阅读说明：本技术 探测介质及其制备方法、金刚石探测器 (Detection medium, preparation method thereof and diamond detector ) 是由 江南 林正得 杨明阳 高靖尧 戴丹 于 2019-03-21 设计创作，主要内容包括：本发明涉及一种探测介质及其制备方法、金刚石探测器,所述制备方法包括：提供单晶的金刚石基体；采用激光直写金刚石基体的表面,使金刚石原位转化生成石墨层,其中,石墨层的表面低于金刚石基体的表面而形成自金刚石基体表面延伸至石墨层的沟槽,沟槽的宽度为1μm～60μm,深度为20μm～100μm,长度不小于金刚石基体的表面的最短尺寸的1/4；以及在金刚石基体上外延生长单晶金刚石层,并使单晶金刚石层至少覆盖石墨层,得到探测介质。本发明获得的探测介质中,起探测作用的为单晶金刚石层,增大了用于探测响应的金刚石的有效面积。将本发明的探测介质应用于金刚石探测器时,可提高金刚石探测器对外部可响应信号的灵敏度。(The invention relates to a detection medium, a preparation method thereof and a diamond detector, wherein the preparation method comprises the following steps: providing a single crystal diamond substrate; directly writing the surface of a diamond matrix by laser to convert the diamond in situ to generate a graphite layer, wherein the surface of the graphite layer is lower than the surface of the diamond matrix to form a groove extending from the surface of the diamond matrix to the graphite layer, the width of the groove is 1-60 mu m, the depth of the groove is 20-100 mu m, and the length of the groove is not less than 1/4 of the shortest dimension of the surface of the diamond matrix; and epitaxially growing a single crystal diamond layer on the diamond substrate, and enabling the single crystal diamond layer to at least cover the graphite layer to obtain the detection medium. In the detection medium obtained by the invention, the single crystal diamond layer plays a role in detection, and the effective area of the diamond for detection response is increased. When the detection medium is applied to a diamond detector, the sensitivity of the diamond detector to an external response signal can be improved.)

1. A method for preparing a detection medium is characterized by comprising the following steps:

providing a single crystal diamond substrate;

directly writing the surface of the diamond matrix by using laser to convert the diamond in situ to generate a graphite layer, wherein the surface of the graphite layer is lower than the surface of the diamond matrix to form a groove extending from the surface of the diamond matrix to the graphite layer, the width of the groove is 1-60 mu m, the depth of the groove is 20-100 mu m, and the length of the groove is not less than 1/4 of the shortest dimension of the surface of the diamond matrix; and

and epitaxially growing a single crystal diamond layer on the diamond substrate, and enabling the single crystal diamond layer to at least cover the graphite layer to obtain the detection medium.

2. The method for preparing a detection medium according to claim 1, wherein the length of the groove is 1/3-1/2 of the shortest dimension of the diamond substrate.

3. The method for preparing a detection medium according to claim 1, wherein the number of the grooves is plural, and the plural grooves are arranged on the same surface of the diamond substrate at intervals.

4. The method of claim 1, wherein the laser has a beam spot diameter of 1 μm to 10 μm.

5. The method for preparing a detection medium according to claim 1, wherein the power of the laser is 100w to 500w, and the scanning speed is 500mm/s to 1500 mm/s.

6. The method of preparing a detection medium according to claim 1, wherein a single crystal diamond layer is epitaxially grown on the diamond substrate using a microwave plasma chemical vapor deposition method.

7. The method of claim 6, wherein the flow rate of methane is 1sccm to 10sccm, the flow rate of hydrogen is 350sccm to 450sccm, and the pressure in the growth chamber is 15KPa to 17 KPa.

8. The method for preparing the detection medium according to claim 7, wherein in the microwave plasma chemical vapor deposition method, the growth temperature is 850-1000 ℃, the temperature rise time is 10-25 min, the growth time is 2-8 h, and the temperature drop time is not less than 25min after the growth is finished.

