X-ray semiconductor detector and method for manufacturing same

Abstract

This X-ray semiconductor detector (2) comprises an i-type nitride semiconductor substrate (10), a p-type semiconductor layer (16), a n-type semiconductor layer (17), a first electrode (21), and a second electrode (22). An i-type nitride semiconductor substrate (10) has a first main surface (11) and a second main surface (12). The p-type semiconductor layer (16) is formed on the first main surface (11). The n-type semiconductor layer (17) is formed on the second main surface (12). The first electrode (21) is formed on the p-type semiconductor layer (16). The second electrode (22) is formed on the n-type semiconductor layer (17). The first main surface (11) and the second main surface (12) are non-polar surfaces of nitride semiconductor crystals constituting the i-type nitride semiconductor substrate (10) or surfaces inclined by an off-angle within 5° from the non-polar surfaces.

Description

X-ray semiconductor detector and method for manufacturing the same

[0001] This disclosure relates to an X-ray semiconductor detector and a method for manufacturing the same.

[0002] Japanese Patent Publication No. 2002-503389 (Patent Document 1) discloses an X-ray detection device. This X-ray detection device comprises an i-type semiconductor layer having a first surface portion and a second surface portion, a p-type semiconductor region on the first surface portion, an n-type semiconductor region on the second surface portion, a first electrical contact on the p-type semiconductor region, and a second electrical contact on the n-type semiconductor region. The i-type semiconductor layer is made of In ｘ Ga １－ｘ It is formed by N, and x is between 0 and 40%.

[0003] Special Publication No. 2002-503389

[0004] The object of this disclosure is to provide an X-ray semiconductor detector having improved detection accuracy for X-rays.

[0005] The X-ray semiconductor detector of this disclosure comprises an i-type nitride semiconductor substrate, a p-type semiconductor layer, an n-type semiconductor layer, a first electrode, and a second electrode. The i-type nitride semiconductor substrate has a first main surface and a second main surface opposite to the first main surface. The p-type semiconductor layer is formed on the first main surface. The n-type semiconductor layer is formed on the second main surface. The first electrode is formed on the p-type semiconductor layer. The second electrode is formed on the n-type semiconductor layer. The first and second main surfaces are nonpolar surfaces of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate, or surfaces tilted by an off-angle of 5° or less from the nonpolar surface.

[0006] The present disclosure provides a method for manufacturing an X-ray semiconductor detector, comprising preparing an i-type nitride semiconductor substrate having a first main surface and a second main surface opposite to the first main surface. The first and second main surfaces are nonpolar surfaces of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate, or surfaces inclined by an off-angle of 5° or less from the nonpolar surface. The present disclosure provides a method for manufacturing an X-ray semiconductor detector, comprising forming a p-type semiconductor layer on the first main surface, forming an n-type semiconductor layer on the second main surface, forming a first electrode on the p-type semiconductor layer, and forming a second electrode on the n-type semiconductor layer.

[0007] The X-ray semiconductor detector and method for manufacturing the same described herein can provide an X-ray semiconductor detector having improved detection accuracy for X-rays.

[0008] Figure 1 is a schematic plan view of the X-ray semiconductor detection apparatus according to the embodiment. Figure 2 is a schematic cross-sectional view of the X-ray semiconductor detection apparatus according to the embodiment. Figure 3 is a schematic enlarged cross-sectional view of the X-ray semiconductor detector according to the embodiment. Figure 4 is a flowchart showing the manufacturing method of the X-ray semiconductor detector according to the embodiment. Figure 5 is a flowchart showing an example of the process for preparing an i-type nitride semiconductor substrate. Figure 6 is a schematic perspective view showing the process for cutting a nitride semiconductor ingot. Figure 7 is a schematic diagram showing the plane orientation of a nitride semiconductor crystal.

[0009] Embodiments of the present disclosure will be described below. The same components will be given the same reference numerals, and their descriptions will not be repeated.

[0010] The X-ray semiconductor detection device 1 of this embodiment will be described with reference to Figures 1 and 2. The X-ray semiconductor detection device 1 is mounted on, for example, an X-ray diagnostic device such as a mammography device, an X-ray computed tomography device, or a satellite.

