Spectrometric properties of cadmium telluride (CdTe) radiation semiconductor detectors with Schottky-barrier contacts were studied after irradiation with a high energy electron beam of 5 MeV-energy. ...The total cumulative dose of 2.25 kGy was delivered stepwise and the response of detectors to 241Am radioisotope source was acquired using a standard spectrometric chain at reverse bias voltages of 300 V, 400 V and 500 V. To evaluate the radiation damage, the spectral parameters of the 59.5 keV-photopeak were determined, namely the peak position, the full width at half maximum (FWHM), the peak amplitude and the net peak area. The time evolution of these parameters was followed by recording the spectra in 30-seconds (or 2-minutes) intervals after applying the reverse bias voltages. The results demonstrated significant effect of high energy electrons on the spectral characteristics even after applying the lowest dose of 0.5 kGy. The shift of the photopeak to lower energies, the increase of the FWHM and decrease of the peak height and area were confirmed. The time evolution of the observed tendencies disclosed that electron irradiation results in earlier onset of the polarization mechanism. After irradiating with the highest dose of 2.25 kGy, the polarization effect occurs practically immediately after applying the bias voltage.
•CdTe Schottky barrier detectors were fabricated using chips (ACRORAD Co.) of size 4×4×1 mm3 with In/Ti and Pt contacts.•Detectors were irradiated by high energy electron beam (5 MeV) stepwise delivering the total dose from 0.5 up to 2.25 kGy.•Radiation measurements using the 241Am radioisotope source showed 59.5 keV-photopeak shift, FWHM increase, peak height and area decrease already after applying the lowest dose of 0.5 kGy.•Faster onset of the polarization effect after electron irradiation was confirmed.
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•We fabricated α-particle Schottky barrier detectors based on a high-quality 4H-SiC epitaxial layer.•The detectors were tested at temperatures up to 500 °C.•Their reverse current rose ...from 1 pA at room temperature to 10 nA at 500 °C.•Their energy resolution worsened only by 20% compared with that at room temperature.
Industry demand for radiation detectors that work at elevated temperatures is currently growing. Detectors capable of operating at high temperatures are used in harsh environments, such as the nuclear industry, especially thermonuclear or fusion reactors, high-energy physics experiments and space research. We prepared detectors based on a high-quality 50 μm thick 4H-SiC epitaxial layer. The 4H-SiC detector area was defined by an Ni Schottky contact with a diameter of 1 mm. The current–voltage characteristics of the detector measured at room temperature (RT) showed a leakage current of 1 pA at 300 V. The measurement was done at elevated temperatures up to 500 °C, and the leakage current increased to 10 nA. Precise temperature stabilization was achieved using a low-noise self-controlled microcontroller system with a PID loop using ceramic heaters in a customized vacuum chamber. The spectrometric performance of the detector was tested using α-particles generated by 238Pu, 239Pu, 244Cm radioisotopes. The energy resolution of the tested α-particle peaks was about 35 keV at full width at half maximum (FWHM) at RT and increased to 42 keV at a detector temperature of 500 °C. We also observed that the mean energy for the generation of one electron-hole pair changed with temperature. In this article, we push the limits and report on very promising experimental results about a 4H-SiC wide bandgap semiconductor detector operating at very high temperatures.
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•Radiation hardness of three holder types against 5 MeV electrons was investigated.•The holder radiation stability and the detector radiation hardness were compared.•Safe dose limit ...for all holder types was determined to be 500 kGy.•The best radiation stability was achieved by self-made holder from Al2O3 ceramics.
