Semiconductor radiation detector

Abstract

Disclosed herein is a radiation detector (100), comprising: an electronics layer (120) comprising a first set of electrical contacts (118A) and a second set of electrical contacts (118B); a radiation absorbing layer (110) configured to absorb radiation; a semiconductor substrate (103), a portion of the semiconductor substrate (103) extending into the radiation absorbing layer (110) along its thickness direction, the portion forming a first set of electrodes (119A) and a second set of electrodes (119B); wherein the first set of electrodes (119A) and the second set of electrodes (119B) interdigitate with each other; wherein the semiconductor substrate (103) comprises a p-n junction separating the first set of electrodes (119A) from the second set of electrodes (119B); wherein the electronics layer (120) and the semiconductor substrate (103) are bonded such that the first set of electrodes (119A) is electrically connected to the first set of electrical contacts (118A), and the second set of electrodes (119B) is electrically connected to the second set of electrical contacts (118B).

Description

[Background Technology]

[0001] A radiation detector is a device that measures properties of radiation. Examples of these properties may include the spatial distribution of the radiation's intensity, phase, and polarization. The radiation may be radiation that has interacted with an object. For example, the radiation measured by a radiation detector may be radiation that has penetrated or reflected from an object. The radiation may be electromagnetic radiation, such as infrared light, visible light, ultraviolet light, X-rays, or gamma rays. Radiation may also be of other types, such as alpha and beta rays.

[0002] One type of radiation detector is based on the interaction between radiation and semiconductors. For example, this type of radiation detector may have a semiconductor layer that absorbs radiation and generates charge carriers (e.g., electrons and holes) and a circuit for detecting the charge carriers.

[0003] Cadmium zinc telluride (CdZnTe or Cd 1-x Zn x Te) is a direct-gap semiconductor and an excellent candidate for room-temperature radiation detection. Cadmium zinc telluride is an alloy of zinc telluride and cadmium telluride (CdTe), where the x value is the molar concentration of zinc in the CdZnTe. CdZnTe, with an x value ranging from 0.04 to 0.2, is considered a promising material for detector development because it can process and improve certain properties of CdTe. For example, both CdTe and CdZnTe have large atomic numbers, which gives the material excellent braking power, resulting in high absorption efficiency for incident X-rays and gamma rays; and has a large band gap (e.g., 1.5eV-1.6eV), which can be used in room-temperature detectors; it also has a high resistivity to achieve a good signal-to-noise ratio for radiation detectors. At the same time, due to the incorporation of zinc, CdZnTe has a larger band gap than CdTe, thereby increasing the maximum achievable resistivity.

[0004] Practical uses of CdTe and CdZnTe detectors cover a wide range of applications, such as medical and industrial imaging, industrial metrology and non-destructive testing, security and surveillance, nuclear safeguards and non-proliferation, and astrophysics. [Summary of the invention]

[0005] Disclosed herein is a radiation detector comprising: an electronic device layer comprising a first set of electrical contacts and a second set of electrical contacts; a radiation absorbing layer configured to absorb radiation; a semiconductor substrate, a portion of the semiconductor substrate extending into the radiation absorbing layer along its thickness direction, the portion forming a first set of electrodes and a second set of electrodes; wherein the first set of electrodes and the second set of electrodes intersect with each other; wherein the semiconductor substrate comprises a pn junction separating the first set of electrodes from the second set of electrodes; wherein the electronic device layer and the semiconductor substrate are combined such that the first set of electrodes is electrically connected to the first set of electrical contacts, and the second set of electrodes is electrically connected to the second set of electrical contacts.

[0006] According to an embodiment, the radiation absorbing layer includes gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof.

[0007] According to an embodiment, the first set of electrodes and the second set of electrodes are configured to be differentially biased.

[0008] According to an embodiment, the distance between one electrode of the first set of electrodes and the nearest neighboring electrode of the second set of electrodes does not exceed 2λ, where λ is the mean free path of charge carriers in the radiation absorbing layer.

[0009] According to an embodiment, the second set of electrodes are cylindrical.

[0010] According to an embodiment, the second set of electrodes are prismatic.

[0011] According to an embodiment, the first set of electrodes comprises a grid.

[0012] According to an embodiment, the second set of electrodes are discrete.

[0013] According to an embodiment, the first set of electrodes and the second set of electrodes are coextensive in the thickness direction.

[0014] According to an embodiment, the pn junction has discrete parts.

[0015] According to an embodiment, the pn junction is located at an interface between a first doped semiconductor region of the semiconductor substrate and a second doped semiconductor region of the semiconductor substrate.

[0016] According to an embodiment, the first doped semiconductor region surrounds the second doped semiconductor region.

[0017] According to an embodiment, the second doped semiconductor region is in electrical contact with the second set of electrodes.

