Method for detecting shallow level impurities in ultra-high purity germanium single crystal

Abstract

The present application relates to the technical field of single crystal impurity detection, and specifically discloses a detection method for shallow energy level impurities of ultrahigh-purity germanium single crystal. After pretreatment of a germanium single crystal sample, photoetching, electron beam evaporation, annealing treatment and ohmic contact treatment are sequentially performed to obtain a sample to be detected, the sample to be detected is placed into a photo thermal ionization spectrometer, photo thermal ionization spectrum of the sample to be detected is obtained, and the impurity type and concentration of shallow energy level impurities of the ultrahigh-purity germanium single crystal are obtained by comparing the spectral line position and intensity of the elements. In the present application, a metal indium film is grown on the upper surface of the germanium single crystal, and the germanium single crystal can detect shallow energy level impurities in the photo thermal ionization spectrometer without adding conductive substances to the lower surface. Meanwhile, the present application uses an acid washing solution with high nitric acid content to perform acid washing treatment on the germanium single crystal, so that the germanium single crystal after acid washing can be tightly combined with the indium film evaporated by the electron beam, and the sample with the indium film loaded on the upper surface prepared has good ohmic contact characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single crystal impurity detection, and specifically discloses a detection method for shallow energy level impurities of ultrahigh-purity germanium single crystal. BACKGROUND

[0002] The purity of ultrahigh-purity germanium material can reach 13N, and it belongs to ultrahigh-purity metal material. It is a new material for a germanium detection system for nuclear radiation, and is particularly important for the detection of nuclear radiation in the process of nuclear technology application. The nuclear radiation detector taking ultrahigh-purity germanium single crystal as the core material is widely used in military, quasi-military and civilian fields. In the military, it is mainly used for safety monitoring of nuclear power and storage of nuclear military capabilities such as nuclear bombs. In quasi-military, it is mainly used in customs, justice, progress, etc. In civil, it is mainly used for safety monitoring of nuclear power plants. For ultrahigh-purity germanium single crystal, impurity detection is a key step for normal use of ultrahigh-purity germanium single crystal.

[0003] Impurities in ultrahigh-purity germanium single crystal are mainly divided into deep energy level and shallow energy level impurities. The existing technology ([1] Gu Xiaoying, Zhao Qingsong, Niu Xiaodong, et al. Preparation and performance of 13N ultrahigh-purity germanium single crystal [J]. Journal of Artificial Crystals, 2024, 53(03): 497-502. DOI: 10.16553 / j.cnki.issn1000-985x.20240012.001.) has disclosed a detection method for deep energy level impurities of ultrahigh-purity germanium single crystal. The article specifically discloses that a tin film is sputtered on the front surface of the germanium crystal as an electrode, a copper sheet is connected to the back surface of the germanium crystal by a tin foil, and an annealing treatment is performed in an annealing environment below 300 DEG C to obtain a to-be-tested ohmic electrode, and then a deep energy level impurity detection method is performed. However, the to-be-tested ohmic electrode prepared by the method disclosed in the article, that is, the tin film plated on the front surface of the germanium crystal and the copper sheet connected to the back surface of the germanium crystal by the tin foil through annealing treatment, can only be applied to the detection of deep energy level impurities, and cannot detect shallow energy level impurities in the germanium crystal. Therefore, it is of great significance to develop a detection method for shallow energy level impurities of ultrahigh-purity germanium single crystal for the preparation and performance research of ultrahigh-purity germanium material. SUMMARY

[0004] In view of the lack of a detection method for shallow energy level impurities of ultrahigh-purity germanium single crystal in the prior art, the present application provides a detection method for shallow energy level impurities of ultrahigh-purity germanium single crystal.

[0005] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0006] The first aspect of the present application provides a detection method for shallow energy level impurities of ultrahigh-purity germanium single crystal, comprising the following steps:

[0007] Step one, the germanium monocrystal sample is sequentially cut, ground, washed, dried, pickled, polished, washed and dried to obtain a pretreated sample, the pickling solution is nitric acid and hydrofluoric acid with a volume ratio of (2-4):1,

[0008] The mass percentage concentration of the nitric acid is 60%-80%, and the mass percentage concentration of the hydrofluoric acid is 30%-50%.