9. A detection medium obtained by the production method according to any one of claims 1 to 8, comprising a single-crystal diamond base body, a graphite layer embedded in the diamond base body, the graphite layer having a surface lower than the surface of the diamond base body and forming a groove extending from the surface of the diamond base body to the graphite layer, and a single-crystal diamond layer covering at least the graphite layer and filling the groove.

10. A diamond probe comprising the probe medium of claim 9.

Technical Field

The invention relates to the field of semiconductor detectors, in particular to a detection medium, a preparation method thereof and a diamond detector.

Background

The semiconductor detector is a radiation detector using a semiconductor material as a detection medium, and for the semiconductor detector prepared by using diamond as a material, no matter whether electron-hole carriers generated by the action of an external signal on the diamond are transmitted to an external circuit to form the collection of an electric signal or an electric field is applied to the electric signal to realize the recombination of internal electron-hole carrier pairs, a proper electrode needs to be added to the diamond, so that good electric contact-non-rectifying (ohmic) contact is formed between the electrode and the diamond.

However, diamond is easy to form Schottky (Schottky) rectifying contact due to interface barrier when contacting with metal because of large forbidden band width, and a general approach for overcoming Schottky contact is to form a multi-level gradient metal interface layer on the reaction surface of diamond to reduce the barrier. However, the multilayer electrode structure constructed on the reaction surface of the diamond can greatly hinder the sensitivity of the diamond to external response signals, so that the effective area of the reaction surface capable of responding to detection signals is greatly reduced, the dark current of a detector is increased, and the sensitivity of the detector is very unfavorable. Moreover, the diamond surface is difficult to realize high dosage doping, so that an electrode with good ohmic contact is difficult to manufacture on the diamond.

Disclosure of Invention

In view of the above, it is necessary to provide a detection medium, a method for preparing the same, and a diamond detector; in the detection medium obtained by the preparation method, the single crystal diamond layer plays a role in detection, so that the area of a reaction surface of the detection medium, which can respond to a detection signal, can be remarkably increased, the thickness of the single crystal diamond layer in the detection medium can be accurately controlled according to the requirement of the diamond detector, and the sensitivity of the obtained diamond detector to an external response signal is high.

A method of preparing a detection medium, comprising the steps of:

providing a single crystal diamond substrate;

directly writing the surface of the diamond matrix by using laser to convert the diamond in situ to generate a graphite layer, wherein the surface of the graphite layer is lower than the surface of the diamond matrix to form a groove extending from the surface of the diamond matrix to the graphite layer, the width of the groove is 1-60 mu m, the depth of the groove is 20-100 mu m, and the length of the groove is not less than 1/4 of the shortest dimension of the surface of the diamond matrix; and

and epitaxially growing a single crystal diamond layer on the diamond substrate, and enabling the single crystal diamond layer to at least cover the graphite layer to obtain the detection medium.

In one embodiment, the length of the groove is 1/3-1/2 of the shortest dimension of the diamond substrate.

In one embodiment, the number of the grooves is multiple, and the grooves are arranged on the same surface of the diamond substrate at intervals.

In one embodiment, the beam spot diameter of the laser is 1-10 μm.

In one embodiment, the power of the laser is 100 w-500 w, and the scanning speed is 500 mm/s-1500 mm/s.

In one embodiment, a microwave plasma chemical vapor deposition process is used to epitaxially grow a layer of single crystal diamond on the diamond substrate.

In one embodiment, the microwave plasma chemical vapor deposition method comprises a methane flow rate of 1sccm to 10sccm, a hydrogen flow rate of 350sccm to 450sccm, and a pressure in the growth chamber of 15KPa to 17 KPa.

In one embodiment, in the microwave plasma chemical vapor deposition method, the growth temperature is 850-1000 ℃, the temperature rise time is 10-25 min, the growth time is 2-8 h, and the temperature reduction time is not less than 25min after the growth is finished.

In one embodiment, the diamond matrix is a single crystal diamond matrix.

