Compound semiconductor and method for manufacturing the same

Abstract

The present application provides a kind of zinc cadmium telluride (CdZnTe) single crystal, and its effective manufacturing method, the zinc cadmium telluride (CdZnTe) single crystal has the area of 100 mm 2 Above, and mobility lifetime product (μτ product) becomes 1.0×10 ‑3 cm 2 The area of 50% or more of the whole, i.e. in a wide range, the main surface becomes high μτ product.

Description

[0001] This application is a divisional application of Chinese PCT patent application number 2018800044294, entitled "Compound Semiconductor and Method of Manufacturing Thereof", filed on September 14, 2018. Technical Field

[0002] This invention relates to a compound semiconductor zinc cadmium telluride (CdZnTe) single crystal and its manufacturing method. Background Technology

[0003] Cadmium telluride (CdTe), a group II-VI semiconductor material composed of cadmium (Cd) from group II (2B) and tellurium (Te) from group VI (6B), is a semiconductor material with a large band gap (~1.44 eV). Furthermore, cadmium zinc telluride (CdZnTe), obtained by further widening the band gap by replacing a portion of the Cd in CdTe with zinc (Zn), is also a group II-VI semiconductor material similar to CdTe, and its properties can be effectively utilized for a wide range of applications.

[0004] Generally, when light strikes a semiconductor material, it excites some of the electrons within the semiconductor. If the energy of the light (photon energy) is greater than the band gap of the semiconductor, electrons in the valence band will cross the band gap and transition to the conductor, creating holes in the valence band and generating mobile charge (carrier) pairs. The phenomenon of generating carriers in a semiconductor material through the incident or irradiation of light in this way is called the (internal) photoelectric effect. After a certain period of time, due to charge recombination and other processes, the carriers generated through the photoelectric effect will be destroyed. The time until this destruction is called the carrier's "lifetime."

[0005] As described above, if the movable carriers generated through the photoelectric effect are extracted as an electrical signal, they can be used as "various semiconductor devices utilizing the photoelectric effect." In this case, the collection efficiency of the carriers extracted as electrical signals can be evaluated by the mobility-lifetime product (μτ product), which is the product of the carrier lifetime (τ) and the ease with which carriers move in the semiconductor material, i.e., the mobility (μ). That is, a semiconductor material with a higher μτ product is more likely to have a higher carrier collection efficiency, thus improving the device's performance.

[0006] The carrier mobility (μ) and carrier lifetime (τ) of the aforementioned semiconductor are significantly affected by factors such as the crystallinity or impurity-related states of the semiconductor material. Therefore, the aforementioned product, i.e., the μτ product, can be considered as an inherent material indicator that comprehensively reflects the characteristics of the semiconductor material. Thus, the μτ product can be used as an indicator for evaluating the inherent properties of semiconductor materials.

[0007] From this perspective, the μτ product can be used as an indicator to evaluate the performance of CdZnTe semiconductor materials. However, as background technology for mentioning the μτ product of CdZnTe materials, the following patent documents can be cited.

[0008] Background Technology Documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2013-241289 Patent Document 2: Japanese Patent Application Publication No. 2016-153362. Summary of the Invention

[0009] The problem that the invention aims to solve As mentioned earlier, the μτ product of semiconductor materials is a property that varies depending on the state and other characteristics related to crystallinity or impurities. CdZnTe, a mixed-crystal compound containing multiple group II-VI elements, is one of the crystalline materials that is difficult to stably grow into a bulk crystal with relatively uniform crystallization characteristics over a wide range. In this type of CdZnTe crystallization, the processing conditions during or after crystallization growth have a sensitive effect on the crystallization state; therefore, even slight differences in processing conditions can result in significant differences in crystallization characteristics. Consequently, in actual CdZnTe crystallization, even crystalline materials cut from the same region of the same ingot with the same cure rate exhibit different μτ products depending on the local crystallization location.

[0010] Therefore, in CdZnTe crystallization, it is necessary not only to obtain crystals with a high μτ product, but also to maximize the area of ​​crystallization where this high μτ product is obtained. If only a portion of the cut crystal surface yields the locally desired high μτ product, and a large portion of the crystal cannot be utilized, the yield will be significantly reduced.

