Accurate electro-optical characterization of high power density GaAs-based Laser diodes for screening strategies improvement

摘要

In this study, we report on a methodology based on reverse and forward current-voltage curves (Ⅰ-Ⅴ) and on Degree of Polarization (DoP) of electroluminescence measurements on 980 nm laser diodes chip-on-submount (CoS) for the improvement of screening tests. Current-voltage curves are performed at reverse bias up to breakdown voltage (Vbr) using both a high current accuracy (＜ 1 pA) and high voltage resolution (＜ 10 mV) at different submount-temperatures (20-50℃). The DoP of luminescence of such devices, related to strains in materials and effect of shear strain on the birefringence, is calculated from the simultaneous measurement of TE (L_(te)) and TM (L_(tm)) polarized light emissions. We observe that application of high reverse voltages occasionally produces significant micro-plasma (MP) pre-breakdown on reverse I-V characteristics as recently observed in InGaN/GaN LEDs and assumed to be a response of electrically active defects. Comparisons between breakdown voltages and number of MP, and changes of leakage current at low forward voltage (＜ 0.1 V) are considered. DoP measurements are also analyzed versus temperature. Finally the usefulness of these measurements for effective screening of devices is discussed.