RU2307425C1 - Solid-state ionizing radiation detector - Google Patents

Abstract

FIELD: ionizing radiation detectors.

SUBSTANCE: proposed ionizing radiation detector has GaAs substrate with contacts, its boundary semi-insulated layer, and ohmic contact. In addition it has Ga_{1 - x}Al_xAs insulating layer having common boundary with semi-insulating GaAs layer, non-doped GsAs layer having common boundary with Ga_{1 - x}Al_xAs insulating layer, GsAs doping layer of n polarity of conductivity having common boundary with non-doped GaAs layer that carries additional ohmic and barrier contacts. All these layers and above-mentioned ohmic contact form field-effect transistor incorporating p region formed in doped and non-doped GaAs layers and in GaAlAd insulating layer, as well as high-resistance region disposed on periphery of mentioned transistor.

EFFECT: enhanced threshold sensitivity and resolving power, reduced noise level, ability of detecting weak ionizing streams.

1 cl, 1 dwg

Description

The invention relates to solid-state detectors of ionizing radiation.

Solid-state detectors of ionizing radiation are the elemental base of the diagnostic systems of nuclear plants, exploration, environmental monitoring of the environment and medical equipment.

Known detectors of ionizing radiation, the principle of which is based on the ionization of the working gas and the proportional conversion of the energy of a quantum (particle) into the current of the mentioned ions [1].

The main advantage of such detectors is their high resistance to radiation dose rates. Their disadvantages include poor spatial resolution, which prevents their use in beam positioning systems and recognition of flat images.

Also known is a silicon solid-state detector of a barrier type [2]. It allows one to significantly increase the spatial resolution of the detector, which makes it possible to actively use such detectors for tasks related to beam positioning, medical diagnostics, and for flaw detection.

However, Si detectors also have a number of significant drawbacks. So, in solid-state silicon detectors, the regions of the conversion of quantum energy (particles) into nonequilibrium electron-hole pairs and subsequent reading of carriers in the form of current into an external circuit are spatially aligned, which leads to the destruction of an informative charge when it is read into an external circuit. In addition, the disadvantages of silicon solid state detectors are also low resistance to radiation dose loads. The last of the disadvantages can be overcome by using detectors based on alternative solid state materials, for example, resistive or barrier detectors based on gallium arsenide [3].

As a prototype of the present invention, a resistive or barrier detector based on high resistance gallium arsenide is proposed [3]. The prototype detector is a gallium arsenide substrate with a contact and a semi-insulating (functional receiving) layer of gallium arsenide with an ohmic or barrier contact adjacent to it. In the prototype detector, the areas of conversion of quantum energy (particles) into nonequilibrium electron-hole pairs and subsequent reading of carriers in the form of current into an external circuit are spatially aligned. Because of this, in this design [3], as well as in the design of the analogue [2], reading the charge into an external circuit leads to a loss of the information signal, and the recorded threshold values of ionizing radiation, energy resolution, and energy noise are determined not only by background (“dark” ) by currents, but also by thermal and generation-recombination noises, extremely significant when reading currents flowing in high-resistance materials compensated by deep energy centers.

An object of the present invention is to provide a detector with a high threshold sensitivity, low noise and high energy resolution. This goal is achieved by means of a design that allows you to accumulate a charge and read it non-destructively in the accumulation process.

To this end, a Ga _1-x Al _x As insulating layer having a common boundary with said semi-insulating gallium arsenide-gallium layer, an undoped gallium arsenide layer, is introduced into a solid-state gallium arsenide-gallium detector prototype containing a substrate with a contact to it and a semi-insulating gallium arsenide layer with an ohmic contact adjacent to it. having a common boundary with the insulating layer of Ga _1-x Al _x as, gallium arsenide doped layer n-type conductivity, having a common border with the undoped GaAs layer and said ohmic contact and supple Yelnia barrier and ohmic contacts disposed on the doped GaAs layer so as to form with it a field effect transistor; In addition, in the doped layer of gallium arsenide of n-type conductivity, undoped GaAs and the insulating layer of gallium arsenide - aluminum arsenide, up to the semi-insulating gallium arsenide layer, a local region of p-type conductivity is made.

