HVPE Technology: The Key Growth Method for High-Quality GaN Single-Crystal Substrates

With the increasing demand for high-performance gallium nitride (GaN) materials in power electronics, RF devices, and optoelectronics, the efficient production of large-size, high-quality, low-defect GaN single crystals has become a focal point in the industry. Among various growth techniques, Hydride Vapor Phase Epitaxy (HVPE) stands out as the leading method for GaN substrate fabrication due to its high growth rate, low defect density, and cost-effectiveness. This article provides an in-depth overview of the HVPE process, including its principles, growth mechanism, technological advantages, and its crucial role in the fabrication of freestanding GaN substrates.

1. HVPE Process Principles: Vapor Transport and Epitaxial Growth

HVPE is a vapor transport-based epitaxial growth technique that involves two primary chemical reactions:

（1）Gallium chloride (GaCl) formation (high-temperature zone, ~850°C):

                                    Ga(s)+HCl(g)→GaCl(g)

Metallic gallium (Ga) reacts with hydrogen chloride (HCl) at high temperatures to form gaseous GaCl.

（2）GaN deposition (growth zone, ~1000°C):

                                    GaCl(g)+NH3(g)→GaN(s)+HCl(g)+H2(g)

GaCl reacts with ammonia (NH₃) in a high-temperature environment, forming solid GaN while the byproducts HCl and H₂ are exhausted.

Precise control of the GaCl/NH₃ ratio, temperature distribution, and vapor transport dynamics is crucial for achieving high-quality, uniform GaN crystal growth.

2. HVPE System Configuration and Growth Environment

A typical HVPE system consists of a horizontal or vertical reactor comprising the following components:

1. Gallium source zone: Where metallic gallium reacts with HCl to form GaCl vapor.

2. Transport zone: GaCl is carried by hydrogen (H₂) or nitrogen (N₂) to the growth chamber.

3. Growth zone: GaCl and NH₃ react to deposit GaN on the substrate.

4. Exhaust system: Removes byproducts (HCl and H₂) to maintain a stable reaction environment.

   
   

To ensure high-quality GaN deposition, the process requires high-purity precursor gases and precise temperature control throughout the system.

3. HVPE Growth Process

(1) Substrate Preparation

HVPE epitaxial growth requires a suitable substrate, typically:

• Sapphire (Al₂O₃): Cost-effective and widely used in LED manufacturing.

• Silicon Carbide (SiC): Ideal for high-power electronic devices such as GaN HEMTs.

• Freestanding GaN: Offers the highest crystalline quality but at a higher production cost.

Prior to growth, the substrate undergoes cleaning and annealing (~1000°C) to remove surface oxides and improve adhesion.

(2) Low-Temperature Buffer Layer Deposition

A thin GaN buffer layer is deposited at ~500°C to mitigate strain and improve epitaxial quality.

(3) High-Rate Epitaxial Growth

Once the system stabilizes, the temperature is increased to ~1000°C, allowing GaCl and NH₃ to react and form GaN at a growth rate exceeding 100 µm/h.

• Optimizing the V/III ratio (NH₃/GaCl) reduces nitrogen vacancies and improves crystal quality.

• Controlling gas flow ensures uniform deposition and minimizes surface roughness.

• Maintaining a well-defined temperature gradient lowers stress and dislocation density.

(4) Thick GaN Film Growth and Freestanding GaN Substrate Fabrication

HVPE enables the growth of 300-500 µm thick GaN layers, which can be separated from the original substrate via laser lift-off (LLO) or chemical etching, resulting in a freestanding GaN substrate.

4. Advantages of HVPE Technology

✅ High Growth Rate: HVPE achieves rates exceeding 100 µm/h, significantly surpassing MOCVD (~3 µm/h), making it ideal for thick film growth and large-scale production.

✅ Low Defect Density: GaN grown via HVPE exhibits defect densities as low as 10⁶ - 10⁷ cm⁻², far superior to MOCVD-grown layers (10⁸ - 10⁹ cm⁻²).

✅ Large-Area Substrate Production: HVPE allows the fabrication of 2-inch to 4-inch, and even 6-inch GaN substrates, advancing high-power applications.

✅ Cost-Effectiveness: HVPE relies on cost-efficient raw materials such as HCl, NH₃, and Ga, making it more economical compared to MBE or HPHT methods.

5. HVPE in Freestanding GaN Substrate Fabrication

HVPE is the dominant technology for producing large-size, high-quality GaN substrates, following this process:

1️⃣ Grow a thick GaN layer (300-500 µm) on sapphire or SiC substrates.

2️⃣ Use laser lift-off (LLO) or chemical etching to remove the original substrate, yielding a freestanding GaN wafer.

3️⃣ Polish and chemically treat the GaN surface to achieve the required substrate quality.

Freestanding GaN substrates are essential for high-power electronics (GaN HEMTs), RF devices (GaN MMICs), deep-UV LEDs, and laser diodes (LDs) due to their superior material properties.

6. Conclusion: HVPE as the Preferred Technology for High-Quality GaN Substrates

HVPE has established itself as the industry standard for GaN substrate production due to its high growth rate, low defect density, and scalability for large wafer sizes.

Our GaN Substrates Are Manufactured Using HVPE Technology

We utilize HVPE technology to produce high-quality GaN substrates with the following key features:

✅ Exceptional crystal quality, suitable for high-end optoelectronic and power electronic applications.

✅ Available in 2-inch to 4-inch sizes to meet various industry requirements.

✅ Low defect density, ensuring high device reliability.

✅ Customizable thickness, surface finish, and doping types.

For more information or custom requirements, feel free to contact us!