Thermal management has a crucial impact on the performance of high power semiconductor lasers. Poor heat dissipation can lead to an increase in junction temperature, a decline in output power, and a decrease in conversion efficiency, thereby affecting the operational stability and lifetime. Heat sinks play a crucial role in the heat dissipation of semiconductor lasers. In recent years, as the output power of semiconductor lasers continues to rise, higher demands are placed on their heat dissipation performance. As a third-generation semiconductor material, silicon carbide (SiC) has a theoretical thermal conductivity of 490 W/(m·K), much higher than that of aluminum nitride (AlN) ceramics [270 W/(m·K)]. It is regarded as an ideal material for manufacturing heat sinks for semiconductor laser packaging. Therefore, packaging semiconductor lasers with single crystal SiC heat sinks is an effective solution to improve the heat dissipation issues of high power semiconductor lasers.

In this study, we first design and fabricate single crystal SiC heat sinks with and without copper coated. After the heat sinks are fabricated, we select 640 nm and 915 nm chips from the same batch, package them with SiC heat sinks and compare them with laser diodes (LDs) packaged with standardized commercial AlN heat sinks. The 640 nm laser chip adopts the TO9 packaging form, and the 915 nm laser chip adopts the chip on submount (COS) packaging form. Finally, performance tests including power-current-voltage(P-I-V) and output wavelength are conducted on the 640 nm LD and the 915 nm LD. Based on the test results, the thermal resistance of the lasers is calculated.

Through comparative experimental results, the maximum output power of the 640 nm LD packaged with the single crystal SiC heat sink is 4.8 W, which is higher than 4.3 W of the LD packaged with the AlN heat sink. Its threshold current and electro-optical conversion efficiency are also superior to those of the LD packaged with the AlN heat sink (Fig. 3). As the operating temperature increases, the output power of the former packaged with the single crystal SiC heat sink decreases by 0.78 W, while that of the latter packaged with the AlN heat sink decreases by 1.3 W (Fig. 4). In the wavelength test, the temperature drift coefficient of the LD packaged with the single crystal SiC heat sink is 0.24 nm/℃, while that of the LD packaged with the AlN heat sink is 0.261 nm/℃ [Fig. 5(a)]. As the operating current rises from 1 A to 2 A, the wavelength of the former increases by 1.23 nm, while the wavelength variation of the latter is 1.56 nm [Fig. 5(b)]. Through calculation, the thermal resistance of the LD packaged with the single crystal SiC heat sink is 3.32 K/W, which is lower than 5.45 K/W of the LD packaged with the AlN heat sink. In the catastrophic optical damage (COD) test, the LD packaged with the single crystal SiC heat sink achieves an output power of 8.7 W at 8 A, while the LD packaged with the AlN heat sink fails at 6.8 A (Fig. 6). The maximum output power of the 915 nm LD packaged with the single crystal SiC heat sink with copper coated is 1.9 W, higher than that of the LD packaged with the AlN heat sink with copper coated. The maximum electro-optical conversion efficiency is 64.9% at 30 A, which is higher than 62.1% of the latter (Fig. 7). In the wavelength test under different temperatures, it can be concluded that the wavelength drift coefficient of the 915 nm LD packaged with the single crystal SiC heat sink with copper coated is 0.358 nm/℃, which is smaller than 0.397 nm/℃ of the LD packaged with the AlN heat sink with copper coated (Fig. 8).

In this paper, single crystal SiC heat sinks with and without copper coated are developed based on single crystal SiC, and they are used to package and test the 640 nm and 915 nm laser chips. Through comparison, the 640 nm LD packaged with the single crystal SiC heat sink has an output power of 4.8 W and an electro-optical conversion efficiency of 42.7%, while the 915 nm laser packaged with the single crystal SiC heat sink with copper coated has an output power of 54.5 W and an electro-optical conversion efficiency of 64.9%. All performance indicators are superior to those of LDs packaged with AlN heat sinks. As the temperature increases, the wavelength drift of LDs packaged with single crystal SiC heat sinks is smaller. Therefore, packaging laser chips with single crystal SiC heat sinks is an effective method to improve the output power and the thermal management problems of semiconductor lasers.