  Geometric diodes, which take advantage of geometric asymmetry to achieve
current flow preference, are promising for THz current rectification. Previous
studies relate geometric diodes' rectification to quantum coherent or ballistic
transport, which is fragile and critical of the high-quality transport system.
Here we propose a different physical picture and demonstrate a robust current
rectