Current Drift in pn Junctions

In some pn junctions, the current through a pn junction degrades exponentially with time. This effect is only noticeable at a low bias with tens of mA. The current drift happens because at this low bias, much of the current (in these certain diodes) is carried by surface recombination current. Over time, heat caused by the current flow causes oxidation of the surface of the active layer, thus reducing the empty sites at the surface and decreasing surface recombination current.