GaN-based P-type ohmic contact structure based on silicon nitride and magnesium nitride composite structure and preparation method of GaN-based P-type ohmic contact structure

Abstract

The invention discloses a GaN-based P-type ohmic contact structure based on a silicon nitride and magnesium nitride composite structure and a preparation method of the GaN-based P-type ohmic contact structure, and the ohmic contact structure is arranged on a P-type GaN layer and comprises a SiN / MgN composite structure. The SiN / MgN composite structure is formed by stacking SiN layers and MgN layers of 1 to 3 cycles; wherein the thickness of the SiN layer is 1-2 nm, and the thickness of the MgN layer is 2-4 nm; the Si doping concentration of the SiN layer is 1 * 10 < 17 >-6 * 10 < 17 > cm <-3 >, and the Mg doping concentration of the MgN layer is 5 * 10 < 19 >-3 * 10 < 21 > cm <-3 >. The preparation method provided by the invention comprises the step of growing the composite structure under the conditions of 750-900 DEG C and 200-500 Torr. The high work function of MgN, the energy band bending of the SiN / PGaN interface and the tunneling effect formed by Mg diffusion are utilized to synergistically reduce the P-type ohmic contact resistance, and the beneficial effects of reducing the voltage of the device and improving the brightness and the lighting effect are achieved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to a GaN-based P-type ohmic contact structure based on a silicon nitride and magnesium nitride composite structure and its preparation method. Background Technology

[0002] Achieving low-resistance, high-stability ohmic contacts in GaN-based devices (such as LEDs, lasers, and power electronic devices) has been a long-standing technical challenge and one of the key bottlenecks for industrialization.

[0003] The difficulty in establishing ohmic contacts in p-type GaN stems from the intrinsic physical properties of the material. Firstly, p-type GaN typically uses magnesium (Mg) as a dopant. However, the ionization energy of Mg acceptors in GaN is very high, around 150-200 meV. This results in only about 1% of Mg atoms being able to ionize and generate holes at room temperature, making the effective hole concentration far lower than the Mg doping concentration, typically only around 10. 17 cm -3 The extremely low hole concentration makes it extremely difficult to form ohmic contacts with low resistivity.

[0004] Secondly, according to semiconductor physics theory, to form an ohmic contact in a P-type semiconductor, ideally, the work function of the contact metal should be greater than that of the semiconductor to reduce the height of the Schottky barrier for hole injection. However, for P-type GaN, there are almost no metal materials in reality that have a sufficiently high work function while also being compatible with the manufacturing process and maintaining long-term stability.

[0005] In summary, existing P-type GaN contact layer designs (such as direct metal deposition on a P-GaN:Mg layer) often result in high ohmic contact resistance, leading to increased overall device resistance and consequently higher driving voltage, thus affecting the device's luminous efficiency and electro-optical conversion efficiency. Therefore, developing a novel ohmic contact structure and method that can significantly reduce the contact resistance of P-type GaN is crucial for improving the performance of GaN-based devices. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a novel GaN-based P-type ohmic contact structure and its preparation method, aiming to solve the problems of high ohmic contact resistance, high device voltage and low luminous efficiency caused by the low hole concentration and lack of high work function metal in P-type GaN.

[0007] To achieve the above objectives, the present invention provides a GaN-based P-type ohmic contact structure disposed on a P-type GaN layer, characterized in that it includes a SiN / MgN composite structure disposed on the P-type GaN layer.

[0008] As a preferred embodiment, the SiN / MgN composite structure is a SiN / MgN superlattice structure.

[0009] Furthermore, the superlattice structure comprises one to three cycles of SiN and MgN layers.

[0010] Furthermore, the thickness of the SiN layer in the superlattice structure is 1 nm to 2 nm, and the thickness of the MgN layer is 2 nm to 4 nm.

[0011] Furthermore, the total thickness of the superlattice structure is 3 nm to 18 nm.

[0012] Furthermore, the SiN layer is a silicon-doped SiN layer with a Si doping concentration of 1×10⁻⁶. 17 -6×10 17 cm -3 .

[0013] Furthermore, the MgN layer is a Mg-doped MgN layer with a Mg doping concentration of 5 × 10⁻⁶. 19 -3×10 21 cm -3 .

[0014] In a specific application scenario, the structure further includes, sequentially disposed below the SiN / MgN composite structure: the P-type GaN layer; the P-type electron blocking layer (EBL); the multiple quantum well (MQW) active layer; the N-type GaN (nGAN) layer; the undoped GaN (uGAN) layer; the buffer layer; and the substrate.

[0015] To achieve the above objectives, the present invention also provides a method for preparing a GaN-based p-type ohmic contact, used to prepare the structure described in any of the above claims, characterized in that it includes the step of forming a SiN / MgN composite structure on a p-type GaN layer by epitaxial growth.

[0016] As a preferred embodiment, the epitaxial growth process parameters include: a growth temperature controlled at 750°C to 900°C; and a growth pressure controlled at 200 Torr to 500 Torr.