[0011] The present invention is based on the above-mentioned problems and solves the following problems: it provides a CdZnTe single crystal material that achieves a high μτ product while increasing the proportion of regions on the same crystalline material surface that achieve the high μτ product.

[0012] Problem-solving methods To solve the above-mentioned technical problems, the inventors conducted intensive research and discovered that the μτ product of CdZnTe single crystals is not only greatly affected by the conditions during crystal growth, but also by the heat treatment temperature during the heat treatment after crystal growth. This significantly influences the size of the region with high μτ product. It can be seen that by appropriately and strictly controlling this condition, not only can a high μτ product be achieved, but also crystalline materials with high μτ products over a wide range can be obtained, thus completing the invention.

[0013] Based on the above insights, the present invention provides the following invention.

[0014] 1) A single crystal of zinc cadmium telluride (CdZnTe) with an area of ​​100 mm² 2 The above, and the mobility lifetime product (μτ product) becomes 1.0 × 10 -3 cm 2 The area above / V represents more than 50% of the main surface of the whole.

[0015] 2) As described in 1) above, the proportion of Zn in group II elements is 2.0 at% to 10.0 at%.

[0016] 3) Zinc cadmium telluride single crystal as described in 1) or 2) above, wherein the orientation of the main surface is {111} plane.

[0017] 4) A method for manufacturing zinc cadmium telluride single crystal, which is the method for manufacturing zinc cadmium telluride single crystal according to any one of 1) to 3) above, comprising: growing zinc cadmium telluride crystal ingot, directly heat-treating the grown zinc cadmium telluride crystal ingot in the form of an ingot, and cutting a single crystal from the heat-treated zinc cadmium telluride crystal ingot with a main face having a specific face orientation; the temperature of the heat treatment is above 800°C and below 1000°C, and the difference between the maximum temperature and the minimum temperature in the region between the upper end and the lower end of the single crystal ingot is within 20°C.

[0018] 5) The method for manufacturing zinc cadmium telluride single crystals as described in 4) above, wherein the growth method of the zinc cadmium telluride crystal ingot is the vertical gradient solidification (VGF) method.

[0019] 6) The method for manufacturing zinc cadmium telluride single crystals as described in 4) or 5) above, wherein after the single crystal ingot is grown, the zinc cadmium telluride crystal ingot is continuously heat-treated in the furnace in which the single crystal ingot is grown.

[0020] The effects of the invention According to the technology of the present invention, both increasing the μτ product in CdZnTe single crystal materials and increasing the proportion of high μτ product regions on the same surface can be achieved. Therefore, a large number of high μτ product single crystal substrates can be collected from the same crystal surface, which can be used as large-area high μτ product single crystal substrates. Thus, the manufacturing efficiency and product yield of components using CdZnTe single crystals can be improved, and product costs can be reduced. Attached Figure Description

[0021] Figure 1 This is a diagram illustrating an example of the CdZnTe crystallization growth furnace used in this invention.

[0022] Figure 2This is a graph showing an example of temperature distribution during heat treatment. Detailed Implementation

[0023] The CdZnTe single crystal of the present invention is a single crystal material containing at least cadmium (Cd), zinc (Zn), and tellurium (Te) as constituent elements. This single crystal material may also contain other dopant elements as needed. The shape of the single crystal material is not particularly limited, but it has at least one principal surface. Examples of such a crystal shape include plate-shaped substrates or wafers with a specific thickness (e.g., 500 μm or more, but not limited thereto). Furthermore, in the present invention, a "principal surface" refers to the surface with the largest area among the surfaces exposed in the crystalline material and which can be considered as a plane.

[0024] The CdZnTe single crystal of the present invention has a principal surface area of ​​at least 100 mm². 2 The above, and the product of μ and τ becomes 1.0 × 10 -3 cm 2 The area above / V represents more than 50% of the overall feature of the principal surface. If the area of ​​the principal surface of a CdZnTe single crystal is small, then, for example, 1.0 × 10 -3 cm 2 It is not particularly difficult technically to achieve or approach 100% of the region with a high μτ product of / V or higher. However, as is known from common technical knowledge, it is technically difficult to achieve a wide range of regions with high μτ products of the aforementioned level throughout the principal planes of a CdZnTe single crystal with a relatively large principal plane.