[0018] According to an embodiment, the first doped semiconductor region extends from a surface of the semiconductor substrate to an interface between the radiation absorbing layer and the semiconductor substrate.

[0019] According to an embodiment, the second doped semiconductor region is coextensive with the first doped semiconductor region.

[0020] According to an embodiment, the radiation absorbing layer includes a polycrystalline semiconductor.

[0021] According to an embodiment, the electronics layer is configured to bias the first and second sets of electrodes to different voltages through the first and second sets of electrical contacts.

[0022] According to an embodiment, said radiation is X-rays.

[0023] According to an embodiment, the electronic device layer includes: a first voltage comparator, which is configured to compare the electrical contact voltage of the second group of electrical contacts with a first threshold; a second voltage comparator, which is configured to compare the voltage with a second threshold; a counter, which is configured to record the number of radiation particles received by the radiation absorption layer; a controller, wherein the controller is configured to start a time delay when it is determined from the first voltage comparator that the absolute value of the voltage is equal to or exceeds the absolute value of the first threshold; wherein the controller is configured to start the second voltage comparator during the time delay; wherein the controller is configured to increase the number recorded by the counter by one if the second voltage comparator determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold.

[0024] According to an embodiment, the radiation detector further comprises an integrator electrically connected to the electrical contact, wherein the integrator is configured to collect charge carriers from the electrical contact.

[0025] According to an embodiment, the controller is configured to activate the second voltage comparator at the beginning or end of the time delay.

[0026] According to an embodiment, the controller is configured to connect the electrical contact to electrical ground.

[0027] According to an embodiment, the rate of change of the voltage is substantially zero at the end of the time delay.

[0028] Disclosed herein is a method comprising forming a first set of electrodes and a second set of electrodes from a semiconductor substrate by etching the substrate partially through its thickness; forming a first doped semiconductor region in the semiconductor substrate; forming a second doped semiconductor region in the semiconductor substrate; introducing semiconductor particles between the first set of electrodes and the second set of electrodes to form a radiation absorbing layer; joining the semiconductor substrate to an electronic device layer comprising a first set of electrical contacts and a second set of electrical contacts such that the first set of electrodes is electrically connected to the first set of electrical contacts and the second set of electrodes is electrically connected to the second set of electrical contacts; wherein the first doped semiconductor region and the second doped semiconductor region form a pn junction separating the first set of electrodes from the second set of electrodes.

[0029] According to an embodiment, the semiconductor particles include gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof.

[0030] According to an embodiment, introducing the semiconductor particles between the first set of electrodes and the second set of electrodes comprises melting the semiconductor particles.

[0031] According to an embodiment, the first set of electrodes and the second set of electrodes are configured to be differentially biased.

[0032] According to an embodiment, the distance between one electrode of the first set of electrodes and the nearest neighboring electrode of the second set of electrodes does not exceed 2λ, where λ is the mean free path of charge carriers in the radiation absorbing layer.

[0033] According to an embodiment, the second set of electrodes are cylindrical.

[0034] According to an embodiment, the second set of electrodes are prismatic.

[0035] According to an embodiment, the first set of electrodes comprises a grid.

[0036] According to an embodiment, the second set of electrodes are discrete.

[0037] According to an embodiment, the electronics layer is configured to bias the first and second sets of electrodes to different voltages through the first and second sets of electrical contacts.

[0038] According to an embodiment, the first doped semiconductor region surrounds the second doped semiconductor region.

[0039] According to an embodiment, the second doped semiconductor region is in electrical contact with the second set of electrodes.

[0040] According to an embodiment, the first doped semiconductor region extends from a surface of the semiconductor substrate to an interface between the radiation absorbing layer and the semiconductor substrate.

[0041] According to an embodiment, the second doped semiconductor region is coextensive with the first doped semiconductor region.

[0042] According to an embodiment, etching the semiconductor substrate is by wet etching, dry etching or a combination thereof.

[0043] According to an embodiment, the semiconductor substrate includes silicon, germanium, gallium arsenide, or a combination thereof.

Brief Description of the Drawings

[0044] Figure 1A A cross-sectional view of a radiation detector according to an embodiment is schematically shown.

[0045] Figure 1B A detailed cross-sectional view of the radiation detector according to an embodiment is schematically shown.

[0046] Figure 1C-1E Each schematically illustrates a suitable configuration of the first set of electrodes and the second set of electrodes of the radiation detector according to an embodiment.

[0047] Figure 2A and Figure 2B Each diagram schematically shows an electronic system component of the radiation detector according to an embodiment.

[0048] Figure 3 Schematically illustrating the temporal variation of the current flowing through an electrical contact (upper curve) caused by carriers generated by a visible light pulse incident on a pixel associated with the electrical contact, and the corresponding temporal variation of the voltage (lower curve) according to an embodiment.