In our radiation hardness studies we observed that SI GaAs detectors irradiated by 5 MeV electrons exhibited different behaviour with applied dose when considering their electrical and spectrometric properties. The detectors were prepared by the same technology using one GaAs wafer differing in the type of holder used to wire-bond the detectors. In this paper the commercially available detector holders together with self-prepared ones were irradiated by 5 MeV electrons under the same conditions as the investigated detectors before. Three types of detector holders were studied to evaluate their radiation hardness: holders prepared on a Printed Circuit Board (PCB), Poly-Vinyl-Chloride (PVC) holders and two different ceramic holders. The best radiation stability was obtained with a holder self-made from aluminium oxide ceramics using gold metallization. The PCB and the PVC holders exhibited similar radiation stability. The most unstable at doses over 500 kGy was the holder made by silk-screen printing technology from ceramics with silver metallization. No significant influence of the dose rate used during irradiation (in the range from 20 to 80 kGy/h) was observed in all types of holders.
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•Functional Schottky barrier diodes based on 4H-SiC epitaxial layer were fabricated.•Typical reverse current of measured 4H-SiC diodes was below 3 pA/mm2.•Estimated Schottky barrier ...height was about 1.30 eV at room temperature.•Capacitance-voltage measurements revealed the doping concentration below 8 × 1013 cm−3.•Energy resolution of 20 keV was reached in detection of α-particles from 238Pu source.
Schottky barrier detectors based on a high-quality 4H-SiC epitaxial layer with varied thickness up to 70 μm were studied. The detectors had front-side circular Ni/Au Schottky contacts and a back-side full-area Ti/Pt/Au ohmic contact. Current-voltage characteristics in the reverse and forward directions of prepared detector structures were measured. The typical reverse current of the detector structure was below 50 pA at room temperature. The Schottky barrier height, series resistance and ideality factor were evaluated from the forward part of the current-voltage characteristics, and they were 1.3 eV, 1.33, and 638 Ω, respectively. Capacitance-voltage measurement of the detectors up to 600 Vwas also realized. This provided data to calculate the depletion width, concentration profile and barrier height. The lowest doping concentration of about 7 × 1013 cm−3 was determined. The spectrometric performance of the Schottky barrier detector structures was analyzed using an α-particle radioisotope source. The detector structures demonstrated a high energy resolution below 20 keV in the full width at half maximum for 5.5 MeV α-particles.
The bulk semi-insulating GaAs material was used for preparation of pad radiation detectors with circular contacts of 1 mm diameter. The spectrometric properties of a semiconductor detector depend on ...the quality of the base material and on the deposited metallization. Another factor affecting the detector spectrometry is the applied bias controlling the electric collection field. With increasing bias, the charge collection efficiency of particular detector grows. However, this spectrometric property should be changing with detector thickness, which affects the intensity of electric collection field at constant bias applied through the detector sandwich structure. In this paper we have studied the electrical and spectrometric properties of semi-insulating GaAs detectors as a function of their thickness. The measured saturation reverse current was in the range of 3 – 30 nA, increasing with decreasing detector thickness at a substrate resistivity of about of 10
7
Ωcm. The maximal obtainable charge collection efficiency evaluated from
241
Am gamma spectra grew with decreasing detector thickness from 50% for a 450 µm thick detector to 80% for a 230 µm thick detector.
The Timepix2-based hybrid-pixel detector with a 500 μm thick silicon sensor was employed for fast-neutrons registration to be applied in neutron radiography of metallic printed circuit heat exchanger ...(PCHE). Two energies of neutrons were experimentally tested. The detection of 3.55 MeV neutrons from the deuteron–deuteron (DD) reaction was compared to 15.7 MeV neutrons from the deuteron–tritium (DT) neutron generator. In order to distinguish the signal induced by the registered neutrons from the accelerator background, filtration of the recorded particle spectral tracks was applied. The benefit of applying hydrogen-based converter layer for 3.55 MeV neutrons was observable. On the other hand, in the case of 15.7 MeV neutrons, the direct registration by interaction with the sensor Si significantly dominates the conversion.
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•The thermally-induced stress of diamond/SiON/GaN was studied by Raman spectroscopy.•SiON positively influenced the thermally-induced stress.•SIMS depth profiling confirmed sharp ...interface at SiON/GaN heterostructure.•H and C atoms were trapped in SiON; thus, they not affect the 2DEG at AlGaN/GaN.
