Enhancement of photoresponse in Bi2Se3/graphene heterostructures by effective electron-hole separation through internal band bending

Topological insulators (TIs) have been investigated as attractive candidates for the channels and contact metals of high-performance photodetectors over a broad spectral range. To achieve excellent photoresponse performances, several suggestions regarding material selection, various heterostructures, and proper device structure have been proposed. Here, we investigated the photoresponse of Bi2Se3/graphene heterostructures in lateral photodetectors. Graphene, with similar lattice symmetry, can improve the crystallinity of grown Bi2Se3 films, as well as induce large internal band bending with Bi2Se3, thereby causing electron-hole (e-h) separation. By comparing the photoresponses in vertical Bi2Se3 stack structures grown on various substrates, we conclude that the significantly improved photoresponse in the Bi2Se3/graphene stack structure results from graphene-induced internal band bending. Moreover, by investigating the thickness dependence of the Bi2Se3/graphene heterostructures on photoresponse, the maximum photoresponse is determined to be the result of an enhanced e-h separation caused by internal band bending and limiting of the optical penetration depth. As a well-matched stack structure based on band bending and the crystal growth system, TI/graphene heterostructures with stable and excellent photoresponse abilities can be considered as attractive candidates to attain outstanding performances for optoelectronic applications.