Aluminum Nitride (ALN) Submounts

Aluminum nitride (ALN) is the dominant submount material for single-mode and multimode laser diodes in telecom, datacom, and industrial applications. Its combination of high thermal conductivity, well-matched coefficient of thermal expansion (CTE), and high electrical insulation makes it uniquely suited for direct die attachment under a laser diode junction.

At 170–210 W/m·K, ALN removes heat from the laser junction 6–8 times faster than standard alumina. For a 200–500 mA CW single-mode DFB laser, this keeps junction temperature within operating limits and extends device lifetime significantly. For higher-power devices, ALN's thermal performance is often the difference between a module that meets spec and one that fails thermal qualification.

The CTE of ALN at 4.3–4.6 ppm/°C closely matches InP (4.5 ppm/°C) and GaAs (5.7 ppm/°C) — the two most common laser diode semiconductor materials. This close match minimizes mechanical stress during thermal cycling, preventing delamination and preserving optical alignment over thousands of power cycles.

ALN is polycrystalline — under SEM, individual grains and grain boundaries are clearly visible at fracture surfaces. Phonons scatter at each grain boundary, which is why bulk thermal conductivity (170–210 W/m·K) is lower than single-crystal SiC (350–400 W/m·K). For most InP/GaAs laser diode applications, ALN provides sufficient thermal margin at lower cost. When absolute thermal performance is critical — pulsed lidar, laser bars, GaN power — see our single-crystal SiC submounts.