[0017] Furthermore, the step of forming the SiN / MgN composite structure includes: alternating growth of SiN and MgN layers to form a superlattice structure; wherein, by adjusting the flow rates of Mg source, ammonia (NH3) and silane (SiH4), the composition of the SiN and MgN layers is precisely controlled.

[0018] Furthermore, at the interface of the superlattice, gradient growth or interrupted growth methods are employed to reduce interface defects.

[0019] The core of this invention lies in replacing the traditional P-type ohmic contact with a specially designed SiN / MgN composite structure. Through the synergistic effect of multiple physical mechanisms, the problem of P-type GaN ohmic contacts is fundamentally solved. Synergistic effect reduces contact resistance: The SiN / MgN composite structure of the present invention does not achieve ohmic contact through a single mechanism, but rather through the synergistic effect of at least three mechanisms, which greatly reduces contact resistance.

[0020] Mechanism 1: MgN itself is reported as a p-type semiconductor with a theoretical work function as high as 5.0-5.3 eV. This high work function value makes it very suitable for forming low-barrier ohmic contacts with p-type GaN, which is difficult to achieve with conventional metals.

[0021] Mechanism 2: The SiN layer acts as an interface layer, exhibiting a dipole effect at its interface with the P-type GaN layer, and the presence of a fixed positive charge within the SiN layer (this charge density can be determined by the Si doping concentration of 1×10⁻⁶). 17 -6×10 17 cm -3 (Through regulation), these factors collectively cause the energy bands on the P-type GaN surface to bend downwards. This band bending directly reduces the barrier height for holes to be injected from P-GaN into the contact layer.

[0022] Mechanism 3: After subsequent device processing, the MgN layer (with an extremely high Mg doping concentration, reaching 5 × 10⁻⁶) 19 -3×10 21 cm -3 Some Mg atoms from the SiN (which can serve as a Mg source) diffuse through the ultrathin (1-2 nm) SiN layer. This forms an extremely thin, heavily doped region on the surface of the p-type GaN. According to quantum mechanics, this heavily doped region makes the depletion region extremely narrow, allowing holes to cross the potential barrier with little or no thermal emission, instead becoming the dominant current transport mechanism through tunneling. Tunneling significantly improves current transport efficiency and fundamentally reduces contact resistance.

[0023] Confirmed Data Improvement: The beneficial effects of this invention have been confirmed by experimental data. Compared with comparative examples using existing contact layer designs, GaN-based devices employing the SiN / MgN composite structure of this invention exhibit improved electrical and optical performance: voltage decreased by 0.02V, brightness increased by 0.5mW, and luminous efficacy improved by 0.7%. The voltage reduction directly confirms the reduction in ohmic contact resistance. The improvement in brightness and luminous efficacy indicates that the improvement in electrical performance (low resistance, low power consumption) has successfully translated into improved optical performance.

[0024] This comprehensively confirms the design effectiveness of the present invention and solves the core problem of efficiency limitation caused by high contact resistance in the prior art. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the extensional structure of existing technology.

[0026] Figure 2 This is a schematic diagram of the extensional structure of an embodiment applying the structure of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example

[0029] Reference Figure 2 This embodiment provides a GaN-based P-type ohmic contact structure, which is applied in a complete GaN-based LED epitaxial structure. The epitaxial structure is stacked as follows: On a sapphire substrate 100, the following epitaxial growth techniques, such as metal-organic chemical vapor deposition (MOCVD), are used to grow sequentially: Buffer layer 200, such as low-temperature AlN or GaN; Undoped GaN (uGAN) layer 300; N-type GaN (nGAN) layer 400, Si doped; Multiple quantum well (MQW) active layer 500, InGaN / GaN quantum well; Low-temperature p-type GaN (LT-PGaN) layer 600; P-type AlGaN (P-AlGAN) 700, used as an electron blocking layer (EBL). P-type GaN (P-GAN) layer 800, Mg doped.

[0030] A SiN / MgN superlattice PP ohmic contact layer 900 of the present invention is grown on the p-type GaN (P-GAN) layer, with the following parameters: Total number of cycles: 2 cycles.

[0031] Single-period structure: SiN layer: 1.5 nm thick.

[0032] MgN layer: 3.0 nm thick.

[0033] Total thickness: (1.5 + 3.0) nm / cycle × 2 cycles = 9 nm.

[0034] Doping concentration: SiN layer: Si doping concentration is 5×10 17 cm -3 .

[0035] MgN layer: Mg doping concentration is 1×10 20 cm -3 .

[0036] The fabrication method of the above structure involves the growth process of the SiN / MgN superlattice PP ohmic contact layer: After the P-GAN layer is grown, the process parameters are adjusted in the MOCVD reaction chamber to begin growing the SiN / MgN superlattice.

[0037] Growth conditions: Growth temperature: controlled at 800 ℃.