[0049] Figures 4A-4F A flow chart schematically illustrates a method for manufacturing the radiation detector according to an embodiment.

[0050] Figure 5-Figure 9 Each schematically illustrates a system comprising a radiation detector as described herein. [Specific implementation method]

[0051] Figure 1A A schematic diagram illustrates an overall cross-sectional view of a radiation detector 100 according to an embodiment. The radiation detector 100 may include a semiconductor substrate 103, a radiation absorbing layer 110 configured to absorb radiation, and an electronics layer 120 (e.g., an application-specific integrated circuit) for processing or analyzing an electrical signal generated in the radiation absorbing layer 110 in response to incident radiation. In an embodiment, the radiation detector 100 does not include a scintillator. The radiation absorbing layer 110 may include a polycrystalline semiconductor material, such as gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the radiation energy of interest. The radiation may be X-rays.

[0052] like Figure 1B As shown in the detailed cross-sectional view of the radiation detector 100 according to an embodiment, a portion of the semiconductor substrate 103 extends into the radiation absorbing layer 110 along its thickness direction (Th), thereby forming a first group of electrodes 119A and a second group of electrodes 119B that intersect each other. The first group of electrodes 119A and the second group of electrodes 119B may be coextensive in the thickness direction (Th) of the radiation absorbing layer 110. The semiconductor substrate 103 has a pn junction that separates the first group of electrodes 119A from the second group of electrodes 119B. That is, each electrical path between the first group of electrodes 119A and the second group of electrodes 119B and completely inside the semiconductor substrate 103 passes through the pn junction. The pn junction may be located at the interface between the first doped semiconductor region 117A of the semiconductor substrate 103 and the second doped semiconductor region 117B of the semiconductor substrate 103. The second doped semiconductor region 117B may be in electrical contact with the second group of electrodes 119B. As Figure 1BAs shown in the example in , the pn junction may have discontinuous parts. That is, the pn junction may not be a spatially continuous junction.

[0053] The first doped semiconductor region 117A may surround the second doped semiconductor region 117B. The second doped semiconductor region 117B need not be centered in the first doped semiconductor region 117A. The first doped semiconductor region 117A may extend from the surface 103A of the semiconductor substrate 103 to the interface 110A between the radiation absorbing layer 110 and the semiconductor substrate 103. The second doped semiconductor region 117B may be coextensive with the first doped semiconductor region 117A, for example, in a direction perpendicular to the semiconductor substrate 103.

[0054] like Figure 1B As shown, when a radiation particle strikes the radiation absorbing layer 110, the radiation particle may be absorbed by the radiation absorbing layer 110, and the radiation absorbing layer 110 may generate one or more carriers through several mechanisms. One radiation particle may generate 10 to 100,000 carriers. The carriers may drift toward the first set of electrodes 119A and the second set of electrodes 119B under an electric field. The electric field may be established by differentially biasing the first set of electrodes 119A and the second set of electrodes 119B. According to an embodiment, the distance between one electrode in the first set of electrodes 119A and the nearest electrode in the second set of electrodes 119B (e.g., Figure 1B The distance 104 in the radiation absorbing layer 110 does not exceed 2λ, where λ is the mean free path of carriers in the radiation absorbing layer 110.

[0055] like Figures 1C-1E As shown in the example of FIG, the first set of electrodes 119A and the second set of electrodes 119B can have any suitable size and shape. Figure 1C In the embodiment (e.g., in Figure 1D In the embodiment (e.g., in Figure 1E ), the first set of electrodes 119A comprises a grid and at least some of the electrodes in the second set of electrodes are discrete.

[0056] The electronics layer 120 may include an electronics system 121 suitable for processing or interpreting signals generated by radiation incident on the radiation absorbing layer 110. The electronics system 121 may include analog circuits such as filter networks, amplifiers, integrators, and comparators, or digital circuits such as microprocessors and memory. The electronics system 121 may be electrically coupled to the radiation absorbing layer 110 via vias 131. The spaces between the vias may be filled with a filler material 130, which may increase the mechanical stability of the connection between the electronics layer 120 and the radiation absorbing layer 110. Other bonding techniques may be used to connect the electronics system 121 to the radiation absorbing layer 110 without the use of vias.

[0057] The electronics layer 120 has a first set of electrical contacts 118A and a second set of electrical contacts 118B. After combining the electronics layer 120 and the radiation absorbing layer 110, the first set of electrodes 119A can be electrically connected to the first set of electrical contacts 118A (via vias 131), and the second set of electrodes 119B can be electrically connected to the second set of electrical contacts 118B (e.g., via vias 131). The electronics layer 120 can be configured to bias the first set of electrodes 119A and the second set of electrodes 119B to different voltages via the first set of electrical contacts 118A and the second set of electrical contacts 118B, respectively. For example, one or more voltage sources 122 can provide a non-zero voltage to the first set of electrical contacts 118A, and the second set of electrical contacts 118B can be connected to a virtual ground of an amplifier in the electronics system 121.