[0009] Step two, a positive photoresist is coated on the surface of the pretreated sample, dried, and photoetched to obtain a first treated sample.

[0010] Step three, a metal indium film is grown on the surface of the first treated sample by electron beam evaporation under an inert atmosphere to obtain a second treated sample.

[0011] Step four, the second treated sample is immersed in a polar organic solvent to peel off the photoresist layer, and the sample with the metal indium film loaded on the upper surface is obtained through solid-liquid separation; the sample with the metal indium film loaded on the upper surface is annealed under an inert atmosphere to obtain a to-be-tested sample.

[0012] Step five, the to-be-tested sample is placed in a photothermal ionization spectrometer to test the photothermal ionization spectrum of the to-be-tested sample, and the impurity type and concentration of the shallow energy level impurity of the ultrahigh-purity germanium monocrystal are obtained by comparing the spectral line position and intensity of the elements.

[0013] The present application grows a metal indium film on the upper surface of the germanium monocrystal without adding conductive substances to the lower surface, so that the germanium monocrystal can be detected for shallow energy level impurities in the photothermal ionization spectrometer, and also has good ohmic contact characteristics at a deep low temperature. In addition, the present application uses an acid pickling solution with a high nitric acid content to pickling the germanium monocrystal, so that the pickled germanium monocrystal can be tightly combined with the indium film evaporated by an electron beam, and the sample with the indium film loaded on the upper surface prepared has good ohmic contact characteristics.

[0014] Preferably, in step four, the annealing process specifically includes the following steps:

[0015] The sample with the metal indium film loaded on the upper surface is heated from a first temperature to a second temperature, and the temperature is kept constant to complete one heating, and the above heating process is repeated multiple times until the temperature of the sample with the metal indium film loaded on the upper surface is 480-520 DEG C, and the to-be-tested sample is obtained; the first temperature is in the range of 230-270 DEG C; the second temperature is 45-55 DEG C higher than the first temperature.

[0016] The present application uses a programmed temperature annealing method to tightly combine the metal indium film on the surface of the sample.

[0017] Preferably, the heating rate from the first temperature to the second temperature is 5-10 DEG C / min.

[0018] / min; the insulation time is 50s-70s.

[0019] By limiting the first temperature, the present invention avoids damage to the indium film due to excessively high temperatures, and also avoids ineffective annealing due to excessively low temperatures. In addition, by limiting the heating rate and holding time, the present invention further improves the tightness of the bonding between the metal indium film and the sample.

[0020] Preferably, in step 1, the thickness of the cut germanium single crystal sample is 3 mm to 5 mm, and the dislocation density is 100 cm -2 -5000cm -2 Between, carrier concentration ≤ 2E10cm -3 .

[0021] The present invention can ensure that the single crystal sample has fewer impurities by limiting the thickness, dislocation density and carrier concentration of the single crystal sample, thereby ensuring the purity of the single crystal of the sample to be tested prepared subsequently.

[0022] Preferably, in step 1, the polishing time is 1 min-2 min.

[0023] The present invention improves the surface flatness of the single crystal sample by limiting the time of pickling and polishing.

[0024] Preferably, in step 2, the coating is performed by spin coating, and the rotation speed of the spin coating is 1000 rpm-2000 rpm.

[0025] The present invention limits the coating method to spin coating and limits the rotation speed of the spin coating to ensure the smoothness of the coating.

[0026] Preferably, in step 2, the coating thickness of the positive photoresist is 1.5 μm-2 μm.

[0027] The present invention limits the coating thickness to spin coating, thereby preventing the coating thickness of the photoresist from being too thick or too thin, thereby causing poor photolithography effect.

[0028] Preferably, in step 2, the drying temperature is 90° C.-110° C., and the drying time is 1 min-3 min.

[0029] The present invention can ensure excellent drying effect of the photoresist by limiting the drying temperature and time.

[0030] Preferably, in step 2, the photolithography temperature is 25° C.-30° C., and the photolithography time is 50 s-80 s.

[0031] The present invention can ensure excellent photolithography effect by limiting the temperature and time of photolithography.

[0032] Preferably, in step three, the temperature of the electron beam evaporation is 160°C-200°C.

[0033] Preferably, in step three, the thickness of the metal indium film is 100-150 nm.

