Tracking and controlling ultrafast charge and energy flow in graphene-semiconductor heterostructures

Low-dimensional materials have left a mark on modern materials science, creating new opportunities for next-generation optoelectronic applications. Integrating disparate nanoscale building blocks into heterostructures offers the possibility of combining the advantageous features of individual components and exploring the properties arising from their interactions and atomic-scale proximity. The sensitization of graphene using semiconductors provides a highly promising platform for advancing optoelectronic applications through various hybrid systems. A critical aspect of achieving superior performance lies in understanding and controlling the fate of photogenerated charge carriers, including generation, transfer, separation, and recombination. Here, we review recent advances in understanding charge carrier dynamics in graphene-semiconductor heterostructures by ultrafast laser spectroscopies. First, we present a comprehensive overview of graphene-based heterostructures and their state-of-the-art optoelectronic applications. This is succeeded by an introduction to the theoretical frameworks that elucidate the fundamental principles and determinants influencing charge transfer and energy transfer-two critical interfacial processes that are vital for both fundamental research and device performance. We then outline recent efforts aimed at investigating ultrafast charge/energy flow in graphene-semiconductor heterostructures, focusing on illustrating the trajectories, directions, and mechanisms of transfer and recombination processes. Subsequently, we discuss effective control knobs that allow fine-tuning of these processes. Finally, we address the challenges and prospects for further investigation in this field.