[0011] The X-ray semiconductor detection device 1 comprises a plurality of X-ray semiconductor detectors 2 and a circuit board 3. The plurality of X-ray semiconductor detectors 2 are arranged two-dimensionally on the circuit board 3. The X-ray semiconductor detection device 1 is an X-ray flat panel detector (FPD). The circuit board 3 includes a detection circuit 4. The detection circuit 4 is electrically connected, for example, to the second electrode 22 (see Figure 2) of each of the plurality of X-ray semiconductor detectors 2. The detection circuit 4 detects the current pulses of each of the pixels 2a, 2b, and 2c of the X-ray semiconductor detectors 2 when X-rays 30 are incident on the X-ray semiconductor detectors 2. The detection circuit 4 is, for example, a semiconductor integrated circuit.

[0012] Referring to Figure 3, the X-ray semiconductor detector 2 of this embodiment will be described. It comprises an i-type nitride semiconductor substrate 10, a p-type semiconductor layer 16, an n-type semiconductor layer 17, a first electrode 21, and a second electrode 22. The X-ray semiconductor detector 2 may further include a voltage source 25.

[0013] The i-type nitride semiconductor substrate 10 is, for example, an i-type gallium nitride (GaN) substrate. The i-type nitride semiconductor substrate 10 has, for example, an electrical resistivity of 1×10 ６ Ω·cm or more. The i-type nitride semiconductor substrate 10 is a high-purity nitride semiconductor substrate. For example, the concentration of silicon (Si) as an impurity contained in the i-type nitride semiconductor substrate 10 is 1×10 １５ atoms / cm ３ or less. The concentration of boron (B) as an impurity contained in the i-type nitride semiconductor substrate 10 is 1×10 １５ atoms / cm ３ or less. The concentration of oxygen (O) as an impurity contained in the i-type nitride semiconductor substrate 10 is 1×10 １５ [[ID=1'2]] atoms / cm ３ or less. The concentration of iron (Fe) as an impurity contained in the i-type nitride semiconductor substrate 10 is 1×10 １５ atoms / cm ３ or less.

[0014] The i-type nitride semiconductor substrate 10 has a first main surface 11, a second main surface 12 opposite to the first main surface 11, a side surface 13, and a side surface 14 opposite to the side surface 13.

[0015] The first main surface 11 and the second main surface 12 are m-planes of a nitride semiconductor crystal (wurtzite-type crystal) constituting the i-type nitride semiconductor substrate 10. That is, the i-type nitride semiconductor substrate 10 is an m-plane substrate. The fact that the first main surface 11 and the second main surface 12 are m-planes of the nitride semiconductor crystal means that the first main surface 11 is the +m-plane of the nitride semiconductor crystal and the second main surface 12 is the -m-plane of the nitride semiconductor crystal, or the first main surface 11 is the -m-plane of the nitride semiconductor crystal and the second main surface 12 is the +m-plane of the nitride semiconductor crystal.

[0016] The first main surface 11 and the second main surface 12 may be surfaces tilted by an off-angle of 5° or less from the m-plane of the nitride semiconductor crystal (wurtzite crystal) constituting the i-type nitride semiconductor substrate 10. That is, the i-type nitride semiconductor substrate 10 may be an m-plane off-surface substrate. The fact that the first main surface 11 and the second main surface 12 are surfaces tilted by an off-angle of 5° or less from the m-plane of the nitride semiconductor crystal means that the first main surface 11 is a surface tilted by an off-angle of 5° or less from the +m-plane of the nitride semiconductor crystal and the second main surface 12 is a surface tilted by an off-angle of 5° or less from the -m-plane of the nitride semiconductor crystal, or the first main surface 11 is a surface tilted by an off-angle of 5° or less from the -m-plane of the nitride semiconductor crystal and the second main surface 12 is a surface tilted by an off-angle of 5° or less from the +m-plane of the nitride semiconductor crystal.

