A method for regulating defect and doping characteristics of wide bandgap semiconductor materials

Abstract

In order to overcome the problems that the existing wide band gap semiconductor material has a large number of spontaneous defects, it is difficult to obtain intrinsic semiconductor and it is difficult to realize reverse type doping, the application discloses a method which can controllably improve the formation energy of spontaneous defects and simultaneously reduce the formation energy of reverse type doping defects by applying voltage, realizes the preparation of intrinsic wide band gap semiconductor material and reverse type doping. The method comprises the following operation steps: during the growth of intrinsic wide band gap semiconductor material and reverse type doping process, a positive bias is applied to the wide band gap semiconductor material which spontaneously forms N type conduction, and a negative bias is applied to the wide band gap semiconductor material which spontaneously forms P type conduction. The application also discloses the application of the above method in the preparation of intrinsic zinc oxide and P type doped zinc oxide.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, specifically relating to a method and application for controlling the defects and doping characteristics of wide bandgap semiconductor materials. Background Technology

[0002] Wide bandgap semiconductors, such as gallium nitride (GaN), aluminum nitride (AlN), silicon carbide (SiC), zinc oxide (ZnO), and gallium oxide (Ga2O3), possess characteristics such as large bandgap, high breakdown voltage, strong radiation resistance, high thermal conductivity, and high electron mobility. These properties make them ideal for fabricating high-voltage, high-temperature, high-frequency, and high-power electronic devices, as well as visible and ultraviolet light-emitting and photodetector devices, offering broad application prospects. Unlike traditional semiconductor materials, most experimentally prepared wide bandgap semiconductors exhibit strong N-type or P-type conductivity due to numerous spontaneously formed defects, and it is difficult to achieve the opposite conductivity through traditional doping methods. Therefore, obtaining intrinsic semiconductors with low defect concentrations and achieving high-efficiency inversion doping are crucial for the further development of wide bandgap semiconductor devices.

[0003] Without effectively eliminating a large number of spontaneous defects, the efficiency of current inversion doping is significantly reduced: the inversion carrier concentration obtained at typical doping concentrations is extremely low; while heavy doping can increase the inversion carrier concentration, the mobility is extremely low due to the excessively high defect concentration. For example, in 2006, researchers at Solid State Scientific in the United States used a hydrothermal method to study the p-type doping characteristics in nitrogen-doped ZnO films, and found that when the nitrogen atom doping concentration reached 10... 18 cm -3 At that time, the activated P-type concentration was only 10. 12 cm -3 The hole mobility was as low as 11 cm. 2 / V∙s. The aforementioned difficulties make it difficult to realize homojunction devices based on these wide-bandgap semiconductor materials. Therefore, these wide-bandgap semiconductor devices that are difficult to invert-dopate usually need to be based on heterojunctions. However, due to the complex fabrication process of heterojunction devices and the lattice mismatch between different materials resulting in many defects at the interface, the price, performance and lifespan of the devices are severely affected.

[0004] The aforementioned problems with wide-bandgap semiconductor materials are essentially determined by the thermodynamic properties of crystal defects within the material. According to the thermodynamic definition, a general crystal point defect... (Right now A Element atoms occupy the crystal B The lattice location, and the defect carries a charge. q The defect formation energy is shown in Equation 1.

[0005] (1)

[0006] in, and These respectively indicate defects. The internal energy of crystalline materials and corresponding perfect crystalline materials. The Fermi level of the crystal. μ A and μ B Let A and B be the chemical potentials of elements A and B under relevant experimental conditions. More complex crystal defects can be considered as being composed of multiple point defects, and therefore follow similar thermodynamic laws as point defects. The formation energy of the defect... It is inversely proportional to the concentration c of the defect in the crystal, as shown in Formula 2.

[0007] (2)

[0008] in, This represents the number density of related defects that may form in the crystal. The formation energy of related defects, Boltzmann's constant, This is the absolute temperature at which defects form, typically the material growth temperature.

[0009] By using formulas (1) and (2) and the principle of electrical neutrality satisfied by the crystal material as a whole (i.e., the sum of the charges of all charged defects, electrons and holes in the crystal is zero), the Fermi level of the material can be determined in a self-consistent manner, thereby determining the doping type and conductivity of the material under various conditions, as shown in formula 3.

