Temperature-humidity-bias-behavior and acceleration model for InP planar PIN photodiodes

The reliability of InP planar PIN photodiodes in humid ambients has been studied. The dependence of the degradation rate in temperature, humidity and bias was determined by aging devices at temperatures between 50 and 150°C, humidities between 50 and 85% RH, and biases between 2 and 25 V. Failure occurred as a result of a sudden increased dark current. This increase in dark current had little affect on the device responsivity. At all aging conditions the failure distributions were well represented by a lognormal distribution in time with a dispersion of less than 0.3. From these data, an acceleration factor (AF) was developed and is given by AF=exp(E/kT)exp[A(RH)²]exp[B(V)] where E=-0.42 eV, A=-4.6×10^-4, and B=-6.7×10^-2/V. Extensive failure mode analysis was done on more then 500 failed devices. Based on this, a failure mechanism was proposed. The model requires ingress of moisture to the InP surface. The moisture is reduced at the p-contact region of the device region, giving off hydrogen. Under negative bias In and P react with the hydrogen to form gaseous IH and PH ₃. This lead to the semiconductor erosion. The erosion continues until device failure occurs. The worst case concentrate of PH ₃ which if created would produce less than 0.1 ppb PH₃ per cm³ of air. Thus it is not a fire or health hazard. Finally, we present reliability prediction for nonhermetic PIN´s encapsulated in an optically clear silicone based polymer. We estimate a 20 year hazard rate of less than 100 FIT´s for devices operating at an ambient of 45°C/50% RH. For comparison, the hermetic counterparts of similar design have a 20 year hazard rate of less than 10 FIT´s