Why the substrate material matters
When an edge-emitting laser diode runs at high current, the junction temperature rises rapidly unless heat is removed efficiently. A submount placed between the device and the metal carrier package acts as a thermal spreader. The material you choose determines how fast heat flows, how well the thermal expansion matches your device, and what metallization options are available.
ALN (aluminum nitride) and SiC (silicon carbide) are both high-performance choices that outperform standard alumina by a wide margin. But they are optimized for different application profiles.
Thermal conductivity
| Material | Thermal conductivity | vs. Alumina |
|---|---|---|
| ALN (aluminum nitride) | 170–210 W/m·K | 6–8× better |
| SiC (silicon carbide) | 350–400 W/m·K | 13–15× better |
| Al₂O₃ (alumina, 99.6%) | 26–30 W/m·K | baseline |
SiC has roughly twice the thermal conductivity of ALN, making it the right choice when you are pushing the limits of power density — multi-watt CW laser bars, high-power lidar emitters, and GaN power devices. For most single-mode and low-to-mid-power laser diode applications, ALN is sufficient and typically less expensive.
CTE matching — the other critical parameter
Coefficient of thermal expansion (CTE) mismatch between the submount and the device die generates stress during temperature cycling. Over thousands of cycles this causes delamination, cracking, or shift in optical alignment.
| Material | CTE (ppm/°C) | Best device match |
|---|---|---|
| ALN | 4.3–4.6 | GaAs (5.7), InP (4.5), Si (2.6) — excellent for InP lasers |
| SiC | 3.7–4.3 | GaN (5.6), Si (2.6) — good for GaN and power devices |
| GaAs device | 5.7 | — |
| InP device | 4.5 | — |
| Si device | 2.6 | — |
ALN at 4.3–4.6 ppm/°C is an excellent match for InP-based laser diodes (4.5 ppm/°C), which are the dominant active material in telecom and datacom optical modules. SiC at 3.7–4.3 ppm/°C is better suited for GaN power devices and has a closer match to silicon than ALN does.
Metallization options
Both materials support standard thin-film metallization stacks:
- Ti/Pt/Au — universal choice for wire bonding and die attach
- Ti/Ni/Au — higher Au thickness for solder die attach
- Au/Sn 80/20 (3–5 µm) — predeposited for laser diode assembly, eliminates solder preform handling
Au/Sn predeposited on the edge pads is particularly valuable for edge-emitting laser diode assembly. It eliminates the need to handle small solder preforms and avoids solder rollup in the critical submount edge areas. FerraLink offers edge gap geometries down to 5 µm for the most demanding alignment requirements.
Decision guide: ALN or SiC?
Choose ALN when:
- InP or GaAs laser diodes (CTE match)
- Single-mode telecom or datacom modules
- Power density up to ~50–100 W/cm²
- Cost is a factor — ALN is less expensive than SiC
- Standard TO header or butterfly package assembly
Choose SiC when:
- GaN or Si power devices
- High-power CW laser bars (>100 W/cm²)
- Lidar emitters with extreme thermal load
- Best possible thermal performance regardless of cost
- Power electronics modules (EV, industrial)
FerraLink pricing vs. US and Japanese suppliers
FerraLink sources ALN and SiC submounts directly from ISO9001 and IATF16949 certified manufacturers, eliminating the domestic manufacturing premium charged by US suppliers and the import markup added by Japanese distributors. Typical pricing is 1/3 of equivalent US supplier quotes and 1/2 of Japanese supplier quotes — with the same material certs and quality documentation.
Standard part numbers (FL-ALN-005, FL-ALN-010, FL-ALN-015, FL-SiC-010, FL-SiC-020) are available as $25 individual samples or as a $250 testing box. Custom sizes, thicknesses, and metallization stacks are available on request.