The effect of silicon oxynitride (SiON) layer on the thermally-induced stress of diamond-coated AlGaN/GaN heterostructures was studied by Raman and SIMS spectroscopy. Diamond films (0.8 or 2.8 µm in thickness) were grown by MWCVD on selected areas of AlGaN/GaN/Si substrates with SiON interlayer. The stress in diamond became tensile for the thinner strip in the range of 0 ÷ 0.5 GPa and compressive for the thicker strip in the range of −0.6 ÷ −0.1 GPa both measured at temperatures ranging from 50 to 400 °C. The applied SiON interlayer positively influenced the induced stress (Δstress decreased by about 0.14 GPa compared to the sample without SiON) independently on the thickness of the diamond film. SIMS depth profiling was applied to analyse the influence of diamond CVD on the AlGaN/GaN interface of SiON passivated samples. As observed, the hydrogen and carbon atoms were trapped in the SiON which acted as a stop layer.
The particle detector based on a low concentration 4H-SiC epitaxial layer shows promising properties for the detection of various types of ionizing radiation. The wide bandgap energy of the 4H-SiC ...semiconductor material (3.23 eV at room temperature) allows the detector to operate reliably at room temperature and at elevated temperatures up to several hundred degrees Celsius. The 80 >m thick 4H-SiC epitaxial layer grown on a 350 >m 4H-SiC substrate was used for detector preparation. The active area of the detector was defined by a 3 mm Schottky contact. The current-voltage measurement shows a reverse current of less than 30 pA up to 1000 V. Capacitance-voltage measurements show that the epitaxial layer is completely depleted at bias voltages above 250 V. The detector has been tested with neutrons of energies from 370 keV up to 14.9 MeV. Neutrons were produced by three nuclear reactions p-T, d-D and d-T. The measured spectra clearly identified the elastic and inelastic scattering at silicon and carbon atoms of detector material.
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•The outstanding spectrometry with bulk SI GaAs detector was published.•The suitability of SI GaAs detectors for digital radiography was shown.•The evaluation of developed imaging ...systems based on SI GaAs detectors was made.•The functional SI GaAs sensor for Timepix chip was presented.
Our research in the field of bulk SI (semi-insulating) GaAs detectors for digital imaging has taken almost 20 years. We have optimized the process of detector fabrication and improved the detector quality in terms of its detection properties. We have obtained the energy resolution of 7.2% for 122 keV photons decreased to 5.3% by cooling the detector to 255 K. The typical charge collection efficiency of our SI GaAs detectors is between 85 and 88%. Besides, we were developing various X-ray imaging systems. We started with moving one single detector, where we obtained a spatial resolution of 500 µm but the exposition period was of several hours. Later we prepared a digital X-ray scanner composed of 480 strip detectors in one line scanning an area of 12 × 15 cm2 and obtaining the spatial resolution of 250 µm. This fully homemade scanner shortened the exposition time to several minutes. Finally we have fabricated a two-dimensional system of 256 × 256 pixel SI GaAs detectors covering an area of 1.4 × 1.4 cm2 suitable for Timepix read-out chip developed by the MEDIPIX2 collaboration reaching a basic spatial resolution of 55 µm and exposition in the range of not more than a few seconds.
A radiation hardness study of semi-insulating GaAs detectors against 5 MeV electrons is presented in this paper. The influence of cumulative dose in the range from 136 up to 2000 kGy on ...alpha-spectrometry of 241Am is evaluated for investigated detectors. The characterising parameter, the charge collection efficiency, was negatively affected by cumulative dose applied. At 200 V detector reverse bias it rapidly decreased from initial 45% it to 15% at 600 kGy proceeding with mild deterioration down to 6% at2000 kGy. The operability of detector was well preserved through whole range of doses. The alpha- and gamma-spectrometry of the same radioactive source are compared.