[0058] In an embodiment, the pn junction is under reverse bias during operation of the radiation detector 100. This reverse bias can be used to establish an electric field between the second set of electrodes 119B and the first set of electrodes 119A. The pn junction under reverse bias substantially blocks current flow through the pn junction, but allows current to flow between the second set of electrodes 119B and the electronics layer 120 through the second doped semiconductor region 117B.

[0059] Figure 2A and Figure 2B Each diagram shows a component of the electronic system 121 according to an embodiment. The electronic system 121 may include a first voltage comparator 301 , a second voltage comparator 302 , a counter 320 , a switch 305 , a voltmeter 306 , and a controller 310 .

[0060] The first voltage comparator 301 is configured to compare the voltage of an electrical contact of the second set of electrical contacts 118B with a first threshold value. The first voltage comparator 301 can be configured to monitor the voltage directly or calculate the voltage by integrating the current flowing through the electrical contact over a period of time. The first voltage comparator 301 can be controllably activated or deactivated by the controller 310. The first voltage comparator 301 can be a continuous comparator. That is, the first voltage comparator 301 can be configured to be continuously activated and continuously monitor the voltage. The first voltage comparator 301 can be a clocked comparator, which has the advantage of lower power consumption. The first threshold value can be 5-10%, 10%-20%, 20-30%, 30-40%, or 40-50% of the maximum voltage that a single visible light pulse can generate at the electrical contact. The maximum voltage can depend on the energy of the incident radiation particle, the material of the radiation absorbing layer 110, and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV or 200 mV.

[0061] The second voltage comparator 302 is configured to compare the voltage with a second threshold value. The second voltage comparator 302 can be configured to directly monitor the voltage or to calculate the voltage by integrating the current flowing through the electrical contacts over a period of time. The second voltage comparator 302 can be a continuous comparator. The second voltage comparator 302 can be controllably activated or deactivated by the controller 310. When the second voltage comparator 302 is deactivated, the power consumption of the second voltage comparator 302 can be less than 1%, less than 5%, less than 10% or less than 20% of the power consumption when the second voltage comparator 302 is activated. The absolute value of the second threshold value is greater than the absolute value of the first threshold value. As used herein, the term "absolute value" or "modulus" |x| of a real number x is a non-negative value of x regardless of its sign. That is, The second threshold value may be 200%-300% of the first threshold value. The second threshold value is at least 50% of the maximum voltage that an incident radiation particle can generate on one of the electrical contacts in the second set of electrical contacts 118B. For example, the second threshold value may be 100 mV, 150 mV, 200 mV, 250 mV, or 300 mV. The second voltage comparator 302 and the first voltage comparator 301 may be the same component. That is, the electronic system 121 may have the same voltage comparator that can compare the voltage to two different threshold values at different times.

[0062] The first voltage comparator 301 or the second voltage comparator 302 may include one or more operational amplifiers or any other suitable circuits. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the electronic system 121 to operate under a high flux of incident radiation particles. However, having a high speed usually comes at the expense of power consumption.

[0063] The counter 320 is configured to record at least a number of radiation particles received by the radiation absorbing layer 110 (e.g., radiation particles generated by carriers collected by a subset of the first set of electrodes 119A and a subset of the second set of electrodes 119B). The counter 320 can be a software component (e.g., a number stored in a computer memory) or a hardware component (e.g., a 4017 IC and a 7490 IC).

[0064] The controller 310 can be a hardware component, such as a microcontroller or microprocessor. The controller 310 is configured to initiate a time delay when the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold (e.g., when the absolute value of the voltage increases from an absolute value below the first threshold to an absolute value equal to or exceeding the first threshold). Absolute value is used here because voltage can be negative or positive. The controller 310 can be configured to disable the second voltage comparator 302, the counter 320, and any other circuitry not required for the operation of the first voltage comparator 301 until the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The time delay can terminate before or after the voltage becomes stable (i.e., the rate of change of the voltage is substantially zero). The phrase "rate of change is substantially zero" means that the temporal rate of change of the voltage is less than 0.1% / ns. The phrase "rate of change is substantially non-zero" means that the temporal rate of change of the voltage is at least 0.1% / ns.

