Patent Number: 
Section: claims

1. An X-ray detector for detecting X rays, comprising:a semiconductor for generating electric charges therein upon X-ray incidence;electrodes formed on opposite sides of said semiconductor for application of a predetermined bias voltage;a first carrier selection layer formed on said semiconductor at a side of a positive one of said electrodes, that is at a side of an electrode having a higher potential, for restricting an injection of holes; anda second carrier selection layer formed on said semiconductor at a side of a negative one of said electrodes, that is at a side of an electrode having a lower potential, for restricting an injection of electrons;wherein said semiconductor is amorphous selenium (a-Se) doped with a predetermined quantity of an alkali metal or alkaline earth metal in a quantity ranging from 0.01 to 10 ppm. 2. An X-ray detector as defined in claim 1, wherein one of said electrodes formed at an X-ray incidence side is a positive one of said electrodes to which the bias voltage is applied to increase potential. 3. An X-ray detector as defined in claim 2, wherein the quantity of the alkali metal or alkaline earth metal doped is in a range of 0.05 to 2 ppm. 4. An X-ray detector as defined in claim 2, wherein said alkali metal or alkaline earth metal is one of Li, Na, K, and Ca. 5. An X-ray detector as defined in claim 2, wherein said semi-conductor is formed on a TFT substrate having thin film transistor switches, charge storing capacitors and one of said electrodes. 6. An X-ray detector as defined in claim 1, wherein the quantity of the alkali metal or alkaline earth metal doped is in a range of 0.05 to 2 ppm. 7. An X-ray detector as defined in claim 1. wherein said alkali metal or alkaline earth metal is one of Li, Na, K, and Ca. 8. An X-ray detector as defined in claim 1, wherein said semi-conductor is formed on a TFT substrate having thin film transistor switches, charge storing capacitors and one of said electrodes. 9. An X-ray detector for detecting X rays, comprising:a semiconductor for generating electric charges therein upon X-ray incidence;electrodes formed on opposite sides of said semiconductor for application of a predetermined bias voltage;a first carrier selection layer formed on said semiconductor at a side of a positive one of said electrodes, that is at a side of an electrode having a higher potential, for restricting an injection of holes;wherein said semiconductor is amorphous selenium (a-Se) doped with a predetermined quantity of an alkali metal or alkaline earth metal in a quantity ranging from 0.01 to 10 ppm.