  There has been a rapidly growing interest in optoelectronic properties of
graphene and associated structures. Despite the general belief on absence of
spontaneous emission in graphene, which is normally attributed to its unique
ultrafast carrier momentum relaxation mechanisms, there exist a few recent
evidences of strong optical gain and spontaneous light emission from mono-layer
graphene, supported by observations of dominant role of out-of-plane excitons
in polycyclic aromatic hydrocarbons. In this article, we develop a novel
concept of light emission and optical gain from simple vertical
graphene/dielectric tunnel junctions. It is theoretically shown that the
possible optical gain or emission spectrum will be easily tunable by the
applied voltage. We present details of quantum mechanical calculations and
perform an exact analysis of field-assisted tunneling using transfer matrices
combined with expansion on Airy's functions.