[0065] The controller 310 may be configured to activate the second voltage comparator during the time delay (including the start and end). In an embodiment, the controller 310 is configured to activate the second voltage comparator at the start of the time delay. The term "activate" means to put a component into an operating state (e.g., by sending a signal such as a voltage pulse or logic level, by providing power, etc.). The term "deactivate" means to put a component into a non-operating state (e.g., by sending a signal such as a voltage pulse or logic level, by cutting off power, etc.). The operating state may have higher power consumption than the non-operating state (e.g., 10 times higher, 100 times higher, 1000 times higher). The controller 310 itself may be deactivated until the output of the first voltage comparator 301 activates the controller 310 when the absolute value of the voltage equals or exceeds the absolute value of the first threshold.

[0066] If the second voltage comparator 302 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold during the time delay, the controller 310 may be configured to increase the number recorded by the counter 320 by one.

[0067] The controller 310 can be configured to cause the optional voltmeter 306 to measure the voltage at the end of the time delay. The controller 310 can be configured to connect the electrical contact 118B to electrical ground to reset the voltage and discharge any carriers accumulated on the electrical contact 118B. In an embodiment, the electrical contact 118B is connected to electrical ground after the end of the time delay. In an embodiment, the electrical contact 118B is connected to electrical ground for a limited reset period. The controller 310 can connect the at least one electrical contact 119B to the electrical ground by controlling the switch 305. The switch can be a transistor such as a field effect transistor (FET).

[0068] In an embodiment, the electronic system 121 has no analog filter network (eg, RC network). In an embodiment, the electronic system 121 has no analog circuitry.

[0069] The voltmeter 306 may feed the measured voltage to the controller 310 in the form of an analog or digital signal.

[0070] The electronic system 121 may include an integrator 309 electrically connected to the electrical contact 118B, wherein the integrator is configured to collect carriers from the electrical contact 118B. The integrator 309 may include a capacitor in the feedback path of the amplifier. An amplifier configured in this way is called a capacitive transimpedance amplifier (CTIA). A capacitive transimpedance amplifier has a high dynamic range by preventing the amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. The carriers from the electrical contact 118B accumulate on the capacitor over a period of time ("integration period"). After the integration period ends, the capacitor voltage is sampled and then reset by a reset switch. The integrator 309 may include a capacitor directly connected to the electrical contact 118B.

[0071] Figure 3 The diagram schematically illustrates the temporal variation of current flowing through electrical contact 118B caused by carriers generated by radiation particles (upper curve) and the corresponding temporal variation of the voltage at electrical contact 118B (lower curve). The voltage may be the integral of the current with respect to time. At time t0, the radiation particles impact the radiation absorbing layer 110, carriers begin to be generated in the radiation absorbing layer 110, current begins to flow through electrical contact 118B, and the absolute value of the voltage at electrical contact 118B begins to increase. At time t1, the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1. The controller 310 initiates time delay TD1 and may deactivate the first voltage comparator 301 at the start of TD1. If the controller 310 was deactivated before time t1, it is activated at time t1. During TD1, the controller 310 activates the second voltage comparator 302. As used herein, the term "during" a time delay means the beginning and the end (i.e., the end) and any time in between. For example, the controller 310 may start the second voltage comparator 302 at the end of TD1. If, during TD1, the second voltage comparator 302 determines that the absolute value of the voltage at time t2 is equal to or exceeds the absolute value of the second threshold value V2, the controller 310 waits for the voltage to stabilize. The voltage at time t e Stable, at this time all carriers generated by the radiation particles drift out of the radiation absorbing layer 110. s , the time delay TD1 ends. At time t e At or after the time of the digitization, the controller 310 causes the voltmeter 306 to digitize the voltage and determine in which bin the energy of the radiation particle falls. The controller 310 then causes the counter 320 corresponding to the bin to increase the number by one. Figure 3 In the example, the time t sAt the time t e That is, TD1 ends after all carriers generated by the radiation particles drift out of the radiation absorbing layer 110. If the time t cannot be easily measured e , TD1 can be selected empirically to allow sufficient time to collect substantially all of the carriers generated by the radiation particle, but TD1 cannot be too long, otherwise there is a risk that carriers generated by another incident radiation particle will be collected. That is, TD1 can be selected empirically so that time t s At time t e After that. Time t s Not necessarily at time t e Afterwards, since once V2 is reached, the controller 310 may ignore TD1 and wait for time t e Therefore, the rate of change of the difference between the voltage and the dark current contribution to the voltage at time t e The controller 310 may be configured to disable the second voltage comparator 302 at the end of TD1 or at time t2 or any time therebetween.

[0072] At time t e The voltage of is proportional to the number of charge carriers generated by the radiation particle, which is related to the energy of the radiation particle. The controller 310 may be configured to use the voltmeter 306 to determine the energy of the radiation particle.