[0025] In this invention, 100 mm is set as the reference for the size of this main surface. 2 The above range. The size of the main surface used as the reference can be 400 mm, depending on the situation. 2 Above, or 1000 mm 2 The above, and even up to 10,000 mm 2 From the above, it can be easily deduced that the larger the lower limit of the area of ​​the principal surface that serves as the benchmark, the higher the improvement, such as 1.0 × 10⁻⁶. -3 cm 2 The greater the proportion of regions with high μτ products above / V, the more technically difficult it becomes.

[0026] Furthermore, in this invention, the index for "high μτ product" in CdZnTe single crystal materials also takes into account the technical level of CdZnTe single crystal materials, and is set to 1.0 × 10⁻⁶. -3 cm 2 The CdZnTe single crystal of the present invention has a range of 1.0 × 10⁻⁶ μτ products, which can be referred to as the "high μτ product". -3 cm 2The area of ​​the μτ product above / V should account for more than 50% of the total area of ​​the principal surface. The higher this area ratio, the better, but depending on the situation, it can also be more than 60% or 70%.

[0027] The CdZnTe single crystal of this invention is made by replacing a portion of the Cd in CdTe with Zn from the same group (Group II) element. The substitution ratio, i.e., the atomic ratio of Zn in Group II elements represented by the following formula (1), can be in the range of 2.0 at% to 10.0 at%. By setting this range, it can be adjusted to be suitable for applications in useful components utilizing the photoelectric effect, especially detectors for radiation such as X-rays. The lower limit of the atomic ratio of Zn in Group II elements can be set to 3.0 at% or 4.0 at%, and the upper limit can be set to 7.0 at% or 6.0 at%. Furthermore, in the CdZnTe single crystal material of this invention, the concentration (number of atoms per unit area) of Cd and Zn can be analyzed by near-infrared (NIR) spectroscopy to calculate the atomic ratio of Zn in Group II elements.

[0028] {Zn / (Cd+Zn)}×100 (at%) (1) (Cd and Zn are the number of Cd and Zn atoms in a CdZnTe single crystal, respectively) The orientation of the main surface of a CdZnTe single crystal can be set according to the application or desired characteristics. In this invention, for example, it can be set as a {111} surface. By setting it to this orientation, in addition to being used as a general-purpose semiconductor substrate, it can also exhibit better characteristics in applications such as radiation detectors.

[0029] The CdZnTe single crystal of the present invention is obtained by having an area of ​​at least 100 mm². 2 The above, and the mobility lifetime product (μτ product) becomes 1.0 × 10 -3 cm 2 The region above / V is specific to the structure and characteristics of more than 50% of the main surface area, and its manufacturing method is not particularly limited as long as the aforementioned characteristics can be obtained. However, when manufacturing CdZnTe single crystals by means of a manufacturing method including specific heat treatment after CdZnTe crystal growth, the conditions of the heat treatment will greatly affect the μτ product of the CdZnTe single crystal. Therefore, it is better to properly control the conditions for effectively obtaining the CdZnTe single crystal of the present invention.

[0030] Specifically, after growing a CdZnTe ingot using a specific method, the ingot is directly subjected to heat treatment for CdZnTe crystallization. The heat treatment temperature is controlled to be above 800°C and below 1000°C, and the difference between the maximum and minimum temperatures in the region between the upper and lower ends of the CdZnTe ingot is controlled to be within 20°C. This effectively manufactures the CdZnTe single crystal of the present invention. The heat treatment temperature can be above 900°C.

[0031] Heat treatment after CdZnTe crystal growth is a known technique that has been practiced for some time. Generally, not limited to CdZnTe, strict temperature control is required during the growth of bulk crystalline ingots because even slight temperature changes are sensitive to the crystallinity and other properties of the grown crystals. However, it is generally believed that heat treatment after crystal growth is mostly aimed at improving crystallization defects or homogenizing impurity distribution. As long as it is performed within a temperature range that promotes the excitation of desired lattice vibrations or the diffusion of impurities without causing dissociation of crystal constituent elements or dissolution of the crystalline material, there is no problem.

