A metallization scheme for junction-down bonding of high-power semiconductor lasers

High-power semiconductor lasers have found increasing applications in industrial, military, commercial, and consumer products. The thermal management of high-power lasers is critical since the junction temperature rise resulting from large heat fluxes strongly affects the device characteristics, such as wavelength, kink power, threshold current and efficiency, and reliability. The epitaxial-side metallization structure has significant impact on the thermal performance of a junction-down bonded high-power semiconductor laser. In this paper, the influence of the epitaxial-side metal (p-metal) on the thermal behavior of a junction-down mounted GaAs-based high-power single-mode laser is studied using finite-element analysis. It is shown that a metallization structure with thick Au layer can significantly reduce the thermal resistance by distributing the heat flow to wider area laterally, and the thermal resistance of a junction-down bonded laser with thick Au metallization is much less sensitive to the voiding in the die attachment solder interface than a laser with thin Au metallization. A metallization structure of Ti-Pt-thick Au-Ti-Cr-Au is designed and implemented, and the metallurgical stability of this metallization scheme is reported. It was found that, without a diffusion barrier, the thick Au layer in the epi-side metallization would be mostly consumed and form intermetallics with the Sn from the AuSn solder during soldering and thermal aging. The Ti-Pt-thick Au-Ti-Cr-Au metallization scheme prevents the diffusion of Sn into the thick Au layer and preserves the integrity of the metallization system. It is a promising candidate for junction-down bonding of high-power semiconductor lasers for improved thermal management and reliability