RU236141U1 - HIGH-SPEED DETECTOR BASED ON WIDE-BAND SEMICONDUCTOR MATERIAL FOR REGISTRATION OF PULSED X-RAY RADIATION - Google Patents

Abstract

The utility model relates to semiconductor devices for converting ionizing radiation into an electrical signal, the measurement of which makes it possible to determine the radiation level and the accumulated dose of pulsed X-ray radiation. A high-speed detector based on a wide-gap semiconductor material for recording pulsed X-ray radiation is a pin detector containing a sensitive element with a p+/i/n+ structure, placed in an SPPD11-xx housing. The sensitive element is made in the form of a pin structure produced by the method of gas-phase epitaxy from organometallic compounds at reduced pressure and temperatures, containing a GaAs substrate consisting of: an i-GaAs layer; an n+-GaAs layer; a continuous Pt/TiN/Ag contact; a p+-GaAs layer; a Ti/Pd/Au metallization layer; a polyamide layer. The technical result of the utility model is an increase in the detector response time by 1.5-2 times and an increase in the amplitude of the useful signal by 1.5-3 times. 3 fig.

Description

The main advantage of a high-speed detector based on a wide-band semiconductor material for recording pulsed X-ray radiation is high resistance to radiation loads. Their disadvantages include unsatisfactory spatial resolution, which does not allow them to be used in beam positioning systems or flat image recognition.

Field of technology

The utility model relates to semiconductor devices for converting ionizing radiation into an electrical signal, the measurement of which allows determining the radiation level and the accumulated dose of pulsed X-ray radiation. In particular, the utility model relates to the technology of recording ionizing radiation, in particular to pulsed X-ray radiation detectors, which are a p-i-n detector intended for use in various radiation level measurement systems, dosimeters, background excess indicators and radiometers, including for individual monitoring of radioactive exposure and for warning of radioactive hazard, as well as in medical diagnostics.

State of the art

Semiconductor sensitive elements based on p-i-n detectors have become widely used as devices for recording pulsed X-ray radiation with high resolution. Their operating principle is based on the fact that when an ionizing particle passes through the detector, the charge induced in the detector substance is collected on the electrodes.

An important feature of semiconductor detectors is their small dimensions. This has greatly expanded the possibilities of using such detectors not only in the field of physical experiments, but also in technology - in process control devices and in medicine.

The technical problem of the claimed utility model is to ensure the possibility of using a sensitive element in terms of electrical parameters and overall dimensions in the housings of detectors of the SPPD11-xx type.

It is known from the state of the art that the closest to the claimed utility model is a silicon sensitive element (utility model of the Russian Federation RU 140489 U1). The produced sensitive elements of pulsed X-ray radiation based on semiconductor silicon provide a response speed of 1.5-2 ns, which limits their use in solving modern problems of nuclear and radiation physics.

It is proposed to manufacture a detector based on gallium arsenide with a high threshold sensitivity and a low noise level (patent RU 2307426 C1). This is achieved due to the design, which allows to convert the energy of particles or quanta of ionizing radiation into nonequilibrium electron-hole pairs, accumulate and store the charge and non-destructively read information about the accumulated charge during accumulation in the external circuit. However, an insulating layer of Ga _1-x Al _x As is introduced into the design, having a common boundary with the GaAs-GaAs layer, containing a substrate in contact with it, a semi-insulating arsenide-gallium layer and a barrier contact. The insulating layer of Ga _1-x Al _x As and the said barrier contact are placed on the semiconductor layer of undoped gallium arsenide, then in the undoped layer of GaAs and the insulating layer of gallium-aluminum arsenide until the semi-insulating layer of GaAs forms a local region of p-type conductivity and a region with high resistance surrounding the periphery of the contact barrier. The proposed design of the device allows accumulating and storing the information charge, eliminates the contribution of the components of thermal and shot noise inherent in resistive detectors in the current reading mode, which allows significantly increasing the threshold sensitivity and energy resolution of the sensor. However, due to the small size of the cell, such a design is effective only for the case of a matrix organization of the detector.