[0032] In practice, it is generally considered impractical to maintain strict temperature control of the entire crystal ingot, with a temperature difference of several degrees to about 20 degrees Celsius, in the high-temperature range of 800–1000°C, under conditions such as heat treatment after crystal ingot growth. This is impractical considering factors such as the maintenance or investment in equipment required for such heat treatment, crystal manufacturing efficiency, and manufacturing costs. However, through repeated detailed analysis and research, the inventors discovered that even slight differences in the heat treatment conditions after crystal ingot growth can significantly affect the proportion of high μτ product regions in the single crystals obtained during the manufacturing of CdZnTe single crystals.

[0033] Although the detailed reasons why maintaining the temperature difference of the entire crystal ingot below 20°C during heat treatment can increase the proportion of high μτ product regions may not be fully understood, it is believed that one of the main reasons is that heat treatment under conditions of small temperature difference within the crystal can significantly improve the degree of improvement of the unevenness of element concentration locally generated within the crystal due to the precipitation of Te or segregation of Zn during the growth of CdZnTe crystals.

[0034] The growth of CdZnTe crystal ingots subjected to the aforementioned heat treatment can be carried out by any known method, such as the vertical gradient solidification (VGF) method, the vertical Brinell (VB) method, or the Cabo dauphine method. Among these methods, after the crystal ingot has grown, the VGF method is preferred as a method for efficiently utilizing the aforementioned heat treatment. Furthermore, regarding the specific growth method and conditions for CdZnTe crystal ingots using the VGF method, it is sufficient to use methods and means disclosed in Patent Documents 1 and 2 that are known and which are also followed in the present invention.

[0035] Furthermore, the aforementioned heat treatment can be carried out directly and continuously in the furnace where the CdZnTe ingot was grown after the ingot has grown. This minimizes the temperature change experienced by the ingot from the time the CdZnTe ingot grows until the start of the heat treatment, and also allows for a short and efficient single crystal manufacturing process.

[0036] Furthermore, in addition to the above, various technical modifications or additions can be made within the scope of solving the technical problems of this invention. Even with such modifications or additions, as long as the essential aspects within the scope of the claims are satisfied, they are naturally included within the technical scope of this invention.

[0037] Example The present invention will now be described in detail based on embodiments, comparative examples, etc. The specific examples described below are merely for the purpose of facilitating understanding of the technical content of the present invention, and the technical scope of the present invention is not limited to these specific examples.

[0038] (Example 1) First, CdZnTe ingots were grown using the VGF method. (Using...) Figure 1 The crystallization growth furnace shown contains a pBN crucible with an inner diameter of 5 inches (approximately 127 mm) placed in the crystallization growth section of a quartz ampoule, which serves as the growth container, to achieve a composition of Cd in atomic ratios. 0.95 Zn 0.05 The raw material is filled using the method of Te (Zn from Group II elements: 5 at%). Furthermore, after adding Cd for gas vapor pressure control to the storage section of the quartz ampoule, the quartz ampoule is vacuum-sealed. This quartz ampoule is installed inside the crystallization growth furnace, and the settings are as follows... Figure 1 The temperature gradient shown is used for furnace heating. While the raw material is molten in the crucible, the temperature gradient of the melt is maintained at 1.3℃ / cm, and the temperature of the crucible is slowly reduced, thereby growing CdZnTe crystals from the surface of the melt downwards.

[0039] After the bottom of the crucible reaches the solidification temperature, the CdZnTe ingot is then heat-treated inside the furnace where it grows. The temperature distribution along the crystal growth direction near the ingot in the furnace at this time is as follows: Figure 2 The solid line indicates that the maximum temperature in the region containing the crystalline ingot is 969.0℃, and the minimum temperature is 952.7℃, with a difference of 16.3℃. After heat treatment for 1200 minutes under this condition, the crystalline ingot was slowly cooled to room temperature at a cooling rate of 50℃ / hr, and the obtained CdZnTe crystalline ingot was removed.

