CN115826031A - High-purity germanium drift detector - Google Patents
High-purity germanium drift detector Download PDFInfo
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- CN115826031A CN115826031A CN202211435148.9A CN202211435148A CN115826031A CN 115826031 A CN115826031 A CN 115826031A CN 202211435148 A CN202211435148 A CN 202211435148A CN 115826031 A CN115826031 A CN 115826031A
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Abstract
The invention provides a high-purity germanium drift detector, which comprises a main body part, a high-purity germanium drift detector and a high-purity germanium drift detector, wherein the main body part comprises a detector crystal, an amorphous germanium contact layer and an electrode layer, wherein the amorphous germanium contact layer covers the whole surface; the electrode layer comprises a topmost separation electrode group and a bottommost integral electrode, the separation electrode group comprises a charge collection electrode and a plurality of surrounding annular electrodes, the outermost side is a guard ring electrode, and the rest is a drift electrode; the voltage bias part applies positive bias to both the annular electrode and the integral electrode, the absolute value of the voltage applied by the drift electrode is gradually decreased from outside to inside, and the charge collection electrode is positioned at the ground potential; and a signal acquisition processing system. The detector combines the drift detector configuration, the germanium crystal thickness and the amorphous germanium contact process, applies the drift topological structure to the planar high-purity germanium detector based on the amorphous germanium contact, further increases the energy resolution and time performance, greatly expands the detection sensitive area and has higher detection efficiency.
Description
Technical Field
The invention relates to the fields of radiation measurement and X/gamma energy spectrum detection, in particular to a high-purity germanium detector.
Background
The existing silicon drift detector can simultaneously realize large detection area and low capacitance, the energy resolution (FWHM) of the existing silicon drift detector to X-rays can reach <145eV @5.9keV, and the existing silicon drift detector has wide application in the fields of material composition analysis, celestial body physics, nuclear physics and the like. However, due to process limitations, the typical thickness of a silicon drift detector is within 1mm, so that there is a large efficiency loss in the detection of hard X-rays (energy >20 keV). While germanium crystals can easily achieve a crystal thickness of 1mm or more.
A drift detector for high-purity Ge features that the impurity concentration is 10 9 cm -3 To 10 10 cm -3 The high-purity germanium single crystal in the range is a semiconductor detector manufactured by the processes of doping, coating, low-temperature vacuum packaging and the like, and the detector has extremely high energy resolution and higher detection efficiency and is widely used for gamma ray and X-ray measurement. The germanium drift detector has higher detection efficiency, energy resolution and time performance than a silicon drift detector. The prototype development of the germanium drift detector was tried abroad in 1985-1990, but the performance was unsatisfactory due to the technological limit at that time. There has been no report on germanium drift detectors since then.
A major challenge encountered with current high purity germanium drift detectors is the fabrication of finely divided electrodes. In the conventional process, the electrode is manufactured by adopting a Li diffusion or ion implantation mode, the two process modes need to etch a groove with a certain depth between electrodes and then carry out a series of treatments to separate the electrodes, and the process is complex and unstable.
In recent years, germanium crystal coating technologies such as thermal resistance evaporation, electron beam evaporation, magnetron sputtering and the like are widely used for contact manufacturing of detector electrodes, and are mature electrode manufacturing process technologies.
Disclosure of Invention
The invention aims to provide a novel high-purity germanium drift detector so as to obtain better energy resolution, time performance and detection efficiency than a silicon drift detector.
In order to achieve the above object, the present invention provides a high purity germanium drift detector, comprising: a body portion including a detector crystal, an amorphous germanium contact layer covering an entire surface of the detector crystal, and electrode layers disposed at top and bottom of the body portion; the electrode layer comprises a separation electrode group positioned at the topmost part of the main body part and an integral electrode completely covered at the bottommost part of the main body part, and the separation electrode group comprises a charge collecting electrode positioned at the top center of the detector crystal and a plurality of annular electrodes surrounding the charge collecting electrode; the outermost ring electrode is a guard ring electrode, and the plurality of ring electrodes arranged between the charge collection electrode and the guard ring electrode are drift electrodes; a voltage bias part which is arranged to apply positive bias to the annular electrode at the top and the integral electrode at the bottom, the absolute value of the voltage applied by the drift electrode is gradually decreased from outside to inside, the charge collecting electrode at the center is at the ground potential, and the potential of the guard ring electrode is greater than or equal to the potential of the adjacent drift electrode; and a signal acquisition processing system connected with the charge collection electrode.
The amorphous germanium contact layer has a thickness of tens to hundreds of nanometers; the amorphous germanium contact layer is manufactured on the whole surface of the detector crystal in a magnetron sputtering evaporation mode.
