Non-invasive optical assessment of packaging-induced defects in high-power laser diodes

Packaging of laser chips or bars is a crucial technological process during production of high power laser devices. The main goal of this process is to mount the semiconductor chip with high electrical and thermal conductivity on a heat sink while preserving the quality of the semiconductor laser chip. Nevertheless, the defect concentration in the optically active layer of the semiconductor chip might be influenced by the packaging technology. Therefore non-invasive measurements of packaged laser diodes are required. Photocurrent (PC) measurements turned out to be a good tool for characterizing the defect status of the chip in dependence on the packaging technology. We show that QW-laser diodes emitting at 808 nm and mounted p-side down can be affected by defects (traps), that are introduced with different thermal processing (soldering). The defects found are spatial located within the QW-region. Direct interaction between quantum-confined carriers and trap levels is demonstrated by PC bleaching experiment. We show that steady-state non-equilibrium carrier population of the QW-states, that is about proportional to the photocurrent, is governed by defects.