AIN mirror coating for high-power (AlGa)As laser diodes

A method of high power (AlGa)As laser mirrors passivation with thin AIN layers deposited by low temperature reactive sputtering is presented. In SQW-SCH laser diodes (LDs) with high optical confinement the optical power densities at the mirrors are very high, leading at some power level to so-called catastrophic optical damage (COD) of the mirrors (and lasers). Thus the COD level limits the LD’s optical output and to improve it, mirrors are usually protected with dielectric coatings, such as SiO 2 , Si 3 N 4 and Al 2 O 3 layers. Here, the AIN layers are proposed as a LD mirror coatings because of their unique features including high smoothness and thermal conductivity (3.19 Wcm -1 K -1 ) which is close to that of copper (4.01 Wcm -1 K -1 ). Moreover thermal expansion coefficient of AIN matches well coefficient of GaAs. Single AIN layers (approx. λ/4 thick) have been deposited as front, low reflectivity LD coatings and for the rear, high reflectivity mirrors the AIN-Si λ/4 layer stacks (4 pairs) have been used. LDs with such coatings exhibit twofold external quantum efficiency and good stability during CW life test.