[0034] The present invention can ensure that the sample to be tested has good ohmic contact characteristics by limiting the temperature of electron beam evaporation and the thickness of the metal indium film.

[0035] Preferably, in step 4, the polar organic solvent is acetone.

[0036] The present invention can ensure that the sample to be tested has good ohmic contact characteristics by limiting the type of polar organic solvent.

[0037] Preferably, in step five, the test conditions of the photothermal ionization spectroscopy are: vacuum degree less than 0.3 kPa, and temperature of 4K-10K.

[0038] The present invention can ensure the detection of shallow energy level impurities in ultra-high purity germanium single crystals by limiting the test conditions of the photothermal ionization spectrum.

[0039] Preferably, the photothermal ionization spectrometer includes a Fourier transform infrared spectrometer, a Michelson interferometer, a refrigeration system, a temperature control and measurement system, a preamplifier, a filter, an oscilloscope and a computer system.

[0040] The present invention analyzes the types and relative contents of shallow energy level impurities in single crystals by limiting the device of the photothermal ionization spectrometer, thereby solving the problem that the prior art cannot detect and confirm shallow energy level impurities in ultra-high purity germanium single crystals.

[0041] Beneficial effects:

[0042] 1. The present invention grows a metallic indium film on the upper surface of a germanium single crystal, eliminating the need for adding a conductive material to the lower surface. This allows the germanium single crystal to detect shallow-level impurities in a photothermal ionization spectrometer, while also ensuring good ohmic contact properties at very low temperatures. Furthermore, the present invention utilizes an acid wash solution containing a high nitric acid content to pickle the germanium single crystal, allowing the pickled germanium single crystal to tightly bond with the electron beam evaporated indium film, ensuring that the prepared sample with the indium film on its upper surface has good ohmic contact properties. The present invention utilizes the aforementioned sample with the indium film on its upper surface to detect shallow-level impurities, resolving the problem of prior art inability to detect and confirm shallow-level impurities in ultra-high-purity germanium single crystals.

[0043] 2, The present application utilizes the method of polishing and pickling polishing to pretreat the single crystal sample, can guarantee the surface of the pretreated sample is flat, no cutting damage and scratch, and the present application limits the pickling to utilize the pickling solution with high nitric acid content, can make the germanium single crystal after pickling can be closely combined with the indium film evaporated by the electron beam, guarantee the sample with the indium film on the upper surface prepared has good ohmic contact characteristics.

[0044] 3, The present application can effectively guide the improvement of the single crystal production front process by confirming the shallow level impurity, the impurity is removed in the direction, and then the purity of the single crystal is improved, the technical support is provided for mass production 13N ultra-pure germanium single crystal, and a new test basis is provided for the preparation of 13N ultra-pure germanium single crystal. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The detection process flow chart of the shallow level impurity of the ultra-pure germanium single crystal in example 1 is provided.

[0046] Figure 2 The schematic diagram of the sample to be tested provided in example 1 is provided.

[0047] Figure 3 The Hall test curve of the sample to be tested in example 1 at liquid nitrogen temperature is provided.

[0048] Figure 4 The system block diagram of the photo thermal ionization spectrometer is provided.

[0049] Figure 5 The photo thermal ionization spectrum of the main shallow level impurity of the sample to be tested in example 1 at 7.5K is provided. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described below, obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0051] The present application provides a kind of detection method of shallow level impurity of ultra-pure germanium single crystal, this kind of detection method is pretreated to single crystal sample, in turn photoetching, electron beam evaporation, annealing treatment and ohmic contact processing, obtain the sample to be tested, the sample to be tested is placed in photo thermal ionization spectrometer, obtains the photo thermal ionization spectrum of the sample to be tested, compares the spectral line position and intensity of element, obtains the impurity type and concentration of shallow level impurity of ultra-pure germanium single crystal.

[0052] In the present application, the system block diagram of the photo thermal ionization spectrometer is as shown in Figure 4 As shown in Figure 4It can be seen that the photo thermal ionization spectrometer described in the application comprises a Fourier transform infrared spectrometer, a Michelson interferometer, a refrigeration system, a temperature control measurement system, a preamplifier, a filter, an oscilloscope and a computer system.

