Critical Role of Dopant Location for P-Doped Si Nanocrystals

The doping of phosphorus (P) provides an additional means to control the optical properties of silicon nanocrystals (Si NCs). The P-doping-induced changes in the optical properties of Si NCs, however, have not been consistently understood. On the basis of first-principles calculations, we explain the P-doping-induced infrared absorption of Si NCs and the effect of P-doping on the light emission from Si NCs. The explanations are enabled by the investigation of the locations of P in Si NCs, including a variety of locations at the surface of Si NCs. We show that the light emission from Si NCs critically depends on the location of P. Transitions involving P-doping-induced defect energy levels lead to the infrared absorption of Si NCs.