[0038] Pressure: Controlled at 300 Torr.

[0039] Growth process: Composition control: The flow rates of Cp2Mg (Mg source), NH3 (N source), and SiH4 (Si source and dopant for SiN) are precisely controlled using MOCVD equipment.

[0040] Period 1: 1. Introduce SiH4 and NH3 to grow a 1.5 nm SiN layer.

[0041] 2. Interface processing: The interrupted growth method is adopted, and the gas source is briefly turned off or switched to ensure the interface is flat and reduce interface defects.

[0042] 3. Introduce Mg source and NH3 to grow a 3.0 nm MgN layer.

[0043] Period 2: 1. Interface processing: The interrupted growth method is used again.

[0044] 2. Introduce SiH4 and NH3 to grow a 1.5 nm SiN layer.

[0045] 3. Interface handling: interrupt growth.

[0046] 4. Introduce Mg source and NH3 to grow a 3.0 nm MgN layer.

[0047] After growth is complete, annealing is performed to promote the diffusion of Mg and realize the tunneling mechanism described in the invention.

[0048] To verify the beneficial effects of the present invention, a comparative example was prepared.

[0049] Comparative example: using Figure 1 The existing structure shown is an ohmic contact using a conventional metal electrode deposited on the P-GAN layer.

[0050] Embodiment of the present invention: using Figure 2 The structure of the present invention shown is the structure with a SiN / MgN superlattice PP ohmic contact layer described in the embodiments.

[0051] Under the same test conditions, the electrical and optical performance of the two types of devices were tested, and the comparative data are shown in Table 1.

[0052] Table 1: Performance Comparison of Embodiments and Comparative Examples of the Invention Comparison Items Comparative Example Embodiments of the present invention change Voltage (V) 3.13 3.11 -0.02 Brightness (mW) 274.9 275.4 +0.5 ESD yield 97.80% 97.83% +0.03% Lighting effect (%) 87.83 88.55 +0.73 As shown in Table 1, the voltage in this embodiment of the invention decreased by 0.02V, which directly confirms that the SiN / MgN composite structure effectively reduces the ohmic contact resistance through its unique synergistic mechanism. The decrease in total device resistance due to the reduced contact resistance results in a lower driving voltage at the same current.

[0053] Meanwhile, the brightness increased by 0.5mW and the luminous efficacy improved by 0.73%, indicating that the improvement in electrical performance successfully translated into an improvement in optical performance, solving the core problem of efficiency limitation caused by high resistance in the prior art. The synergistic improvement in data (electrical and optical) strongly confirms the effectiveness and advancement of the technical solution of this invention.

[0054] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A GaN-based p-type ohmic contact structure based on a silicon nitride and magnesium nitride composite structure, disposed on a p-type GaN layer, characterized in that, include: A SiN / MgN composite structure disposed on the p-type GaN layer.

2. The structure according to claim 1, characterized in that, The SiN / MgN composite structure is a SiN / MgN superlattice structure.

3. The structure according to claim 2, characterized in that, The superlattice structure comprises one to three cycles of SiN and MgN layers.

4. The structure according to claim 2 or 3, characterized in that, The thickness of the SiN layer in the superlattice structure is 1 nm to 2 nm, and the thickness of the MgN layer is 2 nm to 4 nm.

5. The structure according to claim 4, characterized in that, The total thickness of the superlattice structure is 3 nm to 18 nm.

6. The structure according to any one of claims 1 to 5, characterized in that, The SiN layer is a silicon-doped SiN layer with a Si doping concentration of 1×10⁻⁶. 17 -6×10 17 cm -3 .

7. The structure according to any one of claims 1 to 6, characterized in that, The MgN layer is a magnesium-doped MgN layer with a Mg doping concentration of 5 × 10⁻⁶. 19 -3×10 21 cm -3 .

8. The structure according to claim 1, characterized in that, The structure further includes, sequentially disposed below the SiN / MgN composite structure: The P-type GaN layer; P-type electron blocking layer; Multi-quantum-well active layer; N-type GaN layer; Undoped GaN layer; Buffer layer; and Substrate.

9. A method for preparing a GaN-based p-type ohmic contact, used to prepare the structure as described in any one of claims 1 to 8, characterized in that, include: The step of forming a SiN / MgN composite structure on a P-type GaN layer by epitaxial growth.

10. The method according to claim 9, characterized in that, The epitaxial growth process parameters include: The growth temperature was controlled between 750℃ and 900℃; and Growth stress was controlled at 200 Torr to 500 Torr.

11. The method according to claim 9 or 10, characterized in that, The steps for forming the SiN / MgN composite structure include: Alternating SiN and MgN layers are grown to form a superlattice structure; The composition of the SiN and MgN layers is precisely controlled by adjusting the flow rates of the Mg source, NH3, and SiH4.

12. The method according to claim 11, characterized in that, At the interface of the superlattice, gradient growth or interrupted growth methods are used to reduce interface defects.

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