Non-stoichiometric cuprous oxide, Cu2O can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than 2:1.

When cuprous oxide is prepared in laboratory, the ratio of copper to the oxygen in the compound becomes slightly less that 2:1. This happens because some of the Cu+ ions are replaced by Cu2+ ions. In this process, one Cu2+ ion is replaced by two Cu+ ions. As two Cu+ ions are replaced by one Cu 2+, this creates a defect because of vacant space, i.e. positive hole. Because of the creation of holes due to this defect, this compound conducts electricity through these positive holes. As semiconductors which are formed by electron deficient impurities are called the p – type semiconductors; thus cuprous oxides so formed in laboratory are p – type semiconductors.