Description

Consider two metal-semiconductor junctions as follow:

1. Metal | n-type semiconductor

2. Metal | p-type semiconductor

In both junctions, let us have this condition

Metal's work function < semiconductor's work function

such that the semiconductor in both junction case (1 and 2) experiences "downward" band bending at the interface.

The difference is

for case 1: it is ohmic contact

for case 2: it is rectifying contact

Downward band bending is favorable for electron transfer since electron "roll" downhill.

Now consider that these junctions are illuminated such that we now have comparable number of electrons in CB and holes in VB of the semiconductor (because charge generation due to illumination is much much greater than the number of minority carriers).

Conclusion

Based on my description, we can conclude two things

1. Both junctions experience "downward" band bending which favor electron transfer

2. Under illumination, the number of "electrons" at both junctions are the same

Based on this conclusion, it seems there are no different properties in both junctions

Question

which junctions (1 or 2) will favor the electron transfer from semiconductor to metal? if both of them favor electron transfer from semiconductor to metal, which one is better and why?