Radiation detector
View Patent ↗The radiation detector according to this invention has a common electrode for bias voltage application formed on a surface of an amorphous selenium semiconductor film (a-Se semiconductor film) sensitive to radiation. The common electrode is a gold thin film having a thickness in a range of 100 to 1,000 Å. The gold thin film acting as the common electrode may be formed on the surface of the a-Se semiconductor film at a relatively low vapor deposition temperature and in a reduced vapor deposition time. This feature suppresses a generation of defects in the a-Se semiconductor film due to formation of the common electrode. The gold thin film for the common electrode is not so thick as in the prior art, but is 1,000 Å or less. With the reduced thickness, the common electrode has improved boding property with respect to the a-Se semiconductor film.
1. A radiation detector having an amorphous selenium semiconductor film sensitive to radiation, and a common electrode for bias voltage application formed two-dimensionally on a front surface of the radiation sensitive amorphous selenium semiconductor film, electric charges being generated in the radiation sensitive amorphous selenium semiconductor film upon incidence of radiation to be detected, with a bias voltage applied to the common electrode:
wherein said common electrode comprises a gold thin film (Au thin film) having a thickness of 100 to 1,000 angstroms.
2. A radiation detector as defined in claim 1 , wherein said gold thin film has a thickness in a range of 450 to 550 angstroms.
3. A radiation detector as defined in claim 1 , further comprising a carrier selective intermediate layer formed between said amorphous selenium semiconductor film and said common electrode.
4. A radiation detector as defined in claim 3 , wherein, when a positive bias voltage is applied to said common electrode, said carrier selective intermediate layer is formed of a material having a contribution of electrons larger than a contribution of holes.
5. A radiation detector as defined in claim 3 , wherein, when a negative bias voltage is applied to said common electrode, said carrier selective intermediate layer is formed of a material having a contribution of holes larger than a contribution of electrons.
6. A radiation detector as defined in claim 3 , wherein said intermediate layer has a thickness in a range of 0.1 to 10 μm.
7. A radiation detector as defined in claim 3 , wherein said intermediate layer is one of a polycrystalline semiconductor such as Sb 2 S 3 , ZnTe, CeO 2 , CdS, ZnSe or ZnS, and an amorphous semiconductor of selenium or selenium compound doped with an alkali metal such as Na, a halogen such as Cl, As or Te.
8. A radiation detector as defined in claim 1 , further comprising:
a plurality of collecting electrodes formed in a one-dimensional or two-dimensional matrix arrangement set to a radiation detection effective area; and
a carrier selective intermediate layer formed between said amorphous selenium semiconductor film and said collecting electrodes.
9. A radiation detector as defined in claim 8 , wherein, when a positive bias voltage is applied to said common electrode, said carrier selective intermediate layer is formed of a material having a contribution of holes larger than a contribution of electrons.
10. A radiation detector as defined in claim 8 , wherein, when a negative bias voltage is applied to said common electrode, said carrier selective intermediate layer is formed of a material having a contribution of electrons larger than a contribution of holes.
11. A radiation detector as defined in claim 8 , wherein said intermediate layer has a thickness in a range of 0.1 to 10 μm.
12. A radiation detector as defined in claim 8 , wherein said intermediate layer is one of a polycrystalline semiconductor such as Sb 2 S 3 , ZnTe, CeO 2 , CdS, ZnSe or ZnS, and an amorphous semiconductor of selenium or selenium compound doped with an alkali metal such as Na, a halogen such as Cl, As or Te.
13. A radiation detector as defined in claim 1 , further comprising an active matrix substrate, said active matrix substrate including:
a plurality of collecting electrodes formed on a surface of the active matrix substrate, in a one-dimensional or two-dimensional arrangement set within a radiation detection effective area; and
an electric circuit arranged on the active matrix substrate for storing and reading electric charges collected by the respective collecting electrodes;
said amorphous selenium semiconductor film being stacked on the surface, where the collecting electrodes are formed, of the active matrix substrate.
14. A radiation detector as defined in claim 13 , wherein said collecting electrodes are formed of one of copper, aluminum, nickel and indium tin oxide.
15. A radiation detector as defined in claim 13 , further comprising:
a gate driver for applying read signals for reading the electric charges collected by said collecting electrodes;
charge-to-voltage converting amplifiers for amplifying the electric charges read;
a multiplexer for switching connections for reading; and
an analog-to-digital converter for digitizing amplified electric charges into radiation detection signals;
said gate driver, said charge-to-voltage converting amplifiers, said multiplexer and said analog-to-digital converter being connected as separate, external devices to said active matrix substrate.
16. A radiation detector as defined in claim 13 , further comprising:
a gate driver for applying read signals for reading the electric charges collected by said collecting electrodes;
charge-to-voltage converting amplifiers for amplifying the electric charges read;
a multiplexer for switching connections for reading; and
an analog-to-digital converter for digitizing amplified electric charges into radiation detection signals;
certain or all of said gate driver, said charge-to-voltage converting amplifiers, said multiplexer and said analog-to-digital converter being mounted in said active matrix substrate.
17. A radiation detector as defined in claim 1 , further comprising an active matrix substrate, said active matrix substrate including:
a collecting electrode formed on a surface of the active matrix substrate and set within a radiation detection effective area; and
an electric circuit arranged on the active matrix substrate for storing and reading electric charges collected by the collecting electrode;
said amorphous selenium semiconductor film being stacked on the surface, where the collecting electrode is formed, of the active matrix substrate;
said active matrix substrate being a non-array type.
18. A radiation detector as defined in claim 1 , wherein said amorphous selenium semiconductor film is one of high purity amorphous selenium (a-Se), and an amorphous semiconductor of selenium or selenium compound doped with an alkali metal such as Na, a halogen such as Cl, As or Te.
19. A radiation detector as defined in claim 1 , wherein said amorphous selenium semiconductor film has a thickness in a range of 0.5 to 1.5 mm.