The detection medium is prepared by the preparation method and comprises a monocrystalline diamond substrate, a graphite layer and a monocrystalline diamond layer, wherein the graphite layer is embedded in the diamond substrate, the surface of the graphite layer is lower than the surface of the diamond substrate to form a groove extending from the surface of the diamond substrate to the graphite layer, and the monocrystalline diamond layer at least covers the graphite layer and fills the groove.

A diamond detector comprising a detection medium as described above.

In the preparation method of the present invention, diamond is converted into a graphite layer in situ on a diamond substrate having a single crystal structure by laser direct writing. Due to the fact that laser can process and wear away part of the diamond and the atomic arrangement of the diamond and graphite in the process of acting on the diamond, the surface of the graphite layer is lower than the surface of the diamond substrate to form the groove. And finally, epitaxially growing on the diamond substrate to obtain the single crystal diamond layer. The single crystal diamond layer at least covers the graphite layer, so that the graphite layer is arranged between the diamond matrix and the single crystal diamond layer in a buried layer mode, and the detection medium of the sandwich-like structure of the diamond matrix, the graphite layer and the single crystal diamond layer is obtained. In the detection medium, the graphite layer is used as an electrode, the single crystal diamond layer and the graphite layer can realize good ohmic contact, the surface of the single crystal diamond layer is exposed, the detection effect can be achieved, the effective area of a reaction surface, which can be responded by the detection medium to a detection signal, is increased, the sensitivity of the detection medium to an external response signal is improved, and therefore the problem that the effective area of the reaction surface, which can participate in detection response, of the diamond is small due to the fact that a multilayer electrode structure is constructed on the surface of the diamond in the prior art is solved. Meanwhile, the growth thickness of the monocrystalline diamond layer for detecting response can be accurately controlled according to the requirement of the detector.

Drawings

FIG. 1 is a process flow diagram of a method for preparing a detection medium according to the present invention;

FIG. 2 is a schematic view of another embodiment of the trench of the present invention;

FIG. 3 is a schematic view of the groove distribution on a diamond substrate according to the present invention;

FIG. 4 is an SEM image of a diamond substrate after laser direct writing in example 1 of the present invention;

FIG. 5 is a Raman spectrum of the diamond matrix after laser direct writing in example 1 of the present invention;

fig. 6 is a raman spectrum at a groove of a detection medium obtained in example 1 of the present invention;

FIG. 7 is an SEM image of a trench of a probe medium obtained in example 1 of the present invention;

FIG. 8 is a two-dimensional cross-sectional dimension view of a groove on a diamond substrate after laser direct writing in example 4 of the present invention;

fig. 9 is a two-dimensional cross-sectional dimension diagram at a trench of a detection medium obtained in embodiment 4 of the present invention.

In the figure: 10. a diamond matrix; 20. a graphite layer; 30. a trench; 40. a layer of single crystal diamond; 50. a square groove.

Detailed Description

The detection medium, the preparation method thereof and the diamond detector provided by the invention are further explained below.

As shown in fig. 1, the preparation method of the detection medium provided by the invention comprises the following steps:

s1, providing a single crystal diamond substrate 10;

s2, directly writing the surface of the diamond matrix 10 by laser to convert the diamond in situ to generate a graphite layer 20, wherein the surface of the graphite layer 20 is lower than the surface of the diamond matrix 10 to form a groove 30 extending from the surface of the diamond matrix 10 to the graphite layer 20, the groove 30 has a width of 1-60 μm, a depth of 20-100 μm and a length of 1/4 not less than the shortest dimension of the surface of the diamond matrix 10;

s3, epitaxially growing a single crystal diamond layer 40 on the diamond substrate 10, and covering at least the graphite layer 20 with the single crystal diamond layer 40 to obtain a detection medium.

In step S1, the shape of the surface of the diamond substrate 10 is not limited, and may be square, circular, or irregular. The size of the surface of the diamond substrate 10 is not limited, and the size of the surface of the diamond substrate 10 may be the length or width, the diameter, etc. of the surface of the diamond substrate 10.

The thickness of the diamond base material 10 is 0.1mm to 10mm, preferably 0.2mm to 5mm, and more preferably 0.3mm to 3mm in view of easy availability of the diamond base material 10 and manufacturing cost.

