PbSe nanocrystals remain intrinsic after surface adsorption of hydrazine

Recent experiments have shown a dramatic increase in the conductivity of PbSe nanocrystalline films after hydrazine treatment, suggesting that hydrazine may create free carriers in PbSe nanocrystals. Here, we study the effect of hydrazine adsorption on the electronic structure of PbSe nanocrystals using density functional theory. The physisorption of the intact hydrazine molecule and its dissociative chemisorption on different surfaces of PbSe are considered. Despite experimental indications of the n-type doping by hydrazine in PbSe, no theoretical evidence of the effect is found. Instead, PbSe is predicted to remain an intrinsic semiconductor after surface doping by hydrazine, and become a p-type semiconductor after doping by the hydrazine fragments. We attribute the discrepancy between experiment and theory to indirect effects, such as self-doping by excess surface atoms due to selective surface etching.