Hello, I have a small question about the image included in this topic. The plot describes the situation where the semiconductor is n-doped. Shouldn’t n_h also be non-zero for the extrinsic region ? It is stated that N_D > N_A, but there should still be a number of holes excited from the acceptor band ? Thanks in advance for your response.
Hi,
In the extrinsic regime, we know that all of the carriers come from donors or acceptors.
- If we only have donors, then it is expected that we find no holes.
- If we have N_D>N_A then even if there are also acceptors these will be filled with electrons from the donors, leaving no holes as carriers. That is why in this regime we do not have N_D electrons, but N_D-N_A.
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