We often use diode detectors at microamp currents, and the question arises as to the type of diode best suited to sensitive detectors.
Setting aside zero bias Schottky diodes which are a topic in themselves, the choice is typically between commonly available germanium, silicon and Schottky signal diodes.
Above is a plot of the I,V characteristic of four common signal diodes at currents up to 1mA. It can be seen that at currents below 600µA, the forward voltage drop of the humble 1N34A germanium diode is lower than the others. The 1N270 is an alternative if you really need its higher breakdown voltage. Both of these diodes are reasonably easy to obtain, and cheap at that.
- Duffy, O. May 2011. Measuring common mode current. https://owenduffy.net/module/icm/index.htm (accessed 22/10/16).