[0073] After TD1 expires or is digitized by the voltmeter 306 (whichever is later), the controller connects the electrical contact 118B to electrical ground for a reset period RST to allow carriers accumulated on the electrical contact 119B to flow to ground and reset the voltage. After the reset period RST, the electronic system 121 is ready to detect another incident radiation particle. If the first voltage comparator 301 is disabled, the controller 310 can activate it at any time before the reset period RST expires. If the controller 310 is disabled, it can be activated before the reset period RST expires.

[0074] Figures 4A-4F A method for manufacturing the radiation detector 100 according to an embodiment is schematically illustrated. Figure 4A and Figure 4BThe schematic diagram shows that the first group of electrodes 119A and the second group of electrodes 119B are formed by partially etching the entire thickness of the semiconductor substrate 103. In an embodiment, the semiconductor substrate is etched by wet etching, dry etching, or a combination thereof. As shown in the previous example, the first group of electrodes 119A may or may not have the same shape or structure as the second group of electrodes 119B. The first group of electrodes 119A may include a grid, and the second group of electrodes 119B may be discrete. The second group of electrodes 119B may be cylindrical or prismatic. In an embodiment, the distance between one electrode in the first group of electrodes 119A and the nearest electrode in the second group of electrodes 119B (e.g., Figure 4B The distance 104 in the radiation absorbing layer 110 does not exceed 2λ, where λ is the mean free path of carriers in the radiation absorbing layer 110.

[0075] Figure 4C The schematic diagram shows a first doped semiconductor region 117A and a second doped semiconductor region 117B formed in the semiconductor substrate 103. The first doped semiconductor region 117A and the second doped semiconductor region 117B form a pn junction that separates the second set of electrodes 119B from the rest of the semiconductor substrate 103. The first doped semiconductor region 117A may surround the second doped semiconductor region 117B. The second doped semiconductor region 117B may be in electrical contact with the second set of electrodes 119B. The second doped semiconductor region 117B may be formed by doping a portion of the first doped semiconductor region 117A. The first doped semiconductor region 117A may be formed by doping the semiconductor substrate 103 with p-type or n-type dopants. The first doped semiconductor region 117A may extend from the surface 103A of the semiconductor substrate 103 to the interface 110A between the radiation absorbing layer 110 and the semiconductor substrate 103. The second doped semiconductor region 117B may be coextensive with the first doped semiconductor region 117A. The second doped semiconductor region 117B may be formed by doping the semiconductor substrate 103 with a p-type or n-type dopant, and the dopant used is opposite to the dopant used to form the first doped semiconductor region 117A. For example, if the first doped semiconductor region 117A is formed by doping the semiconductor substrate 103 with a p-type dopant, the second doped semiconductor region 117B may be formed by doping the semiconductor substrate 103 with an n-type dopant, and vice versa.

[0076] Figure 4DThe schematic diagram shows the introduction of semiconductor particles 116 into the space between the first set of electrodes 119A and the second set of electrodes 119B. For example, the space can be filled with a slurry containing semiconductor particles 116 distributed in a fluid, which is later removed. The semiconductor particles 116 can include gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof. The semiconductor particles 116 can include other suitable semiconductors. In one example, introducing the semiconductor particles 116 between the first set of electrodes 119A and the second set of electrodes 119B includes melting the semiconductor particles 116. After melting, at least some of the semiconductor particles 116 can become polycrystalline semiconductors. After melting, voids may still exist between the semiconductor particles 116. In embodiments, the melted semiconductor particles 116 do not need to be coextensive with the first set of electrodes 119A and the second set of electrodes 119B in the thickness direction.

[0077] Figure 4E The semiconductor substrate 103 , including the first set of electrodes 119A, the second set of electrodes 119B and the radiation absorbing layer 110 , is schematically shown bonded to an electronics layer 120 .

[0078] Figure 4F The schematic diagram shows that after bonding, the first set of electrodes 119A is electrically connected to the first set of electrical contacts 118A, and the second set of electrodes 119B is electrically connected to the second set of electrical contacts 118B. In an embodiment, the first set of electrodes 119A and the second set of electrodes 119B are configured to be differentially biased by the electronics layer 120 via the first set of electrical contacts 118A and the second set of electrical contacts 118B. Multiple chips can be bonded to the same electronics layer 120, where each chip includes the radiation absorbing layer 110.

[0079] The radiation detector 100 described above may be used in various systems, such as the system provided below.

[0080] Figure 5 A system 9000 including the radiation detector 100 described herein is schematically illustrated. The system can be used for medical imaging, such as chest radiography, abdominal radiography, and the like. The system includes a radiation source 1201. Radiation emitted from the radiation source 1201 penetrates an object 1202 (e.g., a human body part such as the chest, limbs, or abdomen), is attenuated to varying degrees by the internal structures of the object 1202 (e.g., bones, muscles, fat, and organs), and is projected onto the system 9000. The system 9000 forms an image by detecting the intensity distribution of the radiation.