[0040] After circumferential grinding of the obtained crystalline ingot, a circular wafer shape is cut out from the {111} plane perpendicular to the crystal growth direction, and the surface is ground and polished. Then, a wafer composed only of single crystal is formed from the portion of the crystal that has not undergone polycrystalline transformation. The wafer surface of this single crystal wafer is the same as the main surface of the CdZnTe single crystal of the present invention. The CdZnTe single crystal wafer in this state is cut to obtain multiple CdZnTe single crystal substrates.

[0041] For each of the multiple CdZnTe single-crystal substrates obtained above, the μτ product was measured in the following manner. Specifically, as disclosed in Patent Document 2, the radiation spectrum of cobalt (Co-57) was measured when different bias voltages (250 V, 500 V, 700 V, and 900 V) were applied in two stages using a radiation detector composed of each sample. Furthermore, the peak positions of each spectrum were determined, and the μτ product of electrons was calculated using a specific formula. As a result, the μτ product was calculated relative to the total surface area of ​​the multiple CdZnTe single-crystal substrates, which is 1485 mm². 2 The product of μ and τ is 1.0 × 10 -3 cm 2 The total surface area of ​​the substrate with a voltage of / V or higher is 810 mm. 2 That is, in the CdZnTe single-crystal wafer before crystal cutting, the product of μτ in 54.5% of the area region on the wafer surface becomes 1.0 × 10⁻⁶. -3 cm 2 / V or higher. Furthermore, the average concentration of Zn among group II elements in this wafer is 5.2 at%.

[0042] (Example 2) CdZnTe ingots were grown under the same conditions as in Example 1, and then heat-treated in the same furnace. In Example 2, the maximum temperature during heat treatment in the region containing the ingot was 968.8°C, and the minimum temperature was 952.0°C, a difference of 16.8°C. After heat treatment for 1200 minutes under these conditions, the ingots were slowly cooled to room temperature and removed, as in Example 1. Circular wafers were cut from the {111} facet, and their surfaces were ground and polished. Then, wafers consisting only of single crystals were fabricated from the polycrystalline portion of the wafer-shaped crystals.

[0043] Similarly to Example 1, the CdZnTe single-crystal wafer was cut to obtain multiple CdZnTe single-crystal substrates, and the μτ product of each CdZnTe single-crystal substrate was measured. As a result, in Example 2, the total area relative to the surface of the multiple CdZnTe single-crystal substrates was 496 mm². 2 The product of μ and τ is 1.0 × 10 -3 cm 2 The total surface area of ​​the substrate with a voltage of / V or higher is 336 mm. 2 That is, in the CdZnTe single-crystal wafer before crystal cutting, the product of μτ in 67.7% of the area region on the wafer surface becomes 1.0 × 10⁻⁶. -3 cm 2 / V or higher. Furthermore, the average concentration of Zn among group II elements in this wafer is 5.1 at%.

[0044] (Example 3) CdZnTe ingots were grown under the same conditions as in Example 1, and then heat-treated in the same furnace. In Example 3, the maximum temperature during heat treatment in the region containing the ingot was 961.0°C, and the minimum temperature was 946.0°C, a difference of 15.0°C. After heat treatment for 1200 minutes under these conditions, the ingots were slowly cooled to room temperature and removed, as in Example 1. Circular wafers were cut from the {111} facet, and their surfaces were ground and polished. Then, wafers consisting only of single crystals were fabricated from the polycrystalline portion of the wafer-shaped crystals.

[0045] Similarly to Example 1, the CdZnTe single-crystal wafer was cut to obtain multiple CdZnTe single-crystal substrates, and the μτ product of each CdZnTe single-crystal substrate was measured. As a result, in Example 3, the total area relative to the surface of the multiple CdZnTe single-crystal substrates was 112 mm². 2 The product of μ and τ is 1.0 × 10 -3 cm 2 The total surface area of ​​the substrate with a voltage of / V or higher is 80 mm. 2That is, in the CdZnTe single-crystal wafer before crystal cutting, the product of μτ in 71.4% of the area region on the wafer surface becomes 1.0 × 10⁻⁶. -3 cm 2 / V or higher. Furthermore, the average concentration of Zn among group II elements in this wafer is 5.2 at%.