[0010] (3)

[0011] in, and These are semiconductor materials at the Fermi level. The carrier measurement temperature is The concentration of free electrons and holes at that time For defects The concentration. Summary of the Invention

[0012] To address the problems of numerous spontaneous defects in existing wide-bandgap semiconductors, making it difficult to obtain intrinsic semiconductors and achieve inversion doping, this invention provides a method and application for controlling the defects and doping characteristics of wide-bandgap semiconductor materials.

[0013] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0014] On the one hand, the present invention provides a method for controlling the defects and doping characteristics of wide bandgap semiconductor materials. In the process of preparing intrinsic wide bandgap semiconductor materials or inversion doping, a preparation bias voltage or a doping bias voltage is applied to the wide bandgap semiconductor material through electrodes.

[0015] If the wide bandgap semiconductor material spontaneously forms N-type conductivity, a positive bias is applied; if the wide bandgap semiconductor material spontaneously forms P-type conductivity, a negative bias is applied.

[0016] Optionally, the wide bandgap semiconductor material may be in the form of a single crystal, a thin film, or a nanostructure.

[0017] Optionally, the wide bandgap semiconductor material can be grown under a fabrication bias voltage applied to the electrodes via hydrothermal, melting, or molecular beam epitaxy methods.

[0018] Optionally, the preparation bias voltage is -10 to 10 volts.

[0019] Optionally, an external electrode is covered on one side of the wide bandgap semiconductor material, and a doping bias is applied to the wide bandgap semiconductor material through the external electrode, while an inversion doping treatment is performed on the other side.

[0020] Optionally, the doping bias voltage is -10 to 10 volts.

[0021] On the other hand, the present invention provides the application of the method described above in the preparation of intrinsic and p-type doped zinc oxide single crystals, thin films or nanostructures.

[0022] Optionally, a preparation bias voltage of 1 to 3 volts is applied to the zinc oxide formation region.

[0023] Optionally, a doping bias voltage of 1 to 3 volts is applied to the zinc oxide material, while simultaneously performing P-type element doping.

[0024] Optionally, the P-type doping element includes one or more elements selected from Li, Na, Ag, N, P, and As. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the device provided by the present invention for controlling the growth of intrinsic wide bandgap semiconductors by external voltage.

[0026] Figure 2 This is a schematic diagram of the device provided by the present invention that controls the inversion doping of a wide bandgap semiconductor by means of an external voltage.

[0027] Figure 3 This invention provides the defect formation energy and Fermi level of point defects and paired defects in a ZnO crystal when no external voltage is applied. EF This represents the Fermi level when undoped. E F 'The nitrogen doping concentration is 10 12 cm -3 (Fermi level at that time).

[0028] Figure 4 This invention provides the defect formation energy and Fermi level of point defects and paired defects in a ZnO crystal when an external voltage of 1.15 volts is applied. E F This represents the Fermi level when undoped. E F 'The nitrogen doping concentration is 10 12 cm -3 (Fermi level at that time). Detailed Implementation

[0029] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0030] In the description of this invention, a doping process opposite to spontaneous conductivity is referred to as inversion doping. The term "positive bias" refers to applying a voltage to the wide-bandgap semiconductor material to be controlled, placing it at a high potential. For example, in a DC power supply, the wide-bandgap semiconductor material can be connected to the positive terminal of the DC power supply. The term "negative bias" refers to applying a voltage to the wide-bandgap semiconductor material to be controlled, placing it at a low potential. For example, in a DC power supply, the wide-bandgap semiconductor material can be connected to the negative terminal of the DC power supply.

[0031] To address the problems of numerous spontaneous defects in existing wide-bandgap semiconductors, making it difficult to obtain intrinsic semiconductors and perform inversion doping, this invention discloses a method and application for controlling the defect and doping characteristics of wide-bandgap semiconductor materials by applying an external voltage. Specifically, this invention proposes to apply an external voltage... U Controllable control point defects The defect formation energy is shown in Equation 4.