[0081] Figure 6A system 9000 including the radiation detector 100 described herein is schematically shown. The system can be used for medical imaging, such as dental radiography. The system includes a radiation source 1301. Radiation emitted from the radiation source 1301 penetrates an object 1302 that is part of the oral cavity of a mammal (e.g., a human). The object 1302 may include the maxilla, the upper jaw, teeth, the mandible, or the tongue. The radiation is attenuated to varying degrees by different structures of the object 1302 and is projected onto the system 9000. The system 9000 forms an image by detecting the intensity distribution of the radiation. Teeth absorb more radiation than caries, infections, or the periodontal ligament. The radiation dose received by dental patients is typically very small (approximately 0.150 mSv for a full-mouth series).

[0082] Figure 7 A schematic diagram illustrates a cargo scanning or non-intrusive inspection (NII) system 9000 that includes the radiation detector 100 described herein. The system can be used for luggage inspection at public transportation stations or airports. The system includes a radiation source 1501. Radiation emitted from the radiation source 1501 can penetrate a piece of luggage 1502, where it is attenuated to varying degrees by the luggage's contents and projected onto the system 9000. The system 9000 forms an image by detecting the intensity distribution of the transmitted radiation. The system can reveal the contents of luggage and identify prohibited items on public transportation, such as firearms, narcotics, sharp objects, and flammable items.

[0083] Figure 8 A schematic diagram illustrates a whole-body scanner system 9000 including the radiation detector 100 described herein. The whole-body scanner system 9000 can detect metallic or non-metallic objects on a person for security inspection without physically removing clothing or making physical contact. The whole-body scanner system includes a radiation source 1601. Radiation emitted from the radiation source 1601 can be backscattered from a person 1602 being inspected and objects thereon and projected onto the system 9000. The objects and the person can backscatter radiation differently. The system 9000 forms an image by detecting the intensity distribution of the backscattered radiation. The radiation source 1601 of the system 9000 can be configured to scan a person in a linear or rotational direction.

[0084] Figure 9A radiation computed tomography (radiation CT) system 9000 is schematically illustrated. The radiation CT system uses computer-processed radiation to generate tomographic images (virtual "slices") of specific regions of a scanned object. These tomographic images can be used for diagnostic and therapeutic purposes in various medical disciplines, as well as for flaw detection, failure analysis, metrology, assembly analysis, and reverse engineering. The radiation CT system includes the radiation detector 100 and radiation source 1701 described herein. The radiation detector 100 and radiation source 1701 can be configured to rotate synchronously along one or more circular or spiral paths.

[0085] The radiation detector 100 described herein may also have other applications, such as radiation telescopes, mammography, industrial radiation defect detection, radiation microscopy or radiation micrography, radiation casting inspection, radiation non-destructive testing, radiation weld inspection, radiation digital subtraction angiography, etc. It may be suitable to use the system 9000 in place of a photographic plate, photographic film, a photoexcitable phosphor plate, a radiation image intensifier, a scintillator, or another semiconductor radiation detector.

[0086] Although various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for illustrative purposes only and are not intended to be limiting, and their true scope and spirit should be determined by the claims herein.

Claims

1. A radiation detector comprising: an electronics layer comprising a first set of electrical contacts and a second set of electrical contacts; a radiation absorbing layer configured to absorb radiation; a semiconductor substrate, a portion of the semiconductor substrate extending into the radiation absorbing layer along a thickness direction of the semiconductor substrate, the portion forming a first set of electrodes and a second set of electrodes; wherein the first group of electrodes and the second group of electrodes intersect each other; wherein the semiconductor substrate includes a pn junction separating the first set of electrodes from the second set of electrodes; wherein the electronic device layer and the semiconductor substrate are bonded such that the first set of electrodes are electrically connected to the first set of electrical contacts, and the second set of electrodes are electrically connected to the second set of electrical contacts. 2 . The radiation detector of claim 1 , wherein the radiation absorbing layer comprises gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof. 3 . The radiation detector of claim 1 , wherein the first set of electrodes and the second set of electrodes are configured to be differentially biased.

4. The radiation detector of claim 1, wherein a distance between one electrode in the first set of electrodes and a nearest neighboring electrode in the second set of electrodes does not exceed 2λ, where λ is a mean free path of carriers in the radiation absorbing layer. The radiation detector of claim 1 , wherein the second set of electrodes are cylindrical. The radiation detector of claim 1 , wherein the second set of electrodes are prismatic in shape. The radiation detector of claim 1 , wherein the first set of electrodes comprises a grid.

8. The radiation detector of claim 1, wherein the second set of electrodes are discrete.

9. The radiation detector of claim 1, wherein the first set of electrodes and the second set of electrodes are coextensive in the thickness direction.

