JP2000277789A - Radiation detecting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce junction defect between respective layers by employing a material having a grating constant close to that of a radiation detecting layer in p layer and n layer constituting a radiation detecting element. SOLUTION: A radiation detecting layer 11 is formed of a single crystal Cd0.9Zn0.1Te of 1 mm thick having resistivity of 1010 Ω.cm and the upper surface thereof is doped with p type impurities of form a p type Cd0.9Zn0.1Te layer 13 while the lower surface thereof is doped with n type impurities to form an n type CdSe0.1Te0.9 layer 15. Since the Cd0.9Zn0.1Te forming the radiation detecting layer 11 and the CdSe0.1Te0.9 have grating constants close to each other, junction defect due to difference of grating constant can be reduced by forming the n layer of CdSe0.1Te0.9 and forming the p layer of same material as the radiation detecting layer 11. Consequently, leak current of a radiation detecting element 10 can be suppressed significantly as compared with a radiation detecting element 10 having neither p layer nor n layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detecting element applied to a radiation detector used for medical and industrial X-ray imaging.

[0002]

2. Description of the Related Art FIG. 8 shows a conventional radiation detecting element. This radiation detecting element has a Cd
The radiation detecting layer 11 made of ZnTe has a PIN structure including a ZnTe layer 53 formed by doping a p-type impurity on one side and a CdS layer 55 formed by doping an n-type impurity on the other side.

[0003]

However, in the above radiation detecting element, CdZnTe forming the radiation detecting layer 11 and ZnTe forming the ZnTe layer 53 and CdS forming the CdS layer 55 have different lattice constants. Defects are likely to occur at the junction between the layers, and it has been difficult to significantly suppress leakage current.

Accordingly, an object of the present invention is to provide a radiation detecting element having a configuration that solves the above-mentioned problems.

[0005]

A radiation detecting element according to the present invention comprises a radiation detecting layer comprising Cd, Zn and Te;
C in which one side of the radiation detection layer is doped with a p-type impurity
It is characterized by including a p-layer made of d, Zn and Te, and an n-layer made of Cd, Se and Te doped with an n-type impurity on the other side of the radiation detection layer. By using a material whose lattice constant is close to that of the radiation detection layer for the p-layer and the n-layer as described above, it is possible to reduce junction defects between the respective layers.

In the above radiation detecting element, the n layer may be formed by doping I or Cl. By using I or Cl as the n-type impurity, the radiation detecting element can be easily manufactured.

In the above radiation detecting element, the p layer may be formed by doping N or Na. By using N or Na as the p-type impurity in this way, the radiation detecting element can be easily manufactured.

In the above radiation detecting element, the component ratio of Cd and Zn forming the radiation detecting layer and the p layer is Cd _x Z
In n _1-x Te, 0.01 ≦ x ≦ 0.5, and n
The component ratio of Se and Te forming the layer is CdSe _y Te _1-y
May be characterized in that 0.01 ≦ y ≦ 0.5. With such an atomic ratio, a layer having a PIN structure with a close lattice constant can be easily formed.

In the above radiation detecting element, the n-layer may be grown by a chemical vapor deposition method under a temperature condition of 20 ° C. to 170 ° C. With such a configuration, the quality of the n-layer can be kept high.

In the above radiation detecting element, a Schottky electrode made of Au or Pt may be provided on one side of the radiation detecting layer instead of the p layer. By doing so, the radiation detecting element can be easily manufactured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the photoelectric conversion element according to the present invention will be described with reference to the drawings.

FIG. 1 shows a radiation detecting element 10 of the embodiment.
FIG. The radiation detection layer 11 has a thickness of 1 mm,
Resistance 10^TenΩ · cm single crystal Cd_0.9Zn_0.1Shape from Te
And on one side, the top surface in FIG.
P-type Cd_0.9Zn_0.1Te
A layer 13 is formed, and the other side of the radiation detection layer 11,
That is, the lower surface in FIG. 1 is doped with an n-type impurity.
The n-type CdSe _0.1Te_0.9Layer 15 is formed
You.

FIG. 2 is a diagram showing the lattice constant of each substance. Cd forming the radiation detection layer 11 as shown in FIG.
_It can be seen that _0.9 Zn _0.1 Te and CdSe _0.1 Te _0.9 have similar lattice constants. Therefore, an n-layer is formed using CdSe _0.1 Te _0.9 , and p-layer is formed of the same material as the radiation detection layer 11.
By forming a layer, junction defects due to a difference in lattice constant can be reduced, and leakage current can be greatly suppressed.

