BACKGROUND

Radiation detectors may be devices used to measure the flux, spatial distribution, spectrum or other properties of radiations.

Radiation detectors may be used for many applications. One important application is imaging. Radiation imaging is a radiography technique and can be used to reveal the internal structure of a non-uniformly composed and opaque object such as the human body.

Early radiation detectors for imaging include photographic plates and photographic films. A photographic plate may be a glass plate with a coating of light-sensitive emulsion. Although photographic plates were replaced by photographic films, they may still be used in special situations due to the superior quality they offer and their extreme stability. A photographic film may be a plastic film (e.g., a strip or sheet) with a coating of light-sensitive emulsion.

In the 1980s, photostimulable phosphor plates (PSP plates) became available. A PSP plate may contain a phosphor material with color centers in its lattice. When the PSP plate is exposed to radiation, electrons excited by radiation are trapped in the color centers until they are stimulated by a laser beam scanning over the plate surface. As the plate is scanned by laser, trapped excited electrons give off light, which is collected by a photomultiplier tube. The collected light is converted into a digital image. In contrast to photographic plates and photographic films, PSP plates can be reused.

Another kind of radiation detectors are radiation image intensifiers. Components of a radiation image intensifier are usually sealed in a vacuum. In contrast to photographic plates, photographic films, and PSP plates, Radiation image intensifiers may produce real-time images, i.e., do not require post-exposure processing to produce images. Radiation first hits an input phosphor (e.g., cesium iodide) and is converted to visible light. The visible light then hits a photocathode (e.g., a thin metal layer containing cesium and antimony compounds) and causes emission of electrons. The number of emitted electrons is proportional to the intensity of the incident radiation. The emitted electrons are projected, through electron optics, onto an output phosphor and cause the output phosphor to produce a visible-light image.

Scintillators operate somewhat similarly to radiation image intensifiers in that scintillators (e.g., sodium iodide) absorb radiation and emit visible light, which can then be detected by a suitable image sensor for visible light. In scintillators, the visible light spreads and scatters in all directions and thus reduces spatial resolution. Reducing the scintillator thickness helps to improve the spatial resolution but also reduces absorption of radiation. A scintillator thus has to strike a compromise between absorption efficiency and resolution.

Semiconductor radiation detectors largely overcome this problem by direct conversion of radiation into electric signals. A semiconductor radiation detector may include a semiconductor layer that absorbs radiation in wavelengths of interest. When a particle of radiation is absorbed in the semiconductor layer, multiple charge carriers (e.g., electrons and holes) are generated and swept under an electric field towards electric contacts on the semiconductor layer. Cumbersome heat management required in currently available semiconductor radiation detectors (e.g., Medipix) can make a detector with a large area and a large number of pixels difficult or impossible to produce.

SUMMARY

Disclosed herein is a radiation detector comprising: an electronics layer comprising a first set of electric contacts and a second set of electric contacts; a radiation absorption layer configured to absorb radiation; a first set of electrodes and a second set of electrodes, wherein the first set of electrodes and the second set of electrodes are interdigitated and extend into the radiation absorption layer in a direction of thickness thereof; wherein the electronics layer and the radiation absorption layer are bonded such that the first set of electrodes are electrically connected to the first set of electric contacts and the second set of electrodes are electrically connected to the second set of electric contacts.

According to an embodiment, the radiation absorption layer comprises GaAs, CdTe, CZT, or a combination thereof.

According to an embodiment, the first set of electrodes and the second set of electrodes comprise a metal or a semiconductor.

According to an embodiment, the first set of electrodes and the second set of electrodes are configured to be differentially biased.

According to an embodiment, a distance between one of the first set of electrodes to its nearest neighbor of the second set of electrodes does not exceed 2λ, wherein λ is the mean free path of charge carriers in the radiation absorption layer.

According to an embodiment, the second set of electrodes are cylindrical in shape.

According to an embodiment, the second set of electrodes are prismatic in shape.

According to an embodiment, the first set of electrodes comprises a grid.

According to an embodiment, the second set of electrodes are discrete.

According to an embodiment, the first set of electrodes and the second set of electrodes are coextensive in the direction of thickness.

According to an embodiment, the radiation detector further comprises an insulating layer at a surface of the radiation absorption layer distal from the electronics layer; wherein the first set of electrodes and the second set of electrodes are attached to the insulating layer.

According to an embodiment, the radiation absorption layer comprises a polycrystalline semiconductor.

According to an embodiment, the electronics layer is configured to bias the first set of electrodes and the second set of electrodes to different electric voltages through the first set of electric contacts and the second set of electric contacts.

According to an embodiment, the radiation is X-ray.

According to an embodiment, the electronics layer comprises: a first voltage comparator configured to compare a voltage of an electric contact of the second set of electric contacts to a first threshold; a second voltage comparator configured to compare the voltage to a second threshold; a counter configured to register a number of particles of radiation received by the radiation absorption layer; a controller, wherein the controller is configured to start a time delay from a time at which the first voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the first threshold; wherein the controller is configured to activate the second voltage comparator during the time delay; wherein the controller is configured to cause the number registered by the counter to increase by one, upon determination by the second voltage comparator that an absolute value of the voltage equals or exceeds an absolute value of the second threshold.

According to an embodiment, the radiation detector further comprises an integrator electrically connected to the electric contact, wherein the integrator is configured to collect charge carriers from the electric contact.

According to an embodiment, the controller is configured to activate the second voltage comparator at a beginning or expiration of the time delay.

According to an embodiment, the controller is configured to connect the electric contact to an electrical ground.

According to an embodiment, a rate of change of the voltage is substantially zero at expiration of the time delay.

Disclosed herein is a method comprising obtaining a substrate with an insulating layer and a semiconductor layer attached to the insulating layer; forming a first set of electrodes and a second set of electrodes from the semiconductor layer by etching the semiconductor layer through its entire thickness; introducing semiconductor particles among the first set of electrodes and the second set of electrodes; bonding the semiconductor layer with an electronics layer comprising a first set of electric contacts and a second set of electric contacts, such that the first set of electrodes are electrically connected to the first set of electric contacts and the second set of electrodes are electrically connected to the second set of electric contacts.

According to an embodiment, the semiconductor particles comprise GaAs, CdTe, CZT, or a combination thereof.

According to an embodiment, introducing the semiconductor particles among the first set of electrodes and the second set of electrodes comprises fusing the semiconductor particles.

According to an embodiment, the first set of electrodes and the second set of electrodes are configured to be differentially biased.

According to an embodiment, a distance between one of the first set of electrodes to its nearest neighbor of the second set of electrodes does not exceed 2λ, wherein λ is the mean free path of charge carriers across the semiconductor particles.

According to an embodiment, the second set of electrodes are cylindrical in shape.

According to an embodiment, the second set of electrodes are prismatic in shape.

According to an embodiment, the first set of electrodes comprises a grid.

According to an embodiment, the second set of electrodes are discrete.

According to an embodiment, the electronics layer is configured to bias the first set of electrodes and the second set of electrodes to different electric voltages through the first set of electric contacts and the second set of electric contacts.

According to an embodiment, the method further comprises removing the insulating layer.