The charge collection electrode, drift electrode, and guard ring electrode are rotationally symmetric about a center to increase uniformity of response in all directions of the detector.
The charge collection electrode is circular, and the drift electrode and the guard ring electrode are circular; or the charge collection electrode is square, and the drift electrode and the guard ring electrode are square ring-shaped; or the charge collection electrode is regular hexagonal and the drift electrode and guard ring electrode are regular hexagonal rings.
The thickness of the electrode layer is dozens of nanometers; the electrode layer is manufactured by one of thermal resistance evaporation, electron beam evaporation and magnetron sputtering evaporation.
The signal acquisition and processing system comprises a charge sensitive preamplifier and a data processing system which are sequentially connected with the charge collecting electrode.
The electrode layer is made of aluminum or other common metal conductors.
The material of the detector crystal is P-type or N-type high-purity germanium material.
The invention relates to a manufacturing technology of a high-purity germanium detector, in particular to a germanium drift detector, which innovatively combines the configuration of the drift detector, the thickness of a germanium crystal and a novel amorphous germanium coating process, and applies a drift topological structure to a planar high-purity germanium detector based on amorphous germanium contact. The germanium drift detector may further increase the application of high purity germanium detectors in X/gamma detection. The invention adopts magnetron sputtering evaporation to manufacture amorphous germanium contact, and can obtain satisfactory amorphous germanium contact characteristics by adjusting sputtering parameters such as sputtering pressure, power, gas components and the like. The high-purity germanium drift detector is based on the amorphous germanium contact technology, and can simply and reliably manufacture finely separated electrodes.
Drawings
Fig. 1 is a schematic structural diagram of a germanium drift detector according to an embodiment of the invention, showing cross-section and front topology of the body portion and a voltage bias portion.
Figure 2 is a schematic structural diagram of a body portion of a germanium drift detector according to an embodiment of the present invention, showing a backside topology of the body portion.
Figure 3 is a schematic diagram of a front side topology of a body portion of a germanium drift detector in accordance with an embodiment of the invention.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Fig. 1 shows a germanium drift detector according to an embodiment of the present invention, which includes a body portion 10, a voltage bias portion 20, and a signal acquisition processing system 30.
The body portion 10 includes a detector crystal 11, an amorphous germanium contact layer 12 (shown in black in fig. 1) covering the entire surface of the detector crystal 11, and electrode layers 13 disposed at the topmost and bottommost portions of the body portion 10.
The material of the detector crystal 11 itself is a high purity germanium material (HPGe). The high purity germanium material may be either P-type or N-type. The voltage bias of the electrodes under different material types is different, and the invention is explained by taking the P type as an example. Because the detector crystal 11 is made of germanium material, compared with silicon material used by silicon drift detectors, high-purity germanium has higher atomic number and more excellent carrier migration characteristics, so that the germanium drift detector of the invention has higher detection efficiency, energy resolution and time performance than the silicon drift detector. In the present embodiment, the detector crystal 11 is cylindrical, however, in other embodiments, the detector crystal 11 may be other than cylindrical, such as a rectangular parallelepiped, etc.
The material of the amorphous germanium contact layer 12 is amorphous germanium (a-Ge). Where the amorphous germanium contact layers 12 at the top and bottom of the detector crystal 11 are capable of blocking the injection of electrons or holes (rectifying action like PN junctions), the voltage bias of the electrodes above the amorphous germanium contact layer 12 determines what type of carriers the amorphous germanium contact layer 12 blocks: the positive bias prevents hole injection and the negative bias prevents electron injection. The non-electrode area and the lateral amorphous germanium contact layer 12 then act as a passivation layer to isolate the detector crystal 11 from the outside.
The amorphous germanium contact layer 12 is obtained by uniformly fabricating a layer of amorphous germanium over the entire surface of the detector crystal 11. Specifically, the thickness of the amorphous germanium contact layer 12 is several tens to several hundreds of nanometers, and the amorphous germanium contact layer 12 is formed on the entire surface of the detector crystal 11 by magnetron sputtering evaporation. The process of forming amorphous germanium contact layer 12 is generally divided into two steps, forming amorphous germanium contact layer 12 on the top and side surfaces of detector crystal 11, and then flipping detector crystal 11 to form amorphous germanium contact layer 12 on the bottom surface.
The electrode layer 13 is arranged on the surface of the amorphous germanium contact layer 12. The electrode layer 13 includes a separate electrode group located at the topmost part of the body portion 10, which includes a charge collecting electrode 132 located at the top center of the detector crystal 11 and a plurality of ring electrodes surrounding the charge collecting electrode 132, and an integral electrode 131 completely covering the bottommost part of the body portion 10. The outermost ring electrode is a guard ring electrode 133, and the plurality of ring electrodes disposed between the charge collection electrode 132 and the guard ring electrode 133 are drift electrodes 134.
