The effect of bonding wires on longitudinal temperature profiles of laser diodes

The thermal effect of bonding wires in laser diodes is analyzed using the analytical temperature solution for a five-layer structure and an iteration technique. Finite element method is used to confirm the results. Due to the bonding wire, the longitudinal temperature profile of laser diodes exhibits significant reduction at the foot of the wire even with uniform longitudinal heat distribution. For lasers designed with uniform longitudinal current density, heat increases toward the laser facets because of nonradiative recombination of carriers through surface quantum states on the facets. This leads to local temperature concentration on and near the facets. The conduction of heat through the bonding wire at the top center of laser chips further enhances this temperature concentration. In use, the stripe electrode of laser diodes is at uniform voltage. Under this operation condition, the current density would increase in the higher temperature regions due to bandgap decrease, causing higher heat flux. And consequently even higher temperature. Accordingly, the location of bonding wire and the shape of stripe electrode require careful consideration in the design phase to achieve uniform longitudinal temperature profile.