In the work UA 8064 A gallium arsenide epitaxial p/i/n diode structures are obtained from the liquid phase. This method provides obtaining a diode structure with a pn junction breakdown voltage of 100-1500 V and a reverse recovery time of 20-200 nsec under measurement conditions at a forward current density of 50 A/ ^cm2 and a forward current decay rate of 200 A/μs at a maximum permissible junction temperature of +260°C.

The disadvantage of the method is the difficulty of implementation on an industrial scale, since most operations allow for a large amount of defective products.

A GaAs detector with a p+/i/n+ structure is manufactured by growing a substrate with a certain doping (patent US 20040069213 A1), after which the substrate is polished to reduce its thickness to 10 µm. Then annealing is carried out, as a result of which a p+/i/n+ structure is formed. The next step is to make ohmic contacts on both sides. This step is followed by masking, and then the etching process.

The advantage of the method is that this detector can be used to detect photons whose energy is in the range between 20 and 60 keV.

The disadvantage of the method is the use of the lithography method, as well as the additional minimal introduction of defects in order to have a minor impact on the characteristics of the detector, where the power of one of the detector pixels will be measured in relation to the radiation dose.

The GaAs detector (patent WO 9635236 A1) comprises: a) a monocrystalline high-resistivity coating layer (LTG) having a trapping density of more than 10 ^cm3 , said layer being applied to at least one side of a GaAs wafer over a GaAs surface, preferably by molecular beam epitaxial growth (MBE) with molecular flows of Ga and As at a reduced wafer temperature to form a highly non-stoichiometric layer having a maximum thickness of 20 nm.

The advantage of this method is the achievement of improved performance in terms of charge capture for the detection of α-particles with an energy of 5.48 MeV from Am241 and between 85 and 93% for a detector with a thickness of 200 μm. Due to the mirror-symmetric arrangement of the electrodes and the use of a capping layer for α-particles, an energy resolution of less than 6 _W is achieved, as well as in the reduction of loss currents at the interface and on the surface. In addition, the radiation hardness of the GaAs detector no longer depends on the radiation hardness of the capping layer, as in the case of _SiO2 or _Si3N4 , but only on the radiation hardness of the original GaAs material. This is due to the use of a capping layer made of the same GaAs material as the base material. This embodiment is particularly suitable for cases where serial production of a detector with very thin active parts should be possible.

The disadvantage of the method is the additional thermal treatment of the metallization layer, which has already been evaporated, in order to achieve the necessary reduction in the energy barrier at the interface between the metallization and GaAs.

A p-i-n GaAs structure (patent RU 2610388 C2) with p, i and n regions in one epitaxial layer is obtained simultaneously during the epitaxy process during the growth of a high-resistance i-region, limited on both sides by lightly doped p- and n-regions using a developed cooling mode, which allows the formation of the required carrier concentration distribution profile in the base region of the structure without an additional increase in the growth gap between the substrates. diodes using standard methods of photolithography, etching, sputtering and contact annealing.

The advantage is that the technical result achieved by implementing the developed method consists in reducing the forward voltage drop of the GaAs p-i- n structure while simultaneously reducing the reverse recovery time. The structure's response speed increases, since a large accumulation charge accumulates in thick, lightly doped p- and n-regions during the forward current flow due to the high density of minority charge carriers, and this increases the reverse recovery time and, consequently, worsens the diode dynamics. The method allows significantly improving, compared to the closest analogue, the main technical parameters of GaAs p-i-n structures.

The disadvantage of this method is the production of a doped p-i-n structure of GaAs, as well as the use of lithography in the manufacturing process.

A method for the simultaneous production of a pin structure of GaAs having p-, i- and n-regions in one epitaxial layer (patent RU 2488911), comprising heating the initial batch to form a saturated melt solution of its components, the interaction of the melt solution with the components to obtain a given composition of the melt solution, contacting the substrate with the obtained melt solution, subsequent forced cooling to grow an epitaxial layer of GaAs having a pin structure, removing the substrate covered with a GaAs layer having a pin structure from under the melt, wherein the component compositions of the melt solutions for growing the GaAs pin structure are formed in a dehydrated atmosphere by preliminary introducing into the initial batch in certain quantities at least two additional solid components, which are silicon dioxide SiO ₂ and gallium oxide (III), followed by heating this multicomponent batch to the epitaxy onset temperature and holding at this temperature for a pre-set time.