In this embodiment, the charge collecting electrode 132 may be circular, and the drift electrode 134 and the guard ring electrode 133 are correspondingly circular rings, in other embodiments, the charge collecting electrode 132 may be other shapes such as square, regular hexagon, etc., and the drift electrode 134 and the guard ring electrode 133 are also correspondingly other shapes than circular rings such as square ring, regular hexagon, etc. The charge collection electrode 132, the drift electrode 134, and the guard ring electrode 133 are preferably rotationally symmetric about the center, so as to maximize the uniformity of response within the increased effective detection area.
In the present embodiment, the number of the ring electrodes is 4, and includes 1 guard ring electrode 133 (located at the outermost periphery) and 3 drift electrodes 134, i.e., the separation electrode group includes 5 separated electrodes in total. The outermost guard ring electrode 133 is mainly used to shield the leakage current from the side surface of the detector.
The material of the electrode layer 13 is metal, preferably aluminum. In this embodiment, the material of the electrode layer is aluminum. The electrode layer 13 may be manufactured by one of thermal resistance evaporation, electron beam evaporation, and magnetron sputtering evaporation. The thickness of the electrode layer 13 is several tens of nanometers.
Since the electrode layer 13 on top of the body portion 10, i.e. the separate electrode set, is a separate electrode structure, the separate electrode set is obtained by providing a suitably shaped mask, also in the shape of a ring, for covering areas where no aluminium evaporation is required, on the amorphous germanium contact layer 12 followed by aluminium evaporation. The mask is covered after evaporation of the amorphous germanium contact layer 12.
The electrode layer 13 at the bottom of the body portion 10 (i.e. the integral electrode 131) is obtained by direct evaporation on the amorphous germanium contact layer 12 without the need for a mask.
The process based on amorphous germanium contact allows for simple and reliable fabrication of finely divided electrode layers compared to conventional lithium diffusion and ion implantation processes.
The voltage bias section 20 is configured to: in an operating state, taking a P-type crystal as an example, a positive bias is applied to the guard ring electrode 133, the plurality of drift electrodes 134 and the global electrode 131, and the absolute value of the voltage applied by the drift electrodes 134 gradually decreases from the outside to the inside, the central charge collecting electrode 132 is generally at the ground potential, and the potential of the guard ring electrode 133 is greater than or equal to the potential of the adjacent drift electrode 134.
As shown in fig. 1, taking a P-type high-purity germanium crystal as an example, the bulk electrode 131 is electrically connected to the positive electrode of a power supply, so that a certain positive bias is applied to the bulk electrode 131; in addition, the outermost drift electrode 134 of the plurality of drift electrodes 134 is directly electrically connected to the positive power supply, and the remaining two drift electrodes 134 are electrically connected to the drift electrode 134 outside thereof through a resistor, so that the absolute value of the bias voltage applied to the three front drift electrodes 134 is gradually decreased (from outside to inside) relative to the charge collection electrode 132, thereby forming a lateral drift electric field and fully depleting the crystal. The outermost guard ring electrode 133 applies a bias greater than or equal to the bias of the adjacent drift electrode 134 and generally equal to the positive bias at the global electrode 131. Under this voltage bias, the amorphous germanium contact layer under the global electrode 131 and the drift electrode 134 prevents hole injection, and the amorphous germanium contact layer under the charge collection electrode 132 prevents electron injection.
The signal acquisition and processing system 30 is connected to the charge collection electrode 132 and includes a charge sensitive preamplifier 31 and a data processing system (not shown) connected to the charge collection electrode 132 in turn, so that the electrical signal collected by the charge collection electrode 132 is sent to a subsequent data processing system for processing.
Thus, in operation of the germanium drift detector of the present invention, X-ray photons are generally incident at integral electrode 131 for better uniformity of response. In a sensitive area of the germanium drift detector, photons and a medium generate photoelectric effect or Compton scattering, and positive and negative electron hole pairs are excited. Under the action of the electric field in the sensitive region, the electrons drift toward the bulk electrode 131 and the drift electrode 134 (depending on the generation position of the electrons), and are finally collected; the holes first drift along the radial direction, then drift toward the charge collecting electrode 132 located at the very center, and are finally collected by the charge collecting electrode 132. The induced signal of the charge collecting electrode is then used as the input signal of the charge sensitive preamplifier. Only holes are considered as signal carriers here.
