Multi-Functional Semiconductor Detector
Multi-Functional Semiconductor Radiation Detector
Tech Area / Field
- FIR-INS/Nuclear Instrumentation/Fission Reactors
- FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors
- INS-DET/Detection Devices/Instrumentation
3 Approved without Funding
Institute of Physical-Technical Problems, Russia, Moscow reg., Dubna
- Russian Academy of Sciences / Institute of Radioengineering and Electronics / Fryazino Branch, Russia, Moscow reg., Fryazino\nRussian Academy of Sciences / Physical Technical Institute, Russia, St Petersburg
- Health Canada / Healthy Environments and Consumer Safety Branch, Canada, ON, Ottawa\nHelsinki Institute of Physics, Finland, Helsinki\nUniversity of Glasgow / Department of Physics and Astronomy, UK, Glasgow\nUniversità degli Studi di Firenze / Department of Energy, Italy, Florence
Project summaryThe goal of the project is designing and fabrication of linear dual-energy x-ray detectors based on GaAs epitaxial structures. Such detectors make it possible to ensure the acquisition of two images with different effective x-ray energy with single exposure. So one can acquire images of materials with low-Z and high-Z simultaneously. Dual-energy x-ray detector is well suited to medical applications. It can be applied also in non-destructive control of objects containing the substances with strongly distinguishing atomic numbers. The dual-energy x-ray detector made of the single semiconductor material will consist of two linear x-ray detectors. The “thick” (with great absorption length) detector produces high energy photon image whereas the “thin” detector allows to get the low energy x-ray photon image. Both detectors are placed in the same plane, so it is possible to choose the different effective energy of incident x-rays for each detector by the use of different filters or by the use of different spectral sensitivity of detectors.
Dual energy x-ray detectors to be developed in the frame of this project must have the following advantages compared to x-ray detectors made of the pair of different semiconductor materials:
- X-ray detector has a flat form, so it is easier to fabricate;
- X-ray detector has more simple construction and thus lower fabrication cost;
- Dual-energy detector makes it possible to form configuration well suited for given application.
The linear x-ray semiconductor detectors, in which the direct conversion of energy of x-ray photons to an electrical signal occurs, enable to get the x-ray images, which are not disturbed by the x-rays, scattered from tested object. It gives the possibility to boost the quality of image considerably without the use of additional resorts.
Large areas can be covered in a single recording scan, what makes it possible to avoid undesirable effects created by the penumbra of x-ray radiation.
New type of x-ray detectors based on epitaxial GaAs structures was developed in the Institute of Radio engineering and Electronics of Russian Academy of Sciences. These detectors operate in photovoltaic mode without reverse bias that enables almost completely elimination of detector noise arising due to leakage current. The epitaxial GaAs structures were grown by vapor phase epitaxy technique on heavy doped substrates. The epitaxial structure consists of three layers: p+-GaAs top layer, n-GaAs active layer and n+-GaAs buffer layer. The ohmic contacts were prepared by vacuum deposition of Al/Cr and Au/Ge films upon the: p+-GaAs epitaxial layer and onto rear side of substrate n+-GaAs respectively.
The sensitivity of GaAs photovoltaic detector was measured by the use of bremsstrahlung radiation from the x-ray tube with tungsten anode in the range of effective energies from 8 KeV up to 120 KeV. The short-circuit current was registered as signal. A maximum response of the detector operating in short circuit mode was obtained at 35 KeV and was 30 μA·min/Gy·cm2. The response of the detector varies linearly with the x-ray intensity.
On the base of photovoltaic GaAs x-ray detectors were fabricated linear and bilinear x-ray detectors with the different spatial resolution for digital radiography. Using of a grazing incident angle geometry (“on-edge” technique) which provides larger absorption length for x-ray photons without increasing of the actual thickness of n-GaAs layer leads to increasing of quantum efficiency for detection of high energy x-ray photons.
Present project offers a new level of development of x-ray detectors for digital radiography. It is stimulated by the last achievements of Institute of Radio engineering and Electronics of RAS in field of epitaxial growth of GaAs structures and development semiconductor devices for various applications.
The realization of project goals will be pided in four stages (two quarters each).
The first stage includes improving of the technology of epitaxial grows GaAs structures, control and selection epitaxial GaAs structures suitable for fabrication of x-ray detectors. Simultaneously will be planned the development of measuring equipment and methods of fabrication discrete spectrometric and pixel photovoltaic detectors based on GaAs structures for energy range 8-120 keV.
The second stage is design and fabrication of linear x-ray detectors for low and high energies, investigations of spectrometric and radiometric and dosimeter detector parameters, creation of low-noise read-out electronics and investigations of methods of x-ray bremsstrahlung spectrum formation to obtain necessary energetic sensitivity of x-ray detectors.
The third stage is the development and the test of construction of detector modules for low and high x-ray energies, development, fabrication and testing of spectrometric block for detection of x- and γ-rays. Test of dosimeters fabricated on the base GaAs photovoltaic structures is supposed too.
The forth stage is the fabrication and test of dual-energy x-ray detectors.
During preparation of work under the Project as the organizations-collaborators a number of the interested organizations offers on partnership or cooperation will be made of the countries - founders of the International Scientific and technical Center (ISTC). As such organizations we shall specify: the Human Monitoring Laboratory, Health Canada; Helsinki Institute of Physics, University of Glasgow and a number of others.