The disadvantage of the known method can be recognized as the high forward voltage drop of the resulting GaAs p-i-n structure with a simultaneous significant reverse recovery time.

GaAs (WO 201420112) is created using a well-known but little-used method of growing semiconductor crystals from the vapor phase - low-pressure hydride phase epitaxy (LP-HVPE) to produce GaAs with unique properties of ultra-long free-carrier lifetime. This method improves the state of the art of semiconductor materials for various applications including high-resolution radiation detectors, significantly improves material quality, and is scalable for the production of large quantities and aperture sizes.

The advantage of the method is that LP-HVPE GaAs with a high free carrier lifetime has the potential to have a major impact in the field of semiconductor radiation detectors, providing a high energy resolution material that can operate at room temperature. These vapor-grown crystals will be more reproducible and easier to grow (and therefore cheaper) than CdZnTe crystals (the current material of choice for room-temperature radiation detection).

A disadvantage of this work may be considered to be that the description and illustration of the invention are an example, and the invention is not limited to the exact details shown or described.

Disclosure of the essence of the utility model

The objective of the utility model is to develop an X-ray detector for recording ionizing X-ray radiation in a wide range of energies and fluxes.

The technical result of the utility model is an increase in the detector speed by 1.5-2 times and an increase in the useful signal amplitude by 1.5-3 times due to the use of a layered structure p+/i/n+GaAs and the technology of packaging in the SPPD11-xx housing. This, in turn, made it possible to create highly sensitive detectors with subnanosecond speed, increase the useful signal amplitude and make a device with a longer service life.

The technical result is achieved due to the fact that the sensitive element from a certain layered structure of wide-bandgap semiconductor material (p+/i/n+GaAs) will be placed in the housing of the SPPD11-xx. In this regard, the subnanosecond speed increases, the amplitude of the useful signal increases and the service life of the device increases.

The problem is solved by the fact that the sensitive element is a p-i-n structure made by the method of gas-phase epitaxy from organometallic compounds at reduced pressure and temperatures, containing a GaAs substrate consisting of:

i-GaAs layer;

n+-GaAs layer;

solid contact Pt/TiN/Ag.

p+-GaAs layer;

Ti/Pd/Au metallization layer;

polyamide layer.

The crystal structure was formed from several layers: p+-GaAs (0.3 μm), i-GaAs (40 μm), n+-GaAs (500 μm). To create an ohmic contact to the n+-GaAs layer, a continuous Pt/TiN/Ag contact with a total thickness of 0.1 μm was formed on the surface. To form a composite ohmic contact with the p+-GaAs substrate, Ti/Pd/Au metallization with a thickness of 100 nm was used.

The body element was made from copper sheets, from which a circle of 9 mm in diameter was obtained using a wire cutting machine. The lower base was nickel-plated.

Circles for the upper base were made from 9 mm diameter Sitalla material, which were sprayed on the front side with a metal layer using vacuum spraying (Al layer 1 μm thick). The cutting process was carried out on a LaserCut laser cutting machine. The back side was coated with conductive glue and dried in the air for 24 hours.

Wires (4 pieces) were welded to the sample using microwelding. After the microwelding process, a sealant (KLT-30 Compound) was applied to the sample and it was allowed to dry completely.

The method for manufacturing a high-speed detector based on a wide-bandgap semiconductor material for recording pulsed X-ray radiation includes: manufacturing a sensitive element from GaAs, manufacturing a housing for the sensitive element, and placing the housing of the sensitive element with GaAs in the housing of the SPPD11-xx.

The sensitive element made of p+-GaAs (0.3 µm), i-GaAs (40 µm), n+-GaAs (500 µm) has a smaller diameter input window, this sensitive element has a lower operating voltage, it has high response speed and lower dark currents.