Achieving a positive effect (the ability to save and accumulate an information charge and non-destructively read information about it) is ensured by the fact that the region in which the energy of ionizing radiation is converted into nonequilibrium electron-hole pairs, the subsequent removal of holes and the accumulation of an nonequilibrium electron charge on traps of the semi-insulating layer, separated by a single-crystal insulating layer of a solid solution of gallium arsenide - aluminum arsenide from the reading area and formation of a charge which is read as a current flowing in the channel of said field effect transistor above.

The proposed design of the device allows one to significantly increase the threshold sensitivity, since it eliminates the contributions of the thermal and shot components of noise inherent to resistive detectors based on high-resistance compensated material, while reading information about the charge through a substantially less noisy channel in the epitaxial layer.

The proposed design allows the detection of plane images in flows of particles or ionizing radiation, implements modes of accumulation, reading and destruction of the information charge on the traps of a semi-insulating GaAs layer.

In the design presented on the drawing, the inventive detector contains:

1 - gallium arsenide substrate with contact to it;

2 - semi-insulating GaAs layer having a common border with the substrate;

3 - insulating single-crystal GaAlAs layer having a common border with a semi-insulating layer 2;

4 - undoped GaAs layer having a common border with the insulating layer 3;

5 - doped GaAs layer of n-type conductivity, having a common border with undoped layer 4;

6, 7 - two ohmic contacts located on the doped layer 5;

8 - barrier contact located on the doped layer 5;

9 - barrier contact in the form of a region of p-type conductivity;

10 - high-resistance region located on the periphery of the transistor.

Layer 2 of this design is functionally a transceiving layer, i.e. the region in which the processes of energy conversion of radiation quanta or high-energy particles into electron-hole pairs occur. The isolating single-crystal GaAlAs layer 3 [5, 6] is designed for galvanic isolation of layer 2 with epitaxial GaAs layers 4 (undoped GaAs layer) and 5 (n-type GaAs layer). GaAs doped layer 5 with formed ohmic (6 and 7) and barrier (8) contacts forms a GaAs field effect transistor, which functionally acts as an information reader. The barrier contact 9 in the form of a p-type conduction region is designed to destroy (erase) the informative charge, as well as to evacuate nonequilibrium holes in the process of registration and accumulation of electron charge. The high-resistance region 10, made in layers 4 and 5 by means of boron implantation (for example, with energies of 40 ... 60 keV and a dose of 30 microcoulomb), plays the role of planar isolation of the receiving region of the sensor crystal (the area including the transistor) from the passive part of the crystal.

The detector is as follows. High-energy particles or gamma quanta interact with the ions of the lattice of the volume of layer 2 according to one of the known mechanisms, converting the energy of ionizing radiation into nonequilibrium electrons and holes [7], followed by localization of nonequilibrium electrons in the traps of layer 2. In this case, a p ⁺ / n transition is applied reverse bias voltage (minus p ⁺ regions relative to layer 2), so that nonequilibrium holes are evacuated from layer 2. An excess electron charge localized on the traps of layer 2, the magnitude of which is proportional to the flux ionizing radiation, creates an SCR in layer 5 of the channel of the field effect transistor, reducing the current flowing through the channel of the transistor. In this case, due to the galvanic isolation of layers 4 and 5 and the receiving layer 2, the possibility of spontaneous recharging of the traps of the boundary region due to the current of the “hot” carriers of the transistor channel is excluded, which allows reading information about the localized charge (and hence the ionizing radiation flux) without distorting the information charge. The discharge of the layer (traps of layer 2) is carried out by applying to the p ⁺ electrode an impulse (non-stationary) of the reverse bias (minus) of the p ⁺ / n junction that exceeds the threshold value.