[0053] Embodiment 1

[0054] A method for detecting shallow energy level impurities in ultra-high purity germanium single crystals, comprising the following steps:

[0055] Step one, select a P-type germanium single crystal sample with a size of 7mm x 7mm x 3mm, a carrier concentration ≤2E10cm -3 , and a dislocation density of 2300cm -2 , carefully grind the P-type single crystal sample on a smooth glass plate using coarse to fine diamond grinding powder, add an appropriate amount of deionized water during grinding, grind until the sample surface is free of cutting damage and scratches, the surface is smooth, use ultrapure water to rinse clean and then dry with nitrogen, then polish the dried P-type single crystal sample with an acid solution mixed from a 70% mass percentage nitric acid solution and a 40% mass percentage hydrofluoric acid solution in a volume ratio of 3:1 for 2min, until the sample surface is smooth and bright, wash the polished sample with ultrapure water to neutral, then dry with nitrogen, and obtain a pretreated sample;

[0056] Step two, coat a layer of B1500 positive photoresist on the surface of the pretreated sample by spin coating, bake at 100℃ for 2min after spin coating, then perform photolithography on the sample to expose the part where the front electrode needs to be grown, and obtain a first treated sample; wherein the spin coating speed is 1000rpm;

[0057] Step three, place the first treated sample in an electron beam evaporation device under an inert atmosphere, place metal indium, and vacuumize to below 5x10 -4 Pa, grow a metal thin film on the surface of the first treated sample by electron beam evaporation, and obtain a second treated sample;

[0058] Step four, immerse the second processing sample in acetone for 5 min, use a disposable pipette to suck the acetone to impact the surface of the sample, peel off the photoresist and the upper metal, and separate the solid and the liquid to obtain a sample with a surface loaded indium film; the sample with the surface loaded indium film is heated to 300℃ at a heating rate of 5℃ / min under an argon atmosphere at 250℃, and then heated to 350℃ at a heating rate of 5℃ / min, and then heated to 400℃ at a heating rate of 5℃ / min, and then heated to 450℃ at a heating rate of 5℃ / min, and then heated to 500℃ at a heating rate of 5℃ / min, and then kept at 500℃ for 60 s, and then a to-be-tested sample is obtained; the IV curve of the sample at room temperature and liquid nitrogen temperature is tested by using a Hall tester, and after proving that the ohmic contact of the sample is qualified, the photothermal ionization spectroscopy test is prepared to be carried out;

[0059] Step five, the to-be-tested sample is placed into a photothermal ionization spectrometer, a probe is placed on an ohmic electrode, the sample bin is vacuumized to 3 mbar, then a refrigerator is started to be cooled to 4K, and then the test is carried out; first, the photothermal ionization spectrum at different temperature values (the temperature step is increased by 0.5K each time) in the interval of 5K-10K is tested to determine the optimal test temperature, and then a curve with a stable signal in an excited state, a relatively large intensity and a relatively small noise is selected for analysis.

[0060] The current-voltage characteristic test of the to-be-tested sample in Example 1 is carried out, and the test result is as shown in Figure 3 It can be seen from Figure 3 that the current-voltage (IV) characteristic of the to-be-tested sample in Example 1 is linear, and it can be proved that the to-be-tested sample in Example 1 also has good ohmic characteristics at low temperature, and can meet the requirements of photothermal ionization spectroscopy test. The photothermal ionization spectroscopy detection of the to-be-tested sample in Example 1 is carried out, and the test result is as shown in Figure 5 It can be seen from Figure 5 that the wavelength range corresponding to the excitation state transition of the shallow impurity is divided into two groups of spectral lines, which corresponds to the transition from the ground state to the excited state of the shallow acceptor impurity, and it can be known that the two shallow acceptor impurities are B and Al. According to the relative proportion of the spectral line intensity of the two impurities, the concentration ratio of the two impurities is estimated, and according to the net impurity concentration obtained by the Hall test, the relative proportion of the spectral line intensity, the approximate content of the two impurities can be inferred. It can be seen from this that the detection method provided in Example 1 of the present application can analyze the type and relative content of the shallow energy level impurities in the single crystal, and solves the problem that the shallow energy level impurities in the super-high-purity germanium single crystal cannot be detected and confirmed in the prior art.