Brief description of the drawings

The utility model is illustrated by drawings, where

Fig. 1 shows a schematic image of a GaAs crystal;

Fig. 2 shows a schematic image of the sensing element housing - side view;

Fig. 3 shows a 3D image of the sensitive element housing - side view.

The positions in Fig. 1 indicate:

1 - p+-GaAs layer;

2 - Ti/Pd/Au metallization layer;

3 - polyamide layer;

4 - i-GaAs layer;

5 - n+-GaAs layer;

6 - solid contact Pt/TiN/Ag.

The positions in Fig. 2 indicate:

7 - crystal of p+/i/n+ - GaAs;

8 - sealant;

9 - metal (Cu).

Implementation of a utility model

A high-speed detector based on a wide-bandgap semiconductor material for recording pulsed X-ray radiation is a p-i-n structure produced by the method of gas-phase epitaxy from organometallic compounds at reduced pressure and temperatures. The detector contains a GaAs substrate (Fig. 1) consisting of a p+-GaAs layer - 1, a Ti/Pd/Au metallization layer - 2; a polyamide layer - 3; an i-GaAs layer - 4; an n+-GaAs layer - 5; from a continuous Pt/TiN/Ag contact - 6. The thickness of the p+-GaAs (0.3 µm), i-GaAs (40 µm), n+-GaAs (500 µm) layers, the thickness of the ohmic contact to the n+-GaAs layer on the Pt/TiN/Ag surface is 0.1 µm, the thickness of the composite ohmic contact with the p+-GaAs substrate made of Ti/Pd/Au is 100 nm.

To test the operability, a prototype of a high-speed detector was created based on a wide-band semiconductor material for recording pulsed X-ray radiation, in which the semiconductor detector is a p-i-n structure. The design solution for the manufactured sensitive element corresponds to Fig. 1. Then, a housing for the sensitive element was manufactured, for which a copper sheet was required, from which a circle with a diameter of 9 mm was cut out using a wire cutting unit. The lower base was nickel-plated. A metal layer was sprayed from the front side of a circle of the same diameter (9 mm) using vacuum spraying (aluminum layer 1 μm thick). The cutting process was carried out on a LaserCut laser cutting unit. The back side was covered with conductive glue on silver and dried for a day in the air. Welding of wires (in the amount of 4 pcs.) to the sample was carried out using microwelding, then a sealant was applied.

A high-speed detector based on a wide-bandgap semiconductor material for recording pulsed X-ray radiation operates as follows.

Quanta of pulsed X-ray radiation, getting into the material of the sensitive element, interact with it, which leads to the birth, depending on the energy of the incident quantum: a photoelectron, a Compton electron or an electron-positron pair. Charged particles penetrate into the sensitive area and generate electron-hole pairs in it. The charge carriers (electrons and holes) under the action of the electric field applied to the semiconductor element "dissolve" and move to the electrodes. As a result, an electric pulse appears in the external circuit of the semiconductor detector, which is registered by the charge-sensitive preamplifier and converted into a voltage drop at its output, and then transmitted to the signal processing unit.

The manufactured device was characterized by the following electrical characteristics:

Operating mode - reverse bias at full depletion.

Working voltage 45 V;

Dark current at operating voltage is no more than 0.5 μA.

The duration of the pulse response at the level of 0.5 amplitude, characterizing the response speed, was achieved at about 1.2 ns.

All measurements were carried out at a temperature of 20±2°C.

Thus, the utility model provides for obtaining a detector that can be used in various devices intended for recording and/or measuring ionizing radiation.

Claims (1)

A high-speed detector based on a wide-bandgap semiconductor material for recording pulsed X-ray radiation, which is a p-i-n detector containing a sensitive element with a p+/i/n+ structure, placed in an SPPD11-xx housing, characterized in that the sensitive element is made in the form of a p-i-n structure produced by the method of gas-phase epitaxy from organometallic compounds at reduced pressure and temperatures, containing a GaAs substrate consisting of: an i-GaAs layer; an n+-GaAs layer; a continuous Pt/TiN/Ag contact; a p+-GaAs layer; a Ti/Pd/Au metallization layer; a polyamide layer.