[0017] Sides 13 and 14 are connected to the first main surface 11 and the second main surface 12, respectively. Sides 13 and 14 are, for example, the c-planes of the nitride semiconductor crystal (wurtzite crystal) that constitutes the i-type nitride semiconductor substrate 10. The fact that side surfaces 13 and 14 are c-planes of the nitride semiconductor crystal means that side surface 13 is the +c-plane of the nitride semiconductor crystal and side surface 14 is the -c-plane of the nitride semiconductor crystal, or that side surface 13 is the -c-plane of the nitride semiconductor crystal and side surface 14 is the +c-plane of the nitride semiconductor crystal.

[0018] The i-type nitride semiconductor substrate 10 contains a plurality of through-dislocations 15. The plurality of through-dislocations 15 mainly extend along the c-axis direction of the nitride semiconductor crystal (wurtzite-type crystal) constituting the i-type nitride semiconductor substrate 10. For example, the plurality of through-dislocations 15 mainly extend along the direction in which the side surface 13 and the side surface 14 face each other.

[0019] The p-type semiconductor layer 16 is formed on the first main surface 11. The p-type semiconductor layer 16 is, for example, a nitride semiconductor layer doped with a p-type dopant. The p-type semiconductor layer 16 is, for example, a p-type gallium nitride layer. The p-type dopant is, for example, magnesium (Mg).

[0020] The n-type semiconductor layer 17 is formed on the second main surface 12. The n-type semiconductor layer 17 is, for example, a nitride semiconductor layer doped with an n-type dopant. The n-type semiconductor layer 17 is, for example, an n-type gallium nitride layer. The n-type dopant is, for example, silicon (Si). The p-type semiconductor layer 16, the i-type nitride semiconductor substrate 10, and the n-type semiconductor layer 17 form a PIN junction.

[0021] The first electrode 21 is formed on a p-type semiconductor layer 16 and is a p-type electrode. The first electrode 21 is, for example, a Ni / Au electrode. The X-ray semiconductor detector 2 includes a plurality of pixels 2a, 2b, 2c. The first electrode 21 is formed, for example, spanning across the plurality of pixels 2a, 2b, 2c.

[0022] The second electrode 22 is formed on an n-type semiconductor layer 17 and is an n-type electrode. The second electrode 22 is, for example, a Ti / Al / Ti / Au electrode. The second electrode 22 is formed by dividing it into, for example, one of the multiple pixels 2a, 2b, and 2c of the X-ray semiconductor detector 2.

[0023] The voltage source 25 applies a reverse bias voltage to the PIN junction formed by the p-type semiconductor layer 16, the i-type nitride semiconductor substrate 10, and the n-type semiconductor layer 17. Specifically, the voltage applied to the first electrode 21 is lower than the voltage applied to the second electrode 22.

[0024] Referring to Figures 4 to 6, an example of a method for manufacturing the X-ray semiconductor detector 2 of this embodiment will be described.

[0025] Referring to Figure 4, an i-type nitride semiconductor substrate 10 having a first main surface 11 and a second main surface 12 is prepared (step S1). The first main surface 11 and the second main surface 12 are the m-plane or a plane inclined by an off-angle of 5° or less from the m-plane of the nitride semiconductor crystal (wurtzite-type crystal) constituting the i-type nitride semiconductor substrate 10. Referring to Figures 5 and 6, an example of step S1 will be described.

[0026] Referring to Figure 5, a growth substrate (not shown) is prepared (step S11). The growth substrate includes, for example, a sapphire substrate (not shown) and a seed layer (not shown) formed on the sapphire substrate. The seed layer is, for example, a gallium nitride (GaN) thin layer.

[0027] Referring to Figures 5 and 6, a nitride semiconductor ingot 33 is grown on a growth substrate (more specifically, a seed layer) by hydride vapor phase growth (HVPE) (step S12). The growth substrate is then removed. Thus, the nitride semiconductor ingot 33 shown in Figure 6 is obtained. The nitride semiconductor ingot 33 is, for example, a gallium nitride (GaN) ingot. The nitride semiconductor ingot 33 has a main surface 34 and a main surface 35 opposite to the main surface 34. The main surfaces 34 and 35 face each other in the thickness direction of the nitride semiconductor ingot 33.