10. The radiation detector of claim 1, wherein the pn junction has discrete portions. 11 . The radiation detector of claim 1 , wherein the pn junction is located at an interface between a first doped semiconductor region of the semiconductor substrate and a second doped semiconductor region of the semiconductor substrate. 12 . The radiation detector of claim 11 , wherein the first doped semiconductor region surrounds the second doped semiconductor region.

13. The radiation detector of claim 11, wherein the second doped semiconductor region is in electrical contact with the second set of electrodes. 14 . The radiation detector of claim 11 , wherein the first doped semiconductor region extends from a surface of the semiconductor substrate to an interface between the radiation absorbing layer and the semiconductor substrate.

15. The radiation detector of claim 11, wherein the second doped semiconductor region is coextensive with the first doped semiconductor region.

16. The radiation detector of claim 1, wherein the radiation absorbing layer comprises a polycrystalline semiconductor.

17. The radiation detector of claim 1, wherein the electronics layer is configured to bias the first and second sets of electrodes to different voltages through the first and second sets of electrical contacts.

18. The radiation detector of claim 1, wherein the radiation is X-rays.

19. The radiation detector according to claim 1, Wherein the electronic device layer comprises: a first voltage comparator configured to compare an electrical contact voltage of the second set of electrical contacts to a first threshold; a second voltage comparator configured to compare the voltage to a second threshold; a counter configured to record the number of radiation particles received by the radiation absorbing layer; a controller, wherein the controller is configured to initiate a time delay when the absolute value of the voltage is determined from the first voltage comparator to be equal to or greater than the absolute value of the first threshold; wherein the controller is configured to enable the second voltage comparator during the time delay; The controller is configured to increase the number recorded by the counter by one if the second voltage comparator determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold.

20. The radiation detector of claim 19, further comprising an integrator electrically connected to the second set of electrical contacts, wherein the integrator is configured to collect carriers from the electrical contacts.

21. The radiation detector of claim 19, wherein the controller is configured to enable the second voltage comparator at the beginning or end of the time delay.

22. The radiation detector of claim 19, wherein the controller is configured to connect the second set of electrical contacts to electrical ground.

23. The radiation detector of claim 19, wherein the rate of change of the voltage is substantially zero at the end of the time delay.

24. A method of manufacturing a radiation detector, comprising: forming a first set of electrodes and a second set of electrodes from the semiconductor substrate by etching the semiconductor substrate partially through a thickness thereof; forming a first doped semiconductor region in the semiconductor substrate; forming a second doped semiconductor region in the semiconductor substrate; introducing semiconductor particles between the first set of electrodes and the second set of electrodes to form a radiation absorbing layer; bonding the semiconductor substrate to an electronic device layer including a first set of electrical contacts and a second set of electrical contacts such that the first set of electrodes is electrically connected to the first set of electrical contacts and the second set of electrodes is electrically connected to the second set of electrical contacts; The first doped semiconductor region and the second doped semiconductor region form a pn junction separating the first set of electrodes from the second set of electrodes.

25. The method of claim 24, wherein the semiconductor particles comprise gallium arsenide, cadmium telluride, cadmium zinc telluride, or a combination thereof.

26. The method of claim 24, wherein introducing the semiconductor particles between the first set of electrodes and the second set of electrodes comprises melting the semiconductor particles.

27. The method of claim 24, wherein the first set of electrodes and the second set of electrodes are configured to be differentially biased.

28. The method of claim 24, wherein the distance between an electrode in the first set of electrodes and the nearest neighboring electrode in the second set of electrodes does not exceed 2λ, where λ is the mean free path of charge carriers in the radiation absorbing layer.

29. The method of claim 24, wherein the second set of electrodes are cylindrical.

30. The method of claim 24, wherein the second set of electrodes are prismatic in shape.

31. The method of claim 24, wherein the first set of electrodes comprises a grid.

32. The method of claim 24, wherein the second set of electrodes are discrete.

33. The method of claim 24, wherein the electronics layer is configured to bias the first and second sets of electrodes to different voltages through the first and second sets of electrical contacts. The method of claim 24 , wherein the first doped semiconductor region surrounds the second doped semiconductor region.

35. The method of claim 24, wherein the second doped semiconductor region is in electrical contact with the second set of electrodes.

36. The method of claim 24, wherein the first doped semiconductor region extends from a surface of the semiconductor substrate to an interface between the radiation absorbing layer and the semiconductor substrate.

37. The method of claim 24, wherein the second doped semiconductor region is coextensive with the first doped semiconductor region.

38. The method of claim 24, wherein etching the semiconductor substrate is by wet etching, dry etching, or a combination thereof.

39. The method of claim 24, wherein the semiconductor substrate comprises silicon, germanium, gallium arsenide, or a combination thereof.

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