[0061] Example 2

[0062] A method for detecting shallow-level impurities in an ultra-high-purity germanium single crystal comprises the following steps:

[0063] Step 1: Select a size of 8mm×8mm×4mm, with a carrier concentration of ≤2E10cm -3 , the dislocation density is 150cm -2 The P-type germanium single crystal sample is carefully ground on a smooth and flat glass plate using diamond abrasive powder from coarse to fine. An appropriate amount of deionized water is added during grinding until the sample surface is free of cutting damage and scratches and the surface is flat. Ultrapure water is used to rinse it and then it is blown dry with nitrogen. The dried P-type single crystal sample is then polished for 2 minutes with an acid solution mixed with a mass percentage concentration of 70% nitric acid solution and a mass percentage concentration of 40% hydrofluoric acid solution in a volume ratio of 3:1 until the sample surface is flat and bright. The polished sample is washed with ultrapure water until it is neutral, and then it is blown dry with nitrogen to obtain a pretreated sample.

[0064] Step 2: Spin-coating a layer of B1500 positive photoresist with a thickness of 2000 rpm on the surface of the pre-treated sample, baking the sample at 100°C for 2 minutes, and then performing photolithography on the sample to reveal the portion where the front electrode needs to be grown, thereby obtaining a first treated sample; wherein the spin-coating speed is 2000 rpm;

[0065] Step 3: In an inert atmosphere, place the first treated sample into an electron beam evaporation device, add metal indium, and evacuate to 5×10 -4 below Pa, growing a metal thin film on the surface of the first treated sample by electron beam evaporation to obtain a second treated sample;

[0066] Step 4, immersing the second treated sample in acetone for 5 minutes, using a disposable pipette to absorb acetone to impact the sample surface, stripping the photoresist and the upper metal, solid-liquid separation, and obtaining a sample with a surface-loaded metal indium film; the sample with the surface-loaded metal indium film is heated to 320°C at a heating rate of 10°C / min in an argon atmosphere of 270°C, and kept warm for 70 seconds, then heated to 370°C at a heating rate of 5°C / min, and kept warm for 70 seconds, then heated to 420°C at a heating rate of 5°C / min, and kept warm for 70 seconds, then heated to 470°C at a heating rate of 5°C / min, and kept warm for 70 seconds, then heated to 520°C at a heating rate of 5°C / min, and kept warm for 70 seconds to obtain a sample to be tested; using a Hall tester to test the IV curve of the sample at room temperature and liquid nitrogen temperature, it is proved that the sample ohmic contact is qualified and ready for photothermal ionization spectroscopy test;

[0067] Step 5. Place the sample to be tested in a photothermal ionization spectrometer, place the probe on the ohmic electrode, evacuate the sample chamber to 3 mbar, then turn on the refrigerator to cool it to 4K, and then test it. First, test the photothermal ionization spectrum at different temperature values ​​in the range of 5K-10K (each temperature step is 0.5K) to determine the optimal test temperature, and then select the curve with stable excited state signal, relatively large intensity, and relatively small noise for analysis.

[0068] Example 3

[0069] A method for detecting shallow-level impurities in an ultra-high-purity germanium single crystal comprises the following steps:

[0070] Step 1: Select a size of 8mm×7mm×3mm, with a carrier concentration of ≤2E10cm -3 , the dislocation density is 5000cm -2 The P-type germanium single crystal sample is carefully ground on a smooth and flat glass plate using diamond abrasive powder from coarse to fine. An appropriate amount of deionized water is added during grinding until the sample surface is free of cutting damage and scratches and the surface is flat. Ultrapure water is used to rinse it and then it is blown dry with nitrogen. The dried P-type single crystal sample is then polished for 2 minutes with an acid solution mixed with a mass percentage concentration of 70% nitric acid solution and a mass percentage concentration of 40% hydrofluoric acid solution in a volume ratio of 3:1 until the sample surface is flat and bright. The polished sample is washed with ultrapure water until it is neutral, and then it is blown dry with nitrogen to obtain a pretreated sample.

