  Reverse-biased graphene (Gr)/semiconductor Schottky diodes exhibit much
enhanced sensitivity for gas sensing. However, carrier transport across the
junctions is not fully understood yet. Here, Gr/SiC, Gr/GaAs and Gr/Si Schottky
junctions under reverse-bias are investigated by temperature-dependent
current-voltage measurements. A reduction in barrier height with increasing
reverse-bias is observed for all junctions, suggesting electric-field enhanced
thermionic emission. Further analysis of the field dependence of the reverse
current reveals that while carrier transport in Gr/SiC Schottky junctions
follows the Poole-Frenkel mechanism, it deviates from both the Poole-Frankel
and Schottky mechanisms in Gr/Si and Gr/GaAs junctions, particularly for low
temperatures and fields.