[0046] (Comparative Example 1) CdZnTe ingots were grown under the same conditions as in Example 1, and then heat-treated in the same furnace. The temperature distribution along the crystal growth direction near the ingot in the furnace at this time is as follows: Figure 2 The dotted line indicates the location. In Comparative Example 1, the maximum temperature during heat treatment in the region containing the crystallized ingot was 999.8°C, and the minimum temperature was 943.2°C, a difference of 56.6°C. For comparison, the temperature distribution along the crystal growth direction near the crystallized ingot in Comparative Example 1 is also shown. Figure 2 After undergoing heat treatment for 1200 minutes in this state, the crystal ingot was slowly cooled to room temperature and removed, as in Example 1. A circular wafer shape was cut from the {111} facet, and the surface was ground and polished. Then, a wafer composed solely of single crystals was fabricated from the portion of the crystal that did not undergo polycrystalline transformation.

[0047] Similarly to Example 1, the CdZnTe single-crystal wafer was cut to obtain multiple CdZnTe single-crystal substrates, and the μτ product of each CdZnTe single-crystal substrate was measured. As a result, in Comparative Example 1, the total area relative to the surface of the multiple CdZnTe single-crystal substrates was 256 mm². 2 The product of μ and τ is 1.0 × 10 -3 cm 2 The total surface area of ​​the substrate with a voltage of / V or higher is 16 mm. 2 That is, in the CdZnTe single crystal wafer of Comparative Example 1 before crystal cutting, only 6.3% of the wafer surface area can achieve 1.0 × 10⁻⁶. -3 cm 2 The product of μτ above / V. Furthermore, the average concentration of Zn among Group II elements in this wafer is 5.2 at%.

[0048] These results are summarized in Table 1.

[0049] Table 1 Industrial availability This invention provides a CdZnTe single crystal that achieves a high μτ product over a wide area, and an efficient method for its manufacturing. The technology of this invention makes a significant contribution to improving product performance, manufacturing efficiency, and yield in various semiconductor devices manufactured using the characteristics of CdZnTe single crystals. These include a wide range of semiconductor industries, such as X-ray detectors (which utilize the photoelectric effect to achieve high charge collection efficiency through a high μτ product), infrared detectors, solar cells, electro-optic modulators, and optical components.

[0050] Symbol explanation: 100: CdZnTe crystallization growth furnace 101: pBN crucible 102: Raw material molten liquid (growth crystallization) 103: Cd for storage 110: Growth container (quartz ampoule) 111: Crystal growth section 112: Storage Department 130: Heating device.

Claims

1. A single crystal of zinc cadmium telluride (CdZnTe) having an area of ​​100 mm² 2 The above, and the mobility lifetime product (μτ product) becomes 1.0 × 10 -3 cm 2 The area above / V represents more than 70% of the main surface of the entire structure. The proportion of Zn in Group II elements is 2.0 at% to 10.0 at%, and The orientation of the main face mentioned above is face {111}.

2. A method for manufacturing zinc cadmium telluride single crystals, as described in claim 1, comprising: Growth of zinc cadmium telluride crystal ingots, The aforementioned grown zinc cadmium telluride crystal ingots were directly heat-treated in ingot form, and Single crystals are cut from the heat-treated zinc cadmium telluride ingot using a main face with a specific orientation. The temperature of the heat treatment is above 946°C and below 969°C, and the difference between the maximum and minimum temperatures in the region between the upper and lower ends of the crystallized ingot is within 16.3°C.

3. The method for manufacturing zinc cadmium telluride single crystals according to claim 2, wherein, The difference between the maximum and minimum temperatures in the region between the upper and lower ends of the crystallized ingot is within 15.0℃.

4. The method for manufacturing zinc cadmium telluride single crystals according to claim 2 or 3, wherein, The above-mentioned zinc cadmium telluride crystal ingot growth method is the vertical gradient solidification (VGF) method.

5. The method for manufacturing zinc cadmium telluride single crystals according to claim 2 or 3, wherein, After the above-mentioned single crystal ingot is grown, the above-mentioned zinc cadmium telluride crystal ingot is continuously heat-treated in the furnace in which the above-mentioned single crystal ingot is grown.

Images