FIG. 3 is a diagram showing the amount of leakage current with respect to the applied voltage in comparison between the present embodiment and a conventional product. In FIG. 3, a solid line 21 indicates the amount of leakage current with respect to the applied voltage of the radiation detection element 10 of the present embodiment, and a dotted line 22 indicates the amount of leakage current with respect to the applied voltage of the radiation detection element 10 having neither the p layer nor the n layer. As shown in FIG. 3, it can be seen that the radiation detection element 10 of the present embodiment significantly suppresses the leak current as compared with the radiation detection element 10 having no p layer and n layer.

Next, the operation of the radiation detecting element 10 of this embodiment will be described with reference to the drawings. FIG. 4 is a diagram illustrating an example of the radiation detector 30 in which the radiation detection element 10 of the present embodiment is mounted on a CAN package. Radiation detector 30
As shown in FIG. 4, a ceramic substrate 41 is arranged on the bottom surface of a package 43 having a radiation incident window 45 on the upper part, and the radiation detecting element 10 having electrodes on both sides is arranged on the upper surface of the ceramic substrate 41. ing. The Al electrode 19 provided on the ceramic substrate 41 side of the radiation detecting element 10 is connected to the + potential lead pin 39 by an Au wire 47, and the Au electrode 17 provided on the side opposite to the ceramic substrate 41 of the radiation detecting element 10 is It is connected to the negative potential lead pin 37 by an Au wire 47.

The radiation detector 30 applies a high voltage between the positive potential lead pin 39 and the negative potential lead pin 37, and the electrons excited by the radiation incident from the radiation incident window 45 flow between the two lead pins. It reads the signal change. The reading accuracy can be improved by reducing the leak current by using the radiation detection element 10 of the present embodiment.

Although the embodiments of the radiation detecting element according to the present invention have been described in detail above, the present invention is not limited to the above embodiments. For example, p-type Cd
Instead of the _0.9 Zn _0.1 Te layer, A
A Schottky electrode made of u or Pt may be provided. By doing so, the radiation detecting element can be easily manufactured.

Next, the radiation detecting element 10 of the above-described embodiment will be described.
A method of manufacturing the device will be described. FIG. 5 shows a hydrogen plasma MO
FIG. 6 is a view illustrating a CVD apparatus, FIG. 6 is a view illustrating a laser irradiation chamber, and FIG. 7 is a view illustrating a laser annealing apparatus, which are used in a manufacturing process of the radiation detection element 10 according to the present embodiment.

First, the surface is etched by a thickness of 1 m.
Hydrogen radical excited MOCV using plasma on a single crystal Cd _0.9 Zn _0.1 Te substrate having a resistance of 10 mΩ and a resistance of 10 ¹⁰ Ω · cm
A CdSe _0.1 Te _0.9 layer is grown by the D method. Specifically, first, the single crystal Cd _0.9 Zn _0.1 Te substrate 11 is set on the susceptor 117 of the MOCVD apparatus 100 shown in FIG. 5, DMCd and DETe are supplied from the gas introduction pipe 101, and SeH ₂ , n is supplied from the gas introduction pipe 103. -BtI is introduced into the MOCVD apparatus 100 as a material gas. In addition, each gas introduction rate is DMCd = 24 μmol / min,
DETe = 12 μmol / min, SeH ₂ = 6 μmo
1 / min, n-BtI = 1 μmol / min, M
The exhaust speed of the gas from the exhaust pipe 105 is adjusted so that the gas pressure in the OCVD apparatus 100 becomes 0.2 Torr.

Next, hydrogen gas is introduced from the nozzle 113 connected to the MOCVD apparatus 100 at a flow rate of 10 sccm. The introduced hydrogen gas is plasma-excited by the high-frequency coil 115 to become hydrogen radicals, and Cd _0.9 Zn _0.1
It reaches the surface of the Te substrate 11, where it reacts with the material gas. Cd _0.9 Zn _0.1
CdSe doped with n-type impurities on the surface of the Te substrate 11
_An n layer of _0.1 Te _0.9 is formed. At this time, Cd
_In order to control the film thickness of the n-layer formed on the surface of the _0.9 Zn _0.1 Te substrate 11, light is emitted from the laser 107 to emit Cd.
_The light pressure reflected on the _0.9 Zn _0.1 Te substrate 11 is received by the photodiode 109 to measure the film pressure of the formed n-layer. Cd _0.9 Zn _0.1 Te during this reaction
The temperature of the substrate 11 is 20 ° C. to 170 by the heater 121.
Kept at ° C. This is due to the Cd
_This is because the characteristics of the _0.9 Zn _0.1 Te substrate 11 deteriorate, resulting in an increase in leakage current.