The single crystal diamond substrate 10 acts as an inducer when the single crystal diamond layer 40 is epitaxially grown on the single crystal diamond substrate 10. It is therefore possible to ensure that the single crystal diamond layer 40 is epitaxially grown on the diamond substrate 10, which may be a High Pressure High Temperature (HPHT) single crystal diamond substrate, a CVD single crystal diamond substrate, or the like, of the single crystal diamond substrate 10.

In step S2, the thickness and continuity of graphite layer 20 are achieved by controlling the power and scanning speed of the laser. Preferably, the power of the laser is 100 w-500 w, and the scanning speed is 500 mm/s-1500 mm/s, so that the conductivity test resistance of the graphite layer 20 is not higher than 30 Ω/cm, and the graphite layer can form good ohmic contact with the single crystal diamond layer 40 when used as an electrode.

The grooves 30 are formed by the fact that the laser wears away part of the diamond and the atomic arrangement of the diamond and graphite during the diamond action, so that the surface of the graphite layer 20 is lower than the surface of the diamond substrate 10.

The dimensions of the trench 30 are critical to the subsequent epitaxial growth to obtain a single crystal diamond layer. In the present invention, when the size of the groove 30 to which the laser is applied is controlled within the range of the size of the present invention, under appropriate growth parameters, the single crystal diamond is grown in a lateral cross growth method at the groove 30 due to the influence of the size effect.

In consideration of the processing precision of the laser and the simplicity of the manufacturing process, the width of the groove 30 is preferably 5 μm to 40 μm, the depth is preferably 30 μm to 60 μm, and the length is preferably 1/3 to 1/2 of the shortest dimension of the diamond matrix 10.

The size and pattern shape of the groove 30 are realized by controlling the laser beam spot diameter and the number of scanning times by a software program, and the beam spot diameter of the laser is preferably 1 μm to 10 μm, and more preferably 1 μm to 5 μm.

The structure of the groove 30 is not limited, and includes a rectangular shape as shown in fig. 1, a partial circular shape as shown in fig. 2, and the like in cross section.

Considering that the reaction gas has an etching effect on the graphite layer 20 during the epitaxial growth of the single crystal diamond layer 40 on the diamond substrate 10, the structure of the grooves 30 is preferably the structure shown in fig. 1, in which the grooves 30 have a regular size and damage of the reaction gas to the graphite layer 20 is reduced by the influence of the size boundary.

The number of the grooves 30 is plural, the grooves 30 are arranged on the same surface of the diamond substrate 10 at intervals, and the interval distance can be selected according to the size of the diamond substrate 10.

As shown in FIG. 3, 3 grooves 30 are arranged on the same surface of the diamond matrix 10 at intervals in parallel, the length of each groove 30 can penetrate through the whole surface of the diamond matrix 10 as shown in a, or is 1/3-1/2 of the shortest dimension of the diamond matrix 10 as shown in b. Or as shown in c, two ends of the groove 30 may be respectively communicated with a square groove 50 with a certain size to form a tool-shaped groove, and the size of the square groove 50 may also be selected according to the size of the diamond substrate 10.

Considering that polycrystalline diamond contains grain boundaries, which interfere with the transport of carriers, and affects the sensitivity and efficiency of the detector when applied to the detector, and single crystal diamond does not contain various irregular grain boundaries, and has a low defect density, the single crystal diamond layer 40 is epitaxially grown on the diamond substrate 10 in step S3 to ensure the sensitivity and efficiency of the detection medium of the present invention.

The microwave plasma chemical vapor deposition method (MPCVD method) can not only grow a high-quality single crystal diamond layer which is completely colorless and transparent and hardly contains any impurity, but also can accurately control the growth thickness of the single crystal diamond layer for detection response according to the requirement of the detector. Therefore, the present invention preferably epitaxially grows the single crystal diamond layer 40 on the diamond substrate 10 using the MPCVD method.

