detectors fabricated as Schottky diodes on 4H–SiC. Numbers and activities of radionuclides and isotopes produced after the irradiation were analysed. Activities of 7Be and 22Na were found to be proportional to the irradiation dose and ranged from 1.3 up to 890 Bq and from 1.9 up to 950 Bq, respectively. The total amount of formed stable isotopes was from 1.2 × 10 11 cm − 2 up to 5.9 × 10 13 cm − 2 . 390 days after the irradiation the number of radiated electrons with different energies ranged from 1.0 up to 600 per second, respectively. The contact properties were investigated by means of the current–voltage analysis. At lower irradiation doses a slight decrease of the effective potential barrier height from about 0.74 eV down to < 0.7 eV took place. The reverse current of the diodes grew by up to one order of magnitude. At the doses above 3 × 10 15 cm − 2 opposite changes were observed. Irradiation by up to 1 × 10 16 protons/cm − 2 , resulted in the increase of the potential barrier height up to ∼ 0.85 eV, followed by the drop of the reverse current by up to two orders of magnitude. The observed effects were explained by the appearance of the disordered material structure because of the high-energy particle bombardment.

Silicon Carbide for Alpha, Beta, Ion and Soft X-Ray High Performance Detectors

High performance SiC detectors for ionising radiation have been designed, manufactured and tested. Schottky junctions on low-doped epitaxial 4H-SiC with leakage current densities of few pA/cm2 at room temperature has been realised at this purpose. The epitaxial layer has been characterised at different dose of radiations in order to investigate the SiC radiation hardness. The response of the detectors to alpha and beta particle and to soft X-ray have been measured. High energy resolution and full charge collection efficiency have been successfully demonstrated.

Investigation of 4H-SiC Schottky diodes by ion and X-ray micro beam induced charge collection techniques

Silicon carbide has recently emerged as an attractive material for ionisation radiation detection. The high band gap and high radiation damage resistance should allow the fabrication of detectors capable to operate at high temperature and in high radiation fields. The development of SiC radiation detectors in the field of spectroscopy imposes severe constraints in the electronic quality and homogeneity of the material. In this work we present an investigation of the charge collection properties of ‘detector grade’ 4H-SiC Schottky diodes performed by means of the X-ray and ion beam induced charge collection (XBICC and IBIC) techniques. Such techniques allow the minority carrier diffusion length of the material to be evaluated and mapping of the transport properties to be performed with a spatial resolution of the order of 1 μm. The investigated detectors are formed by Schottky contact (Au) on the epitaxial layer and an ohmic contact on the back side of 4H-SiC substrates. IBIC measurements were performed using protons of energy 0.7–1.7 MeV. The IBIC spectra show a complete charge collection generated by ionisation in the depletion region. Similar analysis was also performed in steady state conditions using data from photocurrent measurements carried out at European Synchrotron Radiation Facility using 3 keV photons. IBIC and XBICC maps were obtained by recording the mean pulse height and the mean photocurrent as a function of the photon or ion impact co-ordinates. The analysis of such maps allowed us to individuate the spatial distribution of defects and contact imperfections.

Performance of bulk SiC radiation detectors

SiC is a wide-gap material with excellent electrical and physical properties that may make it an important material for some future electronic devices. The most important possible applications of SiC are in hostile environments, such as in car/jet engines, within nuclear reactors, or in outer space. Another area where the material properties, most notably radiation hardness, would be valuable is in the inner tracking detectors of particle physics experiments. Here, we describe the performance of SiC diodes irradiated in the 24 GeV proton beam at CERN. Schottky measurements have been used to probe the irradiated material for changes in I– V characteristics. Other methods, borrowed from III–V research, used to study the irradiated surface include atomic force microscope scans and Raman spectroscopy. These have been used to observe the damage to the materials surface and internal lattice structure. We have also characterised the detection capabilities of bulk semi-insulating SiC for α radiation. By measuring the charge collection efficiency (CCE) for variations in bias voltage, CCE values up to 100% have been measured.

Operation of irradiation facilities

The operation of a gamma irradiation facility with maximum loading of 18.5×10 15Bq of Coblt60 was undertakan by the shanghai Irradiation Center since 1986 (ref. 1). In the six years of management of gamma facility for multi-purpose uses. the source was almost in continuous operational all years around. The economic gain and the social gain from operation of SIC radiation facility were significient. In this paper, development of the irradiation facility and it operation and relevant R and D are introduced.