[0028] The main surfaces 34 and 35 are the c-planes of the nitride semiconductor crystal (wurtzite-type crystal) constituting the nitride semiconductor ingot 33. The main surfaces 34 and 35 are the crystal growth surfaces in step S12. In step S12, the nitride semiconductor ingot 33 grows along the c-axis of the nitride semiconductor crystal constituting the nitride semiconductor ingot 33. Compared to the case where the nitride semiconductor crystal is grown along the m-axis of the nitride semiconductor crystal, the thickness of the nitride semiconductor ingot 33 increases. The thickness of the nitride semiconductor ingot 33 is, for example, 1.0 mm or more. The thickness of the nitride semiconductor ingot 33 may be 2.0 mm or more, or 3.0 mm or more. The thickness of the nitride semiconductor ingot 33 is the distance between the main surface 34 and the main surface 35.

[0029] Referring to Figures 5 and 6, the nitride semiconductor ingot 33 is cut along the m-plane of the nitride semiconductor crystal (wurtzite-type crystal) constituting the nitride semiconductor ingot 33, or along a plane tilted by an off-angle of 5° or less from the m-plane (step S13). In this way, a nitride semiconductor piece 36 is obtained.

[0030] The nitride semiconductor piece 36 is subjected to processing such as splitting and polishing to be shaped into a form suitable for incorporation into the X-ray semiconductor detection device 1 (step S14). In this way, the i-type nitride semiconductor substrate 10 is obtained. The first main surface 11 and the second main surface 12 of the i-type nitride semiconductor substrate 10 are the m-plane of the nitride semiconductor crystal (wurtzite-type crystal) constituting the i-type nitride semiconductor substrate 10, or surfaces inclined by an off-angle of 5° or less from the m-plane.

[0031] Referring to Figure 4, a p-type semiconductor layer 16 is formed on the first main surface 11 of the i-type nitride semiconductor substrate 10 by metal-organic chemical vapor deposition (MOCVD) (step S2). An n-type semiconductor layer 17 is formed on the second main surface 12 by MOCVD (step S3). Steps S2 and S3 may be performed in any order.

[0032] Referring to Figure 4, a first electrode 21 is formed on the p-type semiconductor layer 16 by vapor deposition (step S4). A second electrode 22 is formed on the n-type semiconductor layer 17 by vapor deposition (step S5). Steps S4 and S5 may be performed in any order. In this way, an X-ray semiconductor detector 2 is obtained.

[0033] The operation of the X-ray semiconductor detector 2 of this embodiment will be explained in comparison with the X-ray semiconductor detector of the comparative example.

[0034] The X-ray semiconductor detector of the comparative example is configured similarly to the X-ray semiconductor detector 2 of this embodiment, but differs from the X-ray semiconductor detector 2 of this embodiment in that the first main surface 11 and the second main surface 12 are c-planes of the nitride semiconductor crystal (wurtzite crystal) constituting the i-type nitride semiconductor substrate 10. That is, in the comparative example, the i-type nitride semiconductor substrate 10 is a c-plane substrate. Multiple threading dislocations 15 extend along the c-axis of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate 10, extending from the first main surface 11 to the second main surface 12.

[0035] When the X-ray semiconductor detector 2 is not irradiated with X-rays 30, a dark current is generated in the X-ray semiconductor detector 2. The dark current flows through the surface of multiple penetration dislocations 15. In the comparative example, since the multiple penetration dislocations 15 extend from the first main surface 11 to the second main surface 12, a large amount of dark current flows between the first electrode 21 and the second electrode 22. Therefore, the detection accuracy of the X-ray semiconductor detector in the comparative example for X-rays 30 is low.

[0036] In contrast, in the X-ray semiconductor detector 2 of this embodiment, the first main surface 11 and the second main surface 12 are the m-plane or a surface tilted by an off-angle of 5° or less from the m-plane of the nitride semiconductor crystal (wurtzite crystal) constituting the i-type nitride semiconductor substrate 10. Since the multiple threading dislocations 15 extend along the c-axis of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate 10, the multiple threading dislocations 15 extending from the first main surface 11 to the second main surface 12 are significantly reduced or eliminated. The dark current flowing between the first electrode 21 and the second electrode 22 is reduced. Therefore, the detection accuracy of the X-ray semiconductor detector 2 of this embodiment for X-rays 30 is improved.