Specifically, prior to growing the single crystal diamond layer 40, the diamond matrix 10 with the grooves 30 is subjected to a pretreatment including an ultrasonic treatment in ethanol, acetone, or the like.

After the pretreatment is finished, the diamond matrix 10 with the grooves 30 is placed in a growth chamber of MPCVD equipment, and the growth chamber is vacuumized until the air pressure in the growth chamber is not higher than 1 × 10^-1Pa, and preheating for 1-2 min.

Then, hydrogen gas is introduced, and the flow rate of the hydrogen gas is 350sccm to 450sccm, preferably 380sccm to 420 sccm. Simultaneously, synchronously increasing the pressure of the growth chamber and the power of the microwave until the pressure in the chamber reaches 15KPa to 17KPa, preferably 15.5KPa to 16.5KPa, and further preferably 15.9KPa to 16.1 KPa; the temperature is 850 to 1000 ℃, preferably 900 to 970 ℃, and more preferably 930 to 960 ℃.

Considering the influence of the etching consumption of the hydrogen plasma generated under the action of the microwave on the graphite layer 20 in the temperature rising process, the temperature rising time is 10-25 min, preferably 15-20 min.

Then, methane gas is introduced for growth for 2 to 8 hours, preferably for 4 to 6 hours. Wherein the flow rate of methane is 1sccm to 10sccm, preferably 2sccm to 5 sccm.

After the growth is finished, the pressure of the growth chamber and the power of the microwave are synchronously reduced to the pressure and the temperature in the chamber until the closing end state.

Considering that the single crystal diamond layer 40 grown by epitaxy generates stress under the condition of excessively fast temperature reduction to cause cracks inside the single crystal diamond layer 40, the temperature reduction time after the growth is finished is not less than 25min, and the rate of the initial temperature reduction stage is as slow as possible.

Preferably, in the temperature raising and reducing stages, the power of the microwave and the pressure in the chamber are synchronously increased or reduced to the required process parameters in proportion.

According to the invention, firstly, diamond is converted into a graphite layer 20 in situ on a diamond matrix 10 through laser direct writing and a groove 30 is formed, then a single crystal diamond layer 40 is epitaxially grown on the diamond matrix 10 by adopting a microwave plasma chemical vapor deposition method, the groove 30 is filled and the formed graphite layer 20 is covered, so that the graphite layer 20 is arranged between the diamond matrix 10 and the single crystal diamond layer 40 in a buried layer manner, and further the detection medium of a sandwich-like structure of the diamond matrix 10-the graphite layer 20-the single crystal diamond layer 40 is obtained.

The invention also provides a detection medium which is obtained by the preparation method and comprises a monocrystalline diamond substrate 10, a graphite layer 20 and a monocrystalline diamond layer 40, wherein the graphite layer 20 is embedded in the diamond substrate 10, the surface of the graphite layer 20 is lower than the surface of the diamond substrate 10 to form a groove 30 extending from the surface of the diamond substrate 10 to the graphite layer 20, and the monocrystalline diamond layer 40 at least covers the graphite layer 20 and fills the groove 30.

Unlike the method of directly preparing an electrode on the surface of the diamond substrate 10, the single crystal diamond layer 40 serves as a detection medium obtained by the present invention, and the graphite layer 20 serves as an electrode having good ohmic contact with the single crystal diamond layer 40. Therefore, the detection medium obtained by the preparation method can avoid the problem that the effective area of the diamond surface which can participate in detection response is reduced because a multilayer electrode structure is constructed on the surface of the diamond substrate, and the effective area of the diamond surface for detection response is increased.

The invention also provides a diamond detector which comprises the detection medium.

The effective area of the diamond surface for detection response in the detection medium is large, the ohmic contact between the graphite layer and the single crystal diamond layer is good, and meanwhile, the growth thickness of the single crystal diamond layer for detection response can be accurately controlled according to the requirements of the detector. Therefore, the detection medium of the invention can improve the sensitivity and efficiency of the diamond detector to the external response signals.

Hereinafter, the detection medium, the method for manufacturing the same, and the diamond detector will be further described with reference to the following specific examples.