[0071] Step 2: Spin-coat a layer of B1500 positive photoresist on the surface of the pretreated sample, bake it at 100°C for 2 minutes, and then perform photolithography on the sample to expose the portion where the front electrode needs to be grown, thereby obtaining a first treated sample; wherein the spin-coating speed is 1500 rpm;

[0072] Step 3: In an inert atmosphere, place the first treated sample into an electron beam evaporation device, add metal indium, and evacuate to 5×10 -4 below Pa, growing a metal thin film on the surface of the first treated sample by electron beam evaporation to obtain a second treated sample;

[0073] Step 4, immersing the second treated sample in acetone for 5 minutes, using a disposable pipette to absorb acetone to impact the sample surface, stripping the photoresist and the upper metal, solid-liquid separation, and obtaining a sample with a surface-loaded metal indium film; the sample with the surface-loaded metal indium film is heated to 280°C at a heating rate of 5°C / min under an argon atmosphere of 230°C, and kept warm for 60 seconds, then heated to 330°C at a heating rate of 5°C / min, and kept warm for 60 seconds, then heated to 380°C at a heating rate of 5°C / min, and kept warm for 60 seconds, then heated to 430°C at a heating rate of 5°C / min, and kept warm for 60 seconds, then heated to 480°C at a heating rate of 5°C / min, and kept warm for 60 seconds to obtain a sample to be tested; using a Hall tester to test the IV curve of the sample at room temperature and liquid nitrogen temperature, it is proved that the sample ohmic contact is qualified and ready for photothermal ionization spectroscopy test;

[0074] Step 5. Place the sample to be tested into a photothermal ionization spectrometer, place the probe on the ohmic electrode, evacuate the sample chamber to 3 mbar, then turn on the refrigerator to cool it to 4K, and then test it. First, test the photothermal ionization spectrum at different temperature values ​​in the range of 5K-10K (each time the temperature step is increased by 0.5K) to determine the optimal test temperature, and then select the curve with stable excited state signal, relatively large intensity, and relatively small noise for analysis.

[0075] Example 4

[0076] A method for detecting shallow-level impurities in an ultra-high-purity germanium single crystal comprises the following steps:

[0077] Step 1: Select a size of 8mm×8mm×3mm, with a carrier concentration of ≤2E10cm -3 , dislocation density is 100-5000cm -2 The N-type germanium single crystal sample is carefully ground on a smooth and flat glass plate using diamond abrasive powder from coarse to fine. An appropriate amount of deionized water is added during grinding until the sample surface is free of cutting damage and scratches and the surface is flat. Ultrapure water is used to rinse and then blown dry with nitrogen. The dried P-type single crystal sample is then polished for 2 minutes with an acid solution mixed with a mass percentage concentration of 70% nitric acid solution and a mass percentage concentration of 40% hydrofluoric acid solution in a volume ratio of 3:1 until the sample surface is flat and bright. The polished sample is washed with ultrapure water until it is neutral, and then blown dry with nitrogen to obtain a pretreated sample.

[0078] Step 2: Spin-coat a layer of B1500 positive photoresist on the surface of the pretreated sample, bake it at 100°C for 2 minutes, and then perform photolithography on the sample to expose the portion where the front electrode needs to be grown, thereby obtaining a first treated sample; wherein the spin-coating speed is 1500 rpm;

[0079] Step 3: In an inert atmosphere, place the first treated sample into an electron beam evaporation device, add metal indium, and evacuate to 5×10 -4 below Pa, growing a metal thin film on the surface of the first treated sample by electron beam evaporation to obtain a second treated sample;

[0080] Step 4, immersing the second treated sample in acetone for 5 minutes, using a disposable pipette to absorb acetone to impact the sample surface, stripping the photoresist and the upper metal, solid-liquid separation, and obtaining a sample with a surface-loaded metal indium film; the sample with the surface-loaded metal indium film is heated to 300°C at a heating rate of 5°C / min under an argon atmosphere of 250°C, and kept warm for 60 seconds, then heated to 350°C at a heating rate of 5°C / min, and kept warm for 60 seconds, then heated to 400°C at a heating rate of 5°C / min, and kept warm for 60 seconds, then heated to 450°C at a heating rate of 5°C / min, and kept warm for 60 seconds, then heated to 500°C at a heating rate of 5°C / min, and kept warm for 60 seconds to obtain a sample to be tested; using a Hall tester to test the IV curve of the sample at room temperature and liquid nitrogen temperature, it is proved that the sample ohmic contact is qualified and ready for photothermal ionization spectroscopy test;

[0081] Step 5. Place the sample to be tested into a photothermal ionization spectrometer, place the probe on the ohmic electrode, evacuate the sample chamber to 3 mbar, then turn on the refrigerator to cool it to 4K, and then test it. First, test the photothermal ionization spectrum at different temperature values ​​in the range of 5K-10K (each time the temperature step is increased by 0.5K) to determine the optimal test temperature, and then select the curve with stable excited state signal, relatively large intensity, and relatively small noise for analysis.

