Q.Non-stoichiometric cuprous oxide, $Cu_2O$ can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than 2:1. Can you account for the fact that this substance is a p-type semiconductor?

If the copper-to-oxygen ratio is a little below $2:1$, some $Cu^+$ ions are absent from their lattice sites. To restore electrical neutrality, an equal amount of $Cu^+$ is oxidised to $Cu^{2+}$. These $Cu^{2+}$ centres behave as positive holes through which conduction occurs, s …

Step 1 – Interpret the sub-stoichiometry.

In perfect $Cu_2O$ the ratio $Cu:O = 2:1$ with all copper as $Cu^+$. Since the actual ratio is slightly less than 2:1, some $Cu^+$ ions are missing from their lattice positions (cation vacancies).

Step 2 – Restore electrical neutrality.

Each missing $Cu^+$ removes one positive charge. To keep the crystal neutral, an equivalent number of remaining $Cu^+$ ions lose an electron and become $Cu^{2+}$:

Step 3 – Origin of p-type conduction. …

Explain the metal-deficiency defect: fewer $Cu^+$ than stoichiometric $\Rightarrow$ some $Cu^+$ oxidised to $Cu^{2+}$ for neutrality $\ …

• Saying extra oxygen is added rather than copper being deficient.
• Claiming conduction is by electrons (it is by positive holes for p-type). …