[0032] (4)

[0033] As can be seen from the above formula, the external voltage U defects The formation energy can be applied to a size of qU Additional effects. For wide-bandgap semiconductors that exhibit N-type conductivity due to spontaneous defects (such as zinc oxide), the spontaneous defects are positively charged ( q (positive), therefore applying a positive bias voltage can makeqU A positive bias increases the formation energy of spontaneous defects and decreases their concentration. However, for inversion doping (i.e., P-type doping), since the dopant element is negatively charged in the crystal, the positive bias can decrease the formation energy of the inversion dopant element and increase its concentration. Similarly, a negative bias can decrease the concentration of spontaneous defects in spontaneous P-type wide-bandgap semiconductors while increasing the concentration of N-type dopant elements.

[0034] The key advantages of the above method include: (I) The effectiveness of this method does not depend on the atomic composition of spontaneous defects or the specific wide-bandgap semiconductor material. This is because all crystal defects that lead to N-type or P-type conductivity have positive or negative charges and are modulated in the same direction by the external voltage. (II) This method can controllably regulate the concentration of spontaneous defects and dopant elements by means of an external voltage while keeping other growth conditions constant. In contrast, the traditional method of changing the reactants (corresponding to changing the...) μ A and μ B They often face many problems when growth conditions deviate from ideal conditions.

[0035] Based on this, the present invention further proposes the following general technical solution for implementing the above method.

[0036] First, intrinsic wide-bandgap semiconductor materials are prepared by the following method. During the synthesis of wide-bandgap semiconductor materials, a fabrication bias voltage is applied to the region where the wide-bandgap semiconductor material is formed, as illustrated in the diagram below. Figure 1 As shown. If the spontaneous defects of the wide bandgap semiconductor material exhibit N-type conductivity, then the applied fabrication bias voltage is a positive bias voltage; if the spontaneous defects of the wide bandgap semiconductor material exhibit P-type conductivity, then the applied fabrication bias voltage is a negative bias voltage. The fabrication bias voltage is -10 to 10 volts; the specific value depends on the wide bandgap semiconductor material and the growth method. When the fabrication bias voltage is too high, it will result in too many defects, thereby reducing the carrier mobility.

[0037] Second, based on obtaining the intrinsic wide-bandgap semiconductor material, a doping bias is applied to the wide-bandgap semiconductor material, and inversion doping is performed simultaneously. A related schematic diagram is shown below. Figure 2 As shown. If the spontaneous defects of the wide bandgap semiconductor material exhibit N-type conductivity, the applied doping bias voltage is a positive bias voltage (with the same sign as the preparation bias voltage); if the spontaneous defects of the wide bandgap semiconductor material exhibit P-type conductivity, the applied doping bias voltage is a negative bias voltage (with the same sign as the preparation bias voltage). The doping bias voltage is -10 to 10 volts.

[0038] The present invention further proposes the following specific technical solutions for ZnO materials.

[0039] As a wide-bandgap semiconductor material with wide technological applications, ZnO typically exhibits strong N-type conductivity. However, its intrinsic semiconductor properties and high-quality P-type doping have not yet been achieved. To address these issues and further demonstrate the method in this invention, the inventors employ a first-principles calculation method based on density functional theory (using a combination of the HSE06 hybrid exchange correlation function and the Hubbard U method). Taking hydrothermal growth of ZnO single crystals as an example, (1) the defect formation energy and Fermi level of ZnO crystals without applied bias voltage were studied, explaining the spontaneous N-type conductivity observed under typical experimental conditions. (2) Subsequently, using nitrogen-doped ZnO materials as an example, the inventors verified through calculation that nitrogen doping is difficult to achieve P-type doping without bias voltage. (3) Finally, the inventors confirmed that positive bias voltage can effectively suppress spontaneous N-type defects, achieving intrinsic ZnO semiconductor properties, and achieving effective P-type conductivity through nitrogen doping.