[0082] It can be seen from Examples 1-4 that the detection method provided by the present invention is capable of analyzing the types and relative contents of shallow energy level impurities in different crystal types of germanium single crystals (P-type single crystals and N-type single crystals), thereby solving the problem that the existing technology is unable to detect and confirm shallow energy level impurities in ultra-high purity germanium single crystals.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting shallow-level impurities in ultra-high purity germanium single crystals, characterized by: The steps include: Step 1: Cutting, grinding, cleaning, drying, pickling, polishing, cleaning and drying the germanium single crystal sample in sequence to obtain a pretreated sample, wherein the pickling solution is nitric acid and hydrofluoric acid in a volume ratio of (2-4):1, wherein the mass percentage concentration of the nitric acid is 60%-80%; the mass percentage concentration of the hydrofluoric acid is 30%-50%; Step 2: coating a positive photoresist on the surface of the pre-treated sample, drying, and photolithography to obtain a first treated sample; Step 3: growing a metal indium film on the surface of the first treated sample by electron beam evaporation in an inert atmosphere to obtain a second treated sample; Step 4: Immerse the second treated sample in a polar organic solvent, peel off the photoresist layer, separate the solid and liquid, and obtain a sample with a metal indium film loaded on the upper surface; anneal the sample with the metal indium film loaded on the upper surface under an inert atmosphere to obtain a sample to be tested, wherein the annealing treatment specifically includes the following steps: heating the sample with the metal indium film loaded on the upper surface from a first temperature to a second temperature, keeping the temperature, completing one heating, repeating the above heating process multiple times until the temperature of the sample with the metal indium film loaded on the upper surface is 480°C-520°C, to obtain a sample to be tested; the temperature range of the first temperature is 230°C-270°C; the second temperature is 45°C-55°C higher than the first temperature; Step 5: Place the sample to be tested into a photothermal ionization spectrometer to obtain the impurity type and concentration of shallow energy level impurities in the ultra-high purity germanium single crystal.

2. The method for detecting shallow-level impurities in an ultra-high purity germanium single crystal according to claim 1, wherein: The heating rate from the first temperature to the second temperature is 5°C / min-10°C / min; the insulation time is 50s-70s.

3. The method for detecting shallow-level impurities in an ultra-high purity germanium single crystal according to claim 1, wherein: In step 1, the thickness of the cut germanium single crystal sample is 3 mm to 5 mm, the dislocation density is between 100 cm-2 and 5000 cm-2, and the carrier concentration is ≤ 2E10 cm-3; and / or In step 1, the polishing time is 1 min-2 min.

4. The method for detecting shallow-level impurities in an ultra-high purity germanium single crystal according to claim 1, wherein: In step 2, the coating is performed by spin coating at a rotation speed of 1000 rpm to 2000 rpm; and / or In step 2, the coating thickness of the positive photoresist is 1.5 μm-2 μm.

5. The method for detecting shallow-level impurities in an ultra-high purity germanium single crystal according to claim 1, wherein: In step 2, the drying temperature is 90°C-110°C, and the drying time is 1 min-3 min; and / or In step 2, the photolithography temperature is 25° C.-30° C., and the photolithography time is 50 s-80 s.

6. The method for detecting shallow-level impurities in an ultra-high purity germanium single crystal according to claim 1, wherein: In step 3, the temperature of the electron beam evaporation is 160° C.-200° C.; and / or In step three, the thickness of the metal indium film is 100nm-150nm.

7. The method for detecting shallow-level impurities in an ultra-high purity germanium single crystal according to claim 1, wherein: In step 5, the test conditions of the photothermal ionization spectroscopy are: vacuum degree <0.3 KPa, temperature 4K-10K.

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