Reliability of InP-based avalanche photodiodes for high bit-rate fiber-optic communication systems

We report on a study of the impact of mechanical stress on the electrical properties of InP-based avalanche photodiodes used in OC48 and OC192 10 Gb/s fiber-optic communication applications. The device structure under study consists of separate absorption, grading, charge and multiplication regions. A large population of devices, which were die bonded onto carriers using a range of epoxy and eutectic solder adhesives, has been subjected to accelerated life testing for >5000 h under high thermal and electrical overstress conditions. In addition, we have performed an analysis of the response of the current-voltage characteristics of the device to an external mechanical stress. The mechanical stress experiments give insight into variations in device performance that may arise if the die bonding process is not performed properly. Relaxation in device strain, due to thermally induced epoxy bond degradation, is shown to be a potential hazard, which can interfere with reliability assessment of the device. When these factors are controlled, the device lifetime exhibits the expected log-normal distribution, characterized by an exceptionally low wearout FIT rate.