Bohumír Zaťko

Spectrometric properties of semi-insulating GaAs detectors irradiated by 5 MeV electrons at different dose rates

The radiation hardness of Semi-Insulating (SI) GaAs detectors against 5 MeV electrons is investigated in this paper. The influence of two parameters, the accumulative absorbed dose (from 1 to 120 kGy) and the applied dose rate (20, 40 or 80 kGy/h), on detector spectrometric properties was studied. The electron irradiation has negatively affected the detector CCE (Charge Collection Efficiency). Un-irradiated detectors exhibited the CCE of 79% at maximum operating reverse voltage of 300 V and reached the maximum CCE of 51% at 200 V after irradiation by a dose of 120 kGy. Relative energy resolution was also affected by electron irradiation. Its global degradation was observed in the range of doses from 24 up to 120 kGy, where an increase from 19% up to 39% at 200 V reverse voltage was noticed. On the other hand, a global increase of detection efficiency with dose, by about 30% at 120 kGy, was observed with all samples. We did not observe any significant influence of chosen dose rates applied during irradiation on investigated spectrometric properties of detectors.

The study of 4H-SiC alpha particle detectors with different Schottky contact metallization

We fabricated and characterized 4H-SiC Schottky diodes as a spectrometric detector of alpha particles. Two types of blocking contacts based on Ni/Au and Pt/Au were used. The total thickness of prepared blocking contacts was about 15 nm to minimize the influence on alpha particles energy resolution. Current-voltage characteristics of two types of detectors were measured at room temperature and compared. As a source of alpha particles we utilized triple radioisotope of 239Pu 241Am 244Cm. Detected alpha particles had energies from 5.1 MeV up to 5.8 MeV. The spectrometric performance of detectors with two types of blocking contacts were evaluated and compared.We fabricated and characterized 4H-SiC Schottky diodes as a spectrometric detector of alpha particles. Two types of blocking contacts based on Ni/Au and Pt/Au were used. The total thickness of prepared blocking contacts was about 15 nm to minimize the influence on alpha particles energy resolution. Current-voltage characteristics of two types of detectors were measured at room temperature and compared. As a source of alpha particles we utilized triple radioisotope of 239Pu 241Am 244Cm. Detected alpha particles had energies from 5.1 MeV up to 5.8 MeV. The spectrometric performance of detectors with two types of blocking contacts were evaluated and compared.

Influence of electron irradiation on properties of semi-insulating GaAs detectors

The effects of electron beam irradiation on electrical and spectrometric properties of semi-insulating (SI) GaAs detectors were studied. The electric properties were monitored by reverse and forward current–voltage characteristics. In general, a breakdown voltage decrease with the dose was observed. However, some samples showed a local increase in the breakdown voltage at doses between 5 and 10 kGy. The detector spectrometric properties (the charge collection efficiency (CCE), the energy resolution and the detection efficiency) were evaluated from measured spectra of the 241Am radionuclide gamma source before and after electron irradiation. The CCE and energy resolution showed minor changes after irradiation. The detection efficiency noticed an initial increase (up to a dose of 5 kGy) followed by a permanent decrease. At 30 kGy, the overall degradation of detector functionality was observed with all samples.

4H-SiC and novel SI GaAs-based M-S-M radiation hard photodetectors applicable in UV, EUV, and soft x-ray detection: design, technology, and performance testing

Work reports on results in development of 4H-SiC and semi-insulating (SI) GaAs large area surface barrier detectors. 4H-SiC detectors are based on high purity liquid phase epitaxy layer with the Schottky barrier contact formed by semitransparent Ni. SI GaAs detectors are based on bulk undoped material using novel electrode metallization with improved sensitivity in UV and soft X-ray ranges. The novel detector use semitransparent low work function Mg metal contact giving a new electronic characteristic of the junction. Electrical characteristics of the diodes, photocurrent measurements and pulse height spectra of gamma and low energy X-rays using the 241Am source, are presented. Improvement of 4H-SiC detector resistance to gamma radiation and neutron fluency is demonstrated. Problems with design and application of related ultra-low noise electronics are introduced and discussed.