[0037] The first main surface 11 and the second main surface 12 may be nonpolar surfaces of the nitride semiconductor crystal. The nonpolar surfaces of the nitride semiconductor crystal are surfaces perpendicular to the c-plane of the nitride semiconductor crystal, and for example, as shown in Figure 7, include the a-plane of the nitride semiconductor crystal and the surfaces between the a-plane and the m-plane of the nitride semiconductor crystal, in addition to the m-plane of the nitride semiconductor crystal. In step S13, the nitride semiconductor ingot 33 may be cut along the nonpolar surface of the nitride semiconductor crystal (wurtzite-type crystal) constituting the nitride semiconductor ingot 33 or along a surface inclined by an off-angle of 5° or less from the nonpolar surface.

[0038] The effects of the X-ray semiconductor detector 2 of this embodiment and its manufacturing method will be explained. The X-ray semiconductor detector 2 of this embodiment comprises an i-type nitride semiconductor substrate 10, a p-type semiconductor layer 16, an n-type semiconductor layer 17, a first electrode 21, and a second electrode 22. The i-type nitride semiconductor substrate 10 has a first main surface 11 and a second main surface 12 opposite to the first main surface 11. The p-type semiconductor layer 16 is formed on the first main surface 11. The n-type semiconductor layer 17 is formed on the second main surface 12. The first electrode 21 is formed on the p-type semiconductor layer 16. The second electrode 22 is formed on the n-type semiconductor layer 17. The first main surface 11 and the second main surface 12 are nonpolar surfaces of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate 10, or surfaces tilted by an off-angle of 5° or less from the nonpolar surface.

[0039] Therefore, the plurality of through dislocations 15 extending from the first main surface 11 to the second main surface 12 are significantly reduced or eliminated. The dark current flowing between the first electrode 21 and the second electrode 22 is reduced. The X-ray semiconductor detector 2 has improved detection accuracy with respect to the X-rays 30.

[0040] In the semiconductor X-ray detector 2 of the present embodiment, the non-polar plane of the nitride semiconductor crystal is the m-plane of the nitride semiconductor crystal.

[0041] Therefore, the plurality of through dislocations 15 extending from the first main surface 11 to the second main surface 12 are significantly reduced or eliminated. The dark current flowing between the first electrode 21 and the second electrode 22 is reduced. The X-ray semiconductor detector 2 has improved detection accuracy with respect to the X-rays 30.

[0042] The manufacturing method of the X-ray semiconductor detector 2 of the present embodiment includes preparing an i-type nitride semiconductor substrate 10 having a first main surface 11 and a second main surface 12 opposite to the first main surface 11 (step S1). The first main surface 11 and the second main surface 12 are non-polar planes of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate 10 or planes inclined by an off-angle within 5° from the non-polar plane. The manufacturing method of the X-ray semiconductor detector 2 of the present embodiment includes forming a p-type semiconductor layer 16 on the first main surface 11 (step S2), forming an n-type semiconductor layer 17 on the second main surface 12 (step S3), forming a first electrode 21 on the p-type semiconductor layer 16 (step S4), and forming a second electrode 22 on the n-type semiconductor layer 17 (step S5).

[0043] Therefore, the plurality of through dislocations 15 extending from the first main surface 11 to the second main surface 12 are significantly reduced or eliminated. The dark current flowing between the first electrode 21 and the second electrode 22 is reduced. The X-ray semiconductor detector 2 has improved detection accuracy with respect to the X-rays 30.

[0044] In the manufacturing method of the X-ray semiconductor detector 2 of this embodiment, preparing the i-type nitride semiconductor substrate 10 (step S1) includes growing a nitride semiconductor ingot 33 on a growth substrate by the HVPE method (step S12). The main surface of the nitride semiconductor ingot 33 is the c-plane. Preparing the i-type nitride semiconductor substrate 10 (step S1) includes cutting the nitride semiconductor ingot 33 along the nonpolar surface of the nitride semiconductor crystal constituting the nitride semiconductor ingot 33 or a surface tilted by an off-angle of 5° or less from the nonpolar surface (step S13).