Next, p-type C is formed by laser doping.
forming the d _0.9 Zn _0.1 Te layer. Specifically, the above CdS
On the surface opposite to the surface on which e _0.1 Te _0.9 is deposited, 30 nm of Na ₂ Te is deposited by a vacuum deposition method. Then, the substrate 1
1 is a window 133 for introducing light into the upper part as shown in FIG.
1 of laser irradiation chamber 130 having
31 As Na ₂ Te during laser irradiation while moving does not evaporate on, place the quartz glass on the face with a deposit of Na ₂ Te, the laser irradiation chamber 130 kept 3 atm in a nitrogen atmosphere.

Next, a KrF excimer laser 143 is used to perform laser annealing on the Na ₂ Te vapor-deposited surface. As shown in FIG. 7, light emitted from the KrF excimer laser 143 is introduced into the laser irradiation chamber 130 via the mirror 145 and the lens 147. The control of the excimer laser 143 is performed by the controller 141. The surface of the Cd _0.9 Zn _0.1 Te substrate is doped with Na by laser annealing using the excimer laser 143 to form a p-type Cd _0.9 Zn _0.1 Te layer, and the radiation detecting element 10 of the above embodiment is completed. The KrF excimer laser 143 used here
Emits laser light with λ = 248 nm and pulse width = 20 ns.

[0023]

According to the present invention, the radiation detecting layer C
CdS having a lattice constant almost the same as that of dZnTe
By using eTe and CdZnTe for the n-layer and the p-layer, respectively, it is possible to realize a radiation detecting element having a configuration in which defects at the junction between the layers are reduced, and the leak current is greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a radiation detection element according to an embodiment.

FIG. 2 is a diagram showing the lattice constant of each substance.

FIG. 3 is a diagram illustrating a leak current amount with respect to an applied voltage.

FIG. 4 is a diagram illustrating a radiation detector on which the radiation detection element according to the embodiment is mounted.

FIG. 5 is a diagram showing a hydrogen plasma MOCVD apparatus.

FIG. 6 is a view showing a laser irradiation chamber.

FIG. 7 is a view showing a laser annealing apparatus.

FIG. 8 is a diagram showing a conventional radiation detection element.

[Explanation of symbols]

 10 radiation detecting element, 11 radiation detecting layer,
13 ... p-type Cd _0.9Zn_0.1Te layer, 15 ... n
Type CdSe_0.1Te_0.9Layer, 17 ... Au electrode, 19
... Al electrode, 21 ... Radiation detection element of this embodiment
Leak current amount with respect to the applied voltage of the element, 22... P layer,
Leakage with respect to applied voltage of a radiation detecting element having no n-layer
Current amount, 30 ... Radiation detector, 37 ...- potential
Lead pin, 39 ... + potential lead pin, 41 ...
Ceramic substrate, 43 ... package, 45 ... release
Ray incidence window, 47 ... Au wire, 53 ... ZnT
e layer, 55 ... CdS layer, 100 ... MOCVD equipment
, 101, 103 ... gas introduction pipe, 105 ... gas
Discharge pipe, 107 laser, 109 photo
Diode, 113 ... nozzle, 115 ... high frequency
Coil, 117: susceptor, 121: heater
ー 、 130 ・ ・ ・ Laser irradiation chamber 、 131 ・
..Susceptors, 133, windows, 141, control
143, KrF excimer laser, 145
... Mirror, 147 ... Lens.

Claims (6)

[Claims] 1. A radiation detection layer made of Cd, Zn and Te; a p-layer made of Cd, Zn and Te doped with a p-type impurity on one side of the radiation detection layer; and the other side of the radiation detection layer A Cd, Se and Te n-layer doped with an n-type impurity. 2. The radiation detecting element according to claim 1, wherein the n-layer is formed by doping I or Cl. 3. The radiation detecting element according to claim 1, wherein the p layer is formed by doping N or Na. 4. The composition ratio of Cd and Zn forming the radiation detection layer and the p layer is 0.01 ≦ x ≦ 0.5 in Cd _x Zn _1-x Te, and forms the n layer. The component ratio of Se and Te is CdSe _y
2. The method according to claim 1, wherein in Te _1-y , 0.01 ≦ y ≦ 0.5.
The radiation detection element according to any one of claims 1 to 3. 5. The method according to claim 5, wherein the n-layer is formed by chemical vapor deposition.
The radiation detecting element according to any one of claims 1 to 4, wherein the radiation detecting element is grown under a temperature condition of 0 ° C to 170 ° C. 6. The method according to claim 1, wherein a Schottky electrode made of Au or Pt is provided on one side of the radiation detection layer instead of the p layer. Radiation detection element.