According to the high-purity germanium drift detector, namely the germanium drift detector, the drift topological structure is applied to the planar high-purity germanium drift detector, the relation between junction capacitance and sensitive area is stripped, large detection area and low capacitance can be simultaneously realized, and the low capacitance enables the detector to further realize high energy resolution and high counting rate. High purity germanium crystals with a thickness of 1-10mm can be chosen such that the germanium drift detector has a very satisfactory detection efficiency in the hard X-ray (> 20 keV) band. The amorphous germanium contact process solves the dead zone problem of the high-purity germanium drift detector in the traditional lithium diffusion process and simplifies the process flow. High-purity germanium has excellent carrier mobility characteristics, and the carrier mobility of the high-purity germanium is 1-2 orders of magnitude higher than that of silicon, so that the detector has shorter charge integration time, lower carrier capture and higher counting rate. Compared with the conventional planar high-purity germanium drift detector, the energy resolution of the germanium drift detector is increased by one step, and the germanium drift detector has better detection efficiency and time performance than a silicon drift detector. The germanium drift detector can further increase the application of the high-purity germanium drift detector in X/gamma detection.
Compared with the prior art, the topological structure and the manufacturing process adopted by the germanium drift detector are greatly different, the drift detector configuration, the thickness of the germanium crystal and the novel amorphous germanium coating process are innovatively combined, and the amorphous germanium contact process is utilized to realize the germanium driftAnd moving the detector. One technical difficulty with such amorphous germanium-based contacts is that they can be made to have sufficient resistance (10) 12 Ω) and amorphous germanium of the carrier barrier to make the leakage current of the charge collecting electrode 132 sufficiently small. The invention adopts magnetron sputtering evaporation to manufacture amorphous germanium contact, and can obtain satisfactory amorphous germanium contact characteristics by adjusting sputtering pressure, power and gas components. The high-purity germanium drift detector is based on an amorphous germanium contact process, and can simply and reliably manufacture finely separated electrodes.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and various changes may be made in the above embodiment of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application.
Claims (9)
1. A high purity germanium drift detector, comprising:
a body portion including a detector crystal, an amorphous germanium contact layer covering an entire surface of the detector crystal, and electrode layers disposed at top and bottom of the body portion; the electrode layer comprises a separation electrode group positioned at the topmost part of the main body part and an integral electrode completely covered at the bottommost part of the main body part, and the separation electrode group comprises a charge collecting electrode positioned at the top center of the detector crystal and a plurality of annular electrodes surrounding the charge collecting electrode; the outermost ring electrode is a guard ring electrode, and the plurality of ring electrodes arranged between the charge collection electrode and the guard ring electrode are drift electrodes;
a voltage bias part which is arranged to apply positive bias to both the annular electrode and the integral electrode, wherein the absolute value of the voltage applied by the drift electrode is gradually decreased from outside to inside, the central charge collecting electrode is at the ground potential, and the potential of the guard ring electrode is greater than or equal to the potential of the adjacent drift electrode; and
and the signal acquisition and processing system is connected with the charge collection electrode.
2. The high purity germanium drift detector of claim 1 wherein said amorphous germanium contact layer has a thickness of tens to hundreds of nanometers; the amorphous germanium contact layer is manufactured on the whole surface of the detector crystal in a magnetron sputtering evaporation mode.
3. The high purity germanium drift detector of claim 1 wherein said charge collection electrodes, drift electrodes and guard ring electrodes are rotationally symmetric about a center.
4. The high purity germanium drift detector of claim 3 wherein said charge collecting electrode is circular and said drift and guard ring electrodes are circular; or the charge collection electrode is square, and the drift electrode and the guard ring electrode are square ring-shaped; or the charge collection electrode is regular hexagonal and the drift electrode and guard ring electrode are regular hexagonal rings.
5. The high purity germanium drift detector of claim 1, wherein said electrode layer has a thickness of tens of nanometers; the electrode layer is manufactured by one of thermal electron evaporation, electron beam evaporation and magnetron sputtering evaporation.
6. The high purity germanium drift detector of claim 1 wherein said signal acquisition and processing system comprises a charge sensitive preamplifier and data processing system in series with a charge collection electrode.
7. The high purity germanium drift detector of claim 1, wherein said electrode layer is a metal conductor.
8. The high purity germanium drift detector of claim 7, wherein said electrode layer is aluminum.
9. The high purity germanium drift detector of claim 1 wherein the detector crystal material is a high purity germanium material of P-type or N-type.
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| CN117214942A (en) * | 2023-11-07 | 2023-12-12 | 清华大学 | High-purity germanium detector and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117214942A (en) * | 2023-11-07 | 2023-12-12 | 清华大学 | High-purity germanium detector and preparation method thereof |
| CN117214942B (en) * | 2023-11-07 | 2024-02-09 | 清华大学 | High-purity germanium detector and preparation method thereof |
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