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As phototransistors age, their responsivity to light decreases (a fixed amount of light generate less photocurrent). To simulate long-term aging of phototransistors in a short period of time, one can conduct accelerated lifetime testing by exposing the phototransistor to electrical stresses.

The most common electrical stress is subjecting the phototransistor to high voltage and current (Vce) so that it is forced to dissipate much more power than its rated power dissipation. It seems that this can change the behavior of the phototransistor in a way similar to long-term aging. (E.g. see Surridge, et al., 2002, "Accelerated Reliability Testing of InGaP/GaAs HBTs" here).

I am wondering whether subjecting an NPN type phototransistor to reverse voltage exceeding its reverse breakdown voltage (that is, high voltage at the emitter, with the collector grounded), can also simulate long-term aging.

I believe that high reverse voltage causes impact ionization, which degrades the junction. (Read this in ONSemiconductors - "Understanding Power Transistors Breakdown Parameters here). Experimentally, a sufficiently high reverse voltage will cause current to flow backwards from emitter to collector, cause the sensor to heat up, and quickly decrease responsivity to incident light (tested in Vishay Electronics' BPW96B and BPV11F NPN phototransistors).

Is this similar to the way a phototransistor's sensitivity to light would decrease over years of aging? What is the physical mechanism behind long-term aging of phototransistors, and how does it compare to that of high reverse voltage?

ach-agarwal
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    There should be literature out there already on doing what you want. The key phrase you want to search on is "accelerated life testing" together with LED. HALT/HASS (or HALT/HAS, I can't remember which) are the Mil-Speak acronyms. I suspect that for LEDs, you want elevated temperature and higher than normal currents -- semiconductors in general wear out due to atom migration, and that happens faster at elevated temperature. At least 20 years ago, the wear mechanism for LEDs was that aluminum atoms would migrate in the direction of the electron flux -- I don't think that's still so. – TimWescott Jan 01 '20 at 17:41
  • I think HASS = Highly Accelerated Stress Screening – SteveSh Jan 01 '20 at 18:23
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    Accellerated aging can be accomplished in many ways, semiconductors in general will age exponentially faster with temperature, so just keeping the temperature up close to or at the maximum operating temperature will make any semiconductor age much faster. However I think a more important question is not how to produce accelerated aging, but rather what do you want to compare your results to? It is easy to get a part to fail fast, but determining even just roughly how much equivalent aging the part has been subjected to is often impossible. So what is your purpose for doing life-time testing? – Vinzent Jan 01 '20 at 22:13
  • @Vinzent - I hadn't considered that... I intend to simulate a few years of aging that approaches, but does not exceed, the lifetime of the device that the component is part of. This would be 5-10 years of aging... but you're right that I have no idea how to simulate this kind of aging. – ach-agarwal Jan 02 '20 at 03:38
  • @TimWescott - thanks for the reply; I'll definitely try searching again with these terms. Also, just to clarify, it's the phototransistor that I want to age, not LEDs - but your answer is relevant nonetheless. Thanks! – ach-agarwal Jan 02 '20 at 03:40

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