F. Dubecky

Detector of fast neutrons based on silicon carbide epitaxial layers

High quality liquid phase epitaxial layer of 4H-SiC with a thickness of 105 μm was used for fabrication of detector with the circular Schottky contact formed by using Au/Ni double layer contact metallization. The detector structure was characterized by current-voltage measurements showing low reverse current density at room temperature. Following the detection of fast neutrons was studied using the 239Pu-Be source with the mean neutron energy of about 4 MeV. Detected spectrum revealed silicon and carbon-recoil ion continuum. The simulation of detection efficiency vs. thickness of the detector active layer shows linear dependence.

Semi-insulating GaAs radiation detectors: PICTS study of neutron-induced defects

Influence of damage by neutrons introduced in semi-insulating GaAs detectors is studied by current-voltage measurement and Photo-Induced Current Transient Spectroscopy (PICTS). Significant rise of the reverse current is observed at neutron fluencies exceeding 10¹³ ncm⁻². The PICTS is used for evaluation of deep-level states in detector structures prior and after neutron bombardment. Formation of a new significant neutron-induced acceptor-like deep level with apparent energy position (E<inf>C</inf>-E<inf>t</inf>) 1.02 eV was observed for fluencies >10¹³ ncm⁻².

First results observed with test X-CT system using GaAs radiation detector working in single photon counting regime

The aim of present work is application of novel single photon counting system for detection of gamma-rays in CT using semiconductor radiation detector based on semi-insulating (SI) GaAs compound. A simple positioning test system consisting of two stepper motors with 241 Am gamma source of 60 keV photons and single SI GaAs radiation detector operated in single photon counting mode is used for taking CT projections. First, rather preliminary results of CT reconstruction applied to imaging of inner structure of a small phantom using developed reconstruction algorithms is demonstrated

Surface barrier 4H-SiC soft X-ray detecor for hot plasmas diagnostic

The work reports on the characterization of high purity epitaxial 4H-SiC grown by liquid phase epitaxy and the performances of Au-Ni/4H-SiC detectors fabricated on the same material. X-ray diffraction and topography as well as I-V, C-V and DLTS measurements are used for the evaluation of the material properties and device characteristics. The X-ray detection abilities are evaluated by pulse-height spectra measurements of the 241Am. Preliminary results of the detector hardness to fast neutron and gamma ray radiations are also reported.

Influence of active volume on detection efficiency of GaAs neutron detectors

The semi-insulating (SI) GaAs detectors prepared from bulk LEC (Liquid Encapsulated Czochralski) substrate polished down from both sides to 270 μm were tested as detectors of fast neutrons. The HDPE (High Density PolyEthylene) neutron converter layer was applied on the Schottky electrode using PP (PolyPropylene) glue. The influence of the detector active volume (modified via different reverse voltage applied) on the detection efficiency was studied using 239Pu-Be source of fast neutrons. The obtained experimental results were in agreement with the simulation predictions carried out using Monte Carlo radiation transport computer code MCNPX (Monte Carlo N-Particle eXtended).

Detection of soft X-rays using semi-insulating GaAs detector

This work deals with the performance of thin semi-insulating GaAs-based detectors of ionizing radiation DC-coupled to the low noise readout electronics. Fabricated detector have square shape Ti/Pt/Au Schottky blocking contact with dimension of 0.5 mm and full area AuGeNi eutectic alloy quasi-ohmic contact on the opposite site. The current-voltage characteristic and 241Am pulse-height spectra of the detectors were measured and evaluated. The best energy resolution of 6.7 % for 59.5 keV gamma photons was achieved at lowered temperature of 255 K. The detector and the first stage of preamplifier (JFET) was cooled using one stage Peltier cooler.

Particle detectors based on 4H-SiC epitaxial layer and their properties

We fabricated and characterized 4H-SiC Schottky diodes as a spectrometric detector of a-particles. A Schottky contact of Ni/Au of 1.4 mm in diameter was used. Current-voltage characteristics of the detector were measured and a current density lower than 25 nAcm⁻² was observed at room temperature. A ²²⁶Ra used as a source of a-particles within the energy range between 4.6 MeV and 7.7 MeVfor detector testing. The energy resolution below 48 keV was measured for 7.7 MeV a-particles. The detector was irradiated by ¹³² Xe²³⁺ ions with energy of 165 MeV and fluencies of 5×10⁹ cm ² and 1.5× 10¹⁰ cm². Spectra of α-particles were measured after irradiation and significant degradation of energy resolution was observed.

Investigation of metal contacts on semi-insulating GaAs: Physics, technology and applications

The work reports on a study of the symmetric metal/SI GaAs/metal (M-S-M) diodes in order to demonstrate the effect of contact metal work function. We compare the high work function Pt contact versus the low work function Mg contact. The Pt-S-Pt, Mg-S-Mg and Mg-S-Pt structures are characterized by the current-voltage measurements. The Mg-S-Pt structure show a significant current decrease at low bias while the Mg-S-Mg structure shows saturation current at high voltages more than an order of magnitude lower with respect to the Pt-S-Pt reference. The phenomena observed in Mg-containing samples are explained by the presence of insulating MgO layer at the M-S interface. The reported findings have potential applications in sensors based on SI GaAs.

Metal/SI GaAs/Metal systems: Demonstration of unpinning of the Fermi level at the interface

The work reports on the study of metal/semi-insulating GaAs/metal systems with different contacts: Mg, Gd, In and AuGeNi eutectic. Charge carrier transport through the interface is characterized by the current-voltage measurements. Observed results: i) opposite generally accepted “ohmic, bulk limited” charge transport at low bias, ii) are in contradiction with the thermionic emission model of charge transport in M-SI GaAs, and iii) demonstrate the unpinning of the Fermi level at the M-SI GaAs interface.

Application of single-crystal CVD diamond and SiC detectors for diagnostics of ion emission from laser plasmas

The application of single-crystal CVD diamond and SiC detectors for the measurement of ions generated from laser-produced plasmas is reported. It was found that detectors are mostly sensitive to fast ions and protons. Optimization of the diagnostic system based on the detectors is discussed.