[0045] Therefore, the thickness of the nitride semiconductor ingot 33 increases compared to the case where the nitride semiconductor crystal is grown along the m-axis of the nitride semiconductor crystal. A large number of i-type nitride semiconductor substrates 10, which are of a size suitable for incorporation into the X-ray semiconductor detector 1, can be obtained from the nitride semiconductor ingot 33 with high productivity. The cost of the X-ray semiconductor detector 2 is reduced.

[0046] In the manufacturing method of the X-ray semiconductor detector 2 of this embodiment, the thickness of the nitride semiconductor ingot 33 is 1.0 mm or more.

[0047] Numerous i-type nitride semiconductor substrates 10, each of a size suitable for incorporation into the X-ray semiconductor detector 1, can be obtained from the nitride semiconductor ingot 33 with high productivity. This reduces the cost of the X-ray semiconductor detector 2.

[0048] In the manufacturing method of the X-ray semiconductor detector 2 of this embodiment, the m-plane of the nitride semiconductor crystal is a nonpolar plane of the nitride semiconductor crystal.

[0049] Therefore, multiple penetrating dislocations 15 extending from the first main surface 11 to the second main surface 12 are significantly reduced or eliminated. The dark current flowing between the first electrode 21 and the second electrode 22 is reduced. The X-ray semiconductor detector 2 has improved detection accuracy for X-rays 30.

[0050] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description and is intended to include all modifications within the meaning and scope of the claims equivalents.

[0051] 1 X-ray semiconductor detection device, 2 X-ray semiconductor detector, 2a, 2b, 2c pixels, 3 circuit board, 4 detection circuit, 10 type nitride semiconductor substrate, 11 first main surface, 12 second main surface, 13, 14 side surfaces, 15 through dislocation, 16 p-type semiconductor layer, 17 n-type semiconductor layer, 21 first electrode, 22 second electrode, 25 voltage source, 30 X-ray, 33 nitride semiconductor ingot, 34, 35 main surfaces, 36 nitride semiconductor piece.

Claims

1. A semiconductor X-ray detector comprising: an i-type nitride semiconductor substrate having a first main surface and a second main surface opposite to the first main surface; a p-type semiconductor layer formed on the first main surface; an n-type semiconductor layer formed on the second main surface; a first electrode formed on the p-type semiconductor layer; and a second electrode formed on the n-type semiconductor layer, wherein the first and second main surfaces are nonpolar surfaces of the nitride semiconductor crystal constituting the i-type nitride semiconductor substrate or surfaces tilted by an off-angle of 5° or less from the nonpolar surface.

2. The semiconductor X-ray detector according to claim 1, wherein the nonpolar surface of the nitride semiconductor crystal is the m-plane of the nitride semiconductor crystal.

3. A method for manufacturing a semiconductor X-ray detector, comprising: preparing an i-type nitride semiconductor substrate having a first main surface and a second main surface opposite to the first main surface, wherein the first and second main surfaces are nonpolar surfaces of a nitride semiconductor crystal constituting the i-type nitride semiconductor substrate or surfaces inclined by an off-angle of 5° or less from the nonpolar surface; forming a p-type semiconductor layer on the first main surface; forming an n-type semiconductor layer on the second main surface; forming a first electrode on the p-type semiconductor layer; and forming a second electrode on the n-type semiconductor layer.

4. The method for manufacturing a semiconductor X-ray detector according to claim 3, wherein preparing the i-type nitride semiconductor substrate includes growing a nitride semiconductor ingot on a growth substrate by the HVPE method, wherein the main surface of the nitride semiconductor ingot is the c-plane, and the nitride semiconductor ingot is cut along the nonpolar surface of the nitride semiconductor crystal constituting the nitride semiconductor ingot or along the surface tilted by an off-angle of 5° or less from the nonpolar surface.

5. The method for manufacturing a semiconductor X-ray detector according to claim 4, wherein the thickness of the nitride semiconductor ingot is 1.0 mm or more.

6. The method for manufacturing a semiconductor X-ray detector according to any one of claims 3 to 5, wherein the nonpolar surface of the nitride semiconductor crystal is the m-plane of the nitride semiconductor crystal.

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