I am experimenting with optically controlling BJTs. In my current project, I take transistors in metal cans and use a diamond saw lubricated with isopropyl alcohol to slice the top off. This generates very little debris and presumably doesn't scratch the silicon die inside.
After the cutting, I hooked up the transistor and was able to use light to control the transistor, and it seemed to operate the same as any ordinary phototransistor.
So here's my question: Will a transistor opened in this manner degrade over time? Are there problems associated with exposing it to air or dust? Or is it passivated or otherwise protected in a robust way?