[0040] The hydrothermal method is currently a major technique for growing bulk ZnO single crystals. This method dissolves ZnO raw material in supercritical water at approximately 370 °C. ZnO molecules in the liquid phase rise to the top of the chamber, ultimately growing ZnO single crystals. The partial pressure of water vapor within the chamber is approximately 1080 atmospheres. The inventors determined the chemical potential under equilibrium conditions through the chemical reaction H₂O(gas) ↔ H₂(gas) + 0.5O₂(gas). μ O and μ H and through μ Zn + μ O = μ ZnO The chemical potential was determined μ Zn Then, using first-principles calculations, 10 types of point defects (namely oxygen vacancy defects) were studied. V O Zinc vacancy defects V Zn Oxygen gap defect O i Oxygen vacancies between Zn-Zn bonds i(split) Zinc interstitial defects Zn i Hydrogen interstitial defects H i Oxygen substitution defect O Zn Zinc substitution defects in Zn O Hydrogen substitution defect H O With H Zn ), 10 types of paired defects formed by point defects (respectively) V O +Zn i, V O+ V Zn , V O + V O , V Zn + V Zn , V O +Zn O , V O +O Zn H i + V Zn H i +O Zn H i +O i , V Zn +2H) and two types of nitrogen-doped defects (namely, nitrogen interstitial defects N). i With nitrogen substitution defect N O ).

[0041] Figure 3 The formation energy of the aforementioned crystal defects and the self-consistent Fermi level before nitrogen doping are given in the absence of external voltage. Self-consistent Fermi level with nitrogen doping The results show that the Fermi level of ZnO single crystals directly prepared by the hydrothermal method is 1.14 eV above the intrinsic Fermi level, exhibiting typical N-type conductivity. In nitrogen-doped N-type defects... O Concentration of 10 12 cm -3 Under these conditions, the Fermi level without bias, located 0.39 eV above the intrinsic Fermi level, still exhibits typical N-type conductivity. Therefore, the P-type doping effect of nitrogen is completely compensated for by the spontaneous defects in ZnO. These results confirm numerous previous experimental findings: without bias, ZnO spontaneously forms N-type conductivity, and P-type doping of nitrogen is difficult to achieve. The inventors' calculations also show that the spontaneous defect H... i and H O This is the main reason why ZnO exhibits N-type conductivity in the hydrothermal process. Because the hydrothermal process cannot eliminate H atoms, and the H atoms within... O The defects are extremely stable, so it is difficult to achieve intrinsic semiconductor properties through subsequent processing such as annealing for N-type ZnO single crystals prepared by hydrothermal method.

[0042] Figure 4 The formation energies of various crystal defects and the self-consistent Fermi level before nitrogen doping are given when a positive bias of 1.15 V is applied. Self-consistent Fermi level with nitrogen doping The results show that when a forward bias of 1.15 V is applied to the ZnO crystal, the dominant N-type spontaneous defect H... i and H O The formation energy is significantly increased, and its concentration is drastically reduced. At this point, the Fermi level of ZnO is 1.7 eV, which is exactly in the middle of the band gap, thus making it an intrinsic semiconductor. Under this bias condition, when N... O Doping concentration of 10 12 cm -3 At this point, the Fermi level of ZnO is located 0.77 eV below the intrinsic Fermi level, thus exhibiting typical P-type conductivity. Comprehensive analysis reveals that a positive bias of approximately 1.15 V can effectively suppress spontaneous N-type defects in ZnO under typical hydrothermal growth conditions, achieving intrinsic semiconductor properties. Furthermore, increasing the concentration of P-type dopant in the crystal under subsequent nitrogen doping further enhances P-type conductivity.

[0043] The method for controlling the defects and doping characteristics of wide bandgap semiconductor materials according to the present invention will be described in detail below through specific embodiments.

[0044] Example 1

[0045] The intrinsic wide-bandgap semiconductor material is prepared by the following method:

[0046] Step one: During the synthesis of wide bandgap semiconductor materials using hydrothermal, melt, or molecular beam epitaxy methods, a preparation bias voltage is applied to the wide bandgap semiconductor material through a top electrode. The electrode must be able to form a low-resistance ohmic contact with the wide bandgap semiconductor. If the spontaneous defects of the wide bandgap semiconductor material exhibit N-type conductivity, the applied preparation bias voltage is positive; if the spontaneous defects of the wide bandgap semiconductor material exhibit P-type conductivity, the applied preparation bias voltage is negative.