The thickness of the receiving layer 2 depends on the type and energy of the detected radiation. So, when detecting α particles, its thickness is determined by the radiation length, and for energies of ~ 5 MeV it will be ~ 30 μm. When detecting X-ray quanta (1 ... 10 keV), the thickness of the semi-insulating GaAs layer is determined by the cross section of the quantum - layer 2 interaction process, which will be ~ 100 ... 300 μm for detectors based on GaAs materials.

The separation layer 3 of Ga _1-x Al _x As has an electric strength of ~ 10 ⁶ V / cm, so that taking into account the expected potential from localized traps, its thickness can be in the range 0.15 ... 0.30 μm.

The functional purpose of unalloyed layer 4 is a technological buffer layer; it is designed to relieve elastic stresses of the GaAlAs / GaAs interface, and its thickness can vary between 0.1 ... 0.3 microns. The molar fraction of aluminum arsenide in the solid solution of this layer is in the range 0.15 ... 0.35 [5, 6].

The thickness of the doped GaAs layer 5 varies together with changes in the concentration of the dopant in the ranges 0.2 ... 0.6 μm and 2.10 ¹⁷ cm ^-3 ... 2.10 ¹⁶ cm ^-3, respectively.

The size of the local region associated with diffuse image blurring, due to the small capture time (~ 10 ^-11 s) and the insignificance of the concentration gradient of nonequilibrium carriers (for energies of detected α particles of ~ 5 MeV, does not exceed 10 ⁶ pc / μm) does not exceed 1 ... 2 μm, which makes the detector relevant for recording flat images in ionizing radiation streams. Given the spatial diversity of the read element and the charge storage area, the resolution of the image in the plane of the plate will depend on the thickness of the receiving layer 2, and therefore will vary depending on the type of radiation detected and its energy characteristics.

Information sources

1. Price V. // Registration of nuclear radiation. Ed. "Publishing house of foreign literature", Moscow, 1960.

2. Bellini J., Foa A., George M. // Uspekhi Fizicheskikh Nauk. 1984, vol. 142. S.476-503.

3. J.C. Bourgoin, N. de Angelis, K.Smith, R. Bates, C. Whitehill, A. Meikle. // Nuclear Instruments and Methods in Physics Research A 458 (2001) 344-347 - prototype.

4. D.S. McGregor, S. M. Vernor, H. K. Gersch, S. M. Markham, S. J. Wojtczuk, D. K. Wehe. // IEEE Transactions on nuclear science, v.47, n.4, p.1365-1370.

5. Ilyichev EA, Masloboev Yu.P., Poltoratsky EA, Rodionov AV, Slepnev Yu.V. // Auth. Testimonial. No. 1119523, priority dated March 28, 83, issued June 13, 84.

6. Afanasyev A.A., Ilyichev E.A., Poltoratsky E.A., Slepnev Yu.V., Rodionov A.V. // FTP, 1985, v.20, v.9, p. 1565-1571.

7. V. B. B. Berestetskiy, E. M. Livshits, L. P. Pitaevsky. // Relativistic quantum theory, part 1. Ed. "Science", Moscow, 1968.

Claims (1)

A solid-state ionizing radiation detector containing a gallium arsenide substrate with a contact, a semi-insulating gallium arsenide layer adjacent to it and an ohmic contact, characterized in that an insulating Ga _1-x Al _x As layer is introduced, having a common boundary with a semi-insulating gallium arsenide, an undoped gallium arsenide layer, a common boundary with the insulating layer of Ga _1-x Al _x As, gallium arsenide doped layer n-type conductivity, having a common border with the undoped GaAs layer formed on it with additional ohmic and ba ernym contacts, which together with the above ohmic contact to form a field effect transistor, the region of p-type conductivity formed in the doped and undoped GaAs layers of GaAlAs and the insulating layer and the high resistance region, located around the periphery of said transistor.