# Why can't a reverse biased diode conduct by majority carrier injection (UPDATED)?

I know that the question "why can't a reverse biased diode conduct" has been asked before (here and here), but I'm asking it from a bit different perspective.

Why can't we inject electrons into the conduction band of the p-type material, which then would fall down the junction into the conduction band of the n-type material, and vice versa, inject holes into the valence band of the n-type material, which would climb up the junction to reach the valence band of the p-type material? This would even be energetically favorable, since this way both carriers would move through the reverse biased built-in potential which is their natural movement direction, not like in the case of forward bias, where they have to move by diffusion.

UPDATE: I have been thinking a lot about this, but still couldn't understand, so I'm updating the question. I meant injecting charge from the electrodes (suppose that they are ideal, non-rectifying), not injecting (e.g. photo-) generated charge through the depletion region. I have drawn a figure, which shows the charge carrier concentrations and energy levels in the diode in case of a reverse bias. To be honest, in case of the majority carrier concentrations in a region, I just simply took the $n_i^2/\text{minority carrier concentration}$, which is not exactly true near to the junction, due to the Fermi levels being separated (so this might be the trick). The "$0$" index denotes equilibrium concentrations, when there is no junction formed, there is just the p- and the n-type material, separate from eachother. The way I see it, both the concentrations, and the electric field is such, that there could be current flowing. So my question remains, why can't be electrons injected from the (ideal!) contacts to the conduction band of the p-type material, and holes into the valence band of the n-type material, which would permit a (quite huge) reverse current.

• You mean like how a solar cell works (or a photodiode)? Or a surface barrier detector for charged particles? Yes, if you inject charge carriers through some (external) process into a depletion layer, they will move. – Jon Custer Apr 6 '16 at 17:33
• @JonCuster I didn't mean into the depletition layer, but into either of the semiconductors, from the battery. See my comment below L.Levrel's answer. – user3237992 Apr 7 '16 at 9:13
• OK, you might want to look in to the Gunn and/or Hecht equations. For example, in the solar cell case, the minority carrier in the electron-hole pair generated near to, but not in, the depletion layer can indeed diffuse to the depletion layer edge and then get swept in to the junction to generate current. – Jon Custer Apr 7 '16 at 12:46
• @JonCuster But can you tell me why it is not possible what I said in the comment? (Honestly, I'd like to avoid further equations, unless absolutely necessary.) – user3237992 Apr 7 '16 at 16:16
• Tip: Concerning editing see this meta post. – Qmechanic May 16 '16 at 13:27