Carrier Transport Across a CdSxSe1–x Lateral Heterojunction Visualized by Ultrafast Microscopy

Charge and energy transport across semiconducting heterointerfaces plays a central role in optoelectronic devices such as solar cells and light-emitting diodes. However, the understanding of these transport processes has been hindered by the lack of experimental tools that can provide detailed information in both spatial and temporal domains. Here, we demonstrate the use of ultrafast transient absorption microscopy to image charge dynamics and transport across semiconducting heterojunctions, using type I CdSxSe1–x lateral heterostructures as a model system. These experiments visualize carrier diffusion in the individual materials and the transmission of carriers through the interface. The carrier diffusion constant in the CdSxSe1–x alloys is measured to be around 1 cm2 s–1. Energy transfers from the higher bandgap to the lower bandgap material in ∼1 ns and the transmission of carriers across the interface is efficient with a probability of ∼80%. These results showcase the capability of transient absorption microscopy in visualizing interfacial charge transport in nanostructured heterojunctions.