Thermal Management Challenges of High-Power Semiconductor Lasers and the Core Competitiveness of SiC Heat Sinks

High-power semiconductor lasers are widely used in industrial manufacturing, defense and military systems, biomedical applications, and scientific research. However, thermal management after device packaging has long been a critical bottleneck limiting their performance and reliability. Addressing this challenge hinges on the integration of heat-sink materials that offer superior heat dissipation capability and greater thermal stability under high-temperature operating conditions.

Core Competitiveness of Silicon Carbide (SiC) Heat Sinks

As the primary carrier of heat transfer, the performance of a heat sink directly determines the effectiveness of thermal management. The technical limitations of conventional solutions are becoming increasingly evident.

Metal heat sinks such as copper and aluminum are cost-effective but suffer from severe thermal expansion mismatch with common laser gain media such as GaN and InP, leading to concentrated thermal stress during temperature cycling. Aluminum nitride (AlN) ceramic heat sinks face challenges in controlling interfacial thermal resistance and maintaining structural stability, making them inadequate for kilowatt-level and above laser systems. Although chemical vapor deposition (CVD) diamond offers exceptional thermal conductivity, its prohibitively high fabrication cost and the ongoing difficulty in defect control for wafers larger than 3 inches limit its large-scale adoption.

In contrast, silicon carbide (SiC) heat sinks demonstrate clear comprehensive advantages.

1. Excellent Thermal Parameter Matching and Balanced Performance

SiC exhibits outstanding thermal performance balance. Its room-temperature thermal conductivity reaches 360–490 W·m⁻¹·K⁻¹, comparable to copper (397 W·m⁻¹·K⁻¹) and 1.66–2.26 times higher than that of aluminum (217 W·m⁻¹·K⁻¹), providing a solid foundation for efficient heat dissipation in high-power laser systems.

In terms of thermal expansion, SiC has a coefficient of 3.8–4.3 × 10⁻⁶ K⁻¹, closely matching GaN (3.17 × 10⁻⁶ K⁻¹) and InP (4.6 × 10⁻⁶ K⁻¹). This is significantly better than copper (16.5 × 10⁻⁶ K⁻¹) and aluminum (23.1 × 10⁻⁶ K⁻¹), effectively reducing interfacial thermal stress.

Compared with CVD diamond and AlN, the performance balance of SiC is even more pronounced. While CVD diamond features ultra-high thermal conductivity (~2000 W·m⁻¹·K⁻¹), its thermal expansion coefficient (1.0 × 10⁻⁶ K⁻¹) is severely mismatched with gain media such as Yb:YAG (6.8 × 10⁻⁶ K⁻¹). AlN offers a thermal expansion coefficient close to that of SiC (4.5 × 10⁻⁶ K⁻¹) but its thermal conductivity (180 W·m⁻¹·K⁻¹) is only about 45% of that of 4H-SiC, significantly limiting heat dissipation efficiency.

This unique combination of high thermal conductivity and excellent thermal expansion matching positions SiC as an optimal material with well-balanced thermal performance.

2. Strong Environmental Adaptability and High Operational Stability

SiC exhibits excellent oxidation resistance, radiation tolerance, and a Mohs hardness of up to 9.2. These properties enable it to withstand harsh operating environments involving high temperatures and intense radiation, supporting long-term stable operation of high-power laser systems and reducing maintenance costs.

By comparison, traditional metal heat sinks have clear shortcomings. Copper is prone to oxidation and corrosion, causing interfacial thermal resistance to increase over time and resulting in gradual degradation of heat dissipation performance. Aluminum, on the other hand, suffers from insufficient mechanical strength, with a Brinell hardness of only 20–35 HB, making it susceptible to deformation during assembly and operation.

3. Excellent Bonding Compatibility and Low Engineering Barriers

SiC is highly compatible with various bonding technologies, including metallized bonding, direct bonding, and eutectic bonding, enabling low-interfacial-thermal-resistance integration with compound semiconductors such as GaN and InP. This versatility provides ample design flexibility for heterogeneous integration solutions.

Moreover, the maturity of SiC bonding processes significantly lowers the barriers to engineering implementation, ensures compatibility with existing semiconductor manufacturing lines, and accelerates the transition from laboratory research to practical applications.

Owing to these advantages, SiC has become the preferred heat-sink material for high-power lasers and is widely used in semiconductor lasers (LDs), thin-disk lasers (TDLs), and vertical-cavity surface-emitting lasers (VCSELs).

Preparation Methods of SiC Heat Sinks and Application-Specific Adaptation

As a wide-bandgap semiconductor, SiC exists in multiple polytypes, including 3C-SiC, 4H-SiC, and 6H-SiC. Differences in preparation methods and material properties provide a basis for application-specific heat-sink optimization.

(1) Physical Vapor Transport (PVT)

Prepared at temperatures above 2000 °C, producing 4H-SiC and 6H-SiC with thermal conductivity of 300–490 W·m⁻¹·K⁻¹. These materials offer high thermal conductivity and mechanical strength, making them suitable for high-power laser devices with stringent structural stability requirements.

(2) Liquid Phase Epitaxy (LPE)

Conducted at relatively moderate temperatures (1450–1700 °C), enabling precise control over 3C-SiC and 4H-SiC polytypes. Thermal conductivity ranges from 320–450 W·m⁻¹·K⁻¹. LPE-SiC is particularly advantageous in high-end laser devices requiring high power, long lifetime, and strict crystal consistency.

(3) Chemical Vapor Deposition (CVD)

Produces high-purity 4H-SiC and 6H-SiC with thermal conductivity of 350–500 W·m⁻¹·K⁻¹. High thermal conductivity ensures efficient heat extraction, while excellent dimensional stability prevents deformation after heat removal. The combination of these attributes is essential for long-term stable operation under extreme conditions, making CVD-SiC a preferred solution that balances performance and reliability.

Summary

With its superior thermal parameter matching, strong environmental adaptability, and excellent process compatibility, SiC has emerged as an ideal heat-sink material for high-power laser systems. In heterogeneous bonded devices, leveraging the differentiated thermal expansion characteristics of various SiC polytypes and crystal orientations enables optimal interfacial matching and maximized heat dissipation performance.