[0047] Step two involves placing the wide-bandgap semiconductor material and external electrode structure obtained in step one into a doping apparatus. A doping bias is applied to the intrinsic wide-bandgap semiconductor material through the top electrode, and inversion doping is performed on the other side of the wide-bandgap semiconductor material. The doping method can be thermal diffusion or ion implantation. If the spontaneous defects of the wide-bandgap semiconductor material exhibit N-type conductivity, the applied doping bias is positive; if the spontaneous defects of the wide-bandgap semiconductor material exhibit P-type conductivity, the applied doping bias is negative. In some embodiments, the doping bias is -10 to 10 volts.

[0048] It should be noted that the preparation process of the intrinsic wide-bandgap semiconductor material and the doping process of the inversion dopant can be independent steps; in other embodiments, the doping of the inversion dopant can also be performed simultaneously during the preparation process of the wide-bandgap semiconductor material. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0049] The following Example 2 further illustrates the method of the present invention for controlling the defects and doping characteristics of ZnO materials.

[0050] Example 2

[0051] This embodiment illustrates the method and application of the present invention for controlling defects and doping characteristics of ZnO materials, including the following steps:

[0052] Step 1: After covering the mask with a suitable substrate material, place it into a metal electrode deposition device and deposit Au metal target on the substrate material in an inert gas environment to obtain the external electrode.

[0053] Step two involves using a hydrothermal reaction vessel to obtain supercritical water at 370 °C, achieving an internal pressure of approximately 1080 atmospheres. An external electrode is then used to apply a DC voltage of approximately 1.15 volts to the ZnO growth region to suppress the formation of spontaneous N-type defects in the ZnO crystal. Under these conditions of high temperature, high pressure, and external voltage, intrinsic ZnO semiconductor single crystals are synthesized via a hydrothermal method.

[0054] Step 3: Seal the ZnO intrinsic semiconductor single crystal and Au electrode structure prepared in Step 2 into a quartz glass tube. Apply a positive bias voltage of approximately 1.1 volts to the external electrode. Raise the temperature inside the tube to 400 °C, introduce nitrogen gas mixed with an inert protective gas, and then ionize the nitrogen gas through arc discharge. Continue the experiment until the P-type conductivity meets the requirements.

[0055] The above description is merely an embodiment of the present invention and is not intended to limit the present invention; any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0056] In different embodiments, other P-type doping elements besides nitrogen, such as one or more of Li, Na, Ag, N, As, and P, may also be selected.

[0057] Optionally, the ZnO material is selected from zinc oxide single crystals, zinc oxide thin films, or zinc oxide nanostructures.

[0058] In different embodiments, a doping bias voltage is applied to the ZnO material while simultaneously performing inversion doping treatment; the doping bias voltage is 1.1 to 3 volts. When the preparation bias voltage is too high, the introduced P-type defect density becomes excessive, which reduces hole mobility.

[0059] In summary, the inventors have disclosed a new concept, method, and implementation device for controlling the thermodynamic stability of charged defects in wide-bandgap semiconductors by utilizing an external voltage, thereby regulating spontaneous defects and dopant concentration. The effectiveness of this method has been demonstrated in the example of ZnO crystals.

Claims

1. A method for controlling the defects and doping characteristics of wide-bandgap semiconductor materials, characterized in that: The wide bandgap semiconductor material is ZnO material. It is grown by applying a preparation bias voltage to the zinc oxide generation region through hydrothermal method, melt method or molecular beam epitaxy. The wide bandgap semiconductor material is grown under the preparation bias voltage applied to the electrode. The preparation bias voltage is 1~3 volts. An external electrode is covered on one side of the wide bandgap semiconductor material, and a doping bias voltage is applied to the wide bandgap semiconductor material through the external electrode. Inversion doping is performed on the other side of the surface, and the doping bias voltage is 1 to 3 volts.

2. The method according to claim 1, characterized in that, The wide bandgap semiconductor material can be in the form of single crystal, thin film, or nanostructure.

3. The application of the method according to any one of claims 1 to 2 in the preparation of p-type doped zinc oxide single crystals, thin films or nanostructures.

4. The application according to claim 3, characterized in that, The doping elements include one or more of the following: Li, Na, Ag, N, P, and As.

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