  Diodes made of heterostructures of the 2D material graphene and conventional
3D materials are reviewed in this manuscript. Several applications in high
frequency electronics and optoelectronics are highlighted. In particular,
advantages of metal-insulator-graphene (MIG) diodes over conventional
metal-insulator-metal diodes are discussed with respect to relevant
figures-of-merit. The MIG concept is extended to 1D diodes. Several
experimentally implemented radio frequency circuit applications with MIG diodes
as active elements are presented. Furthermore, graphene-silicon Schottky diodes
as well as MIG diodes are reviewed in terms of their potential for
photodetection. Here, graphene-based diodes have the potential to outperform
conventional photodetectors in several key figures-of-merit, such as overall
responsivity or dark current levels. Obviously, advantages in some areas may
come at the cost of disadvantages in others, so that 2D/3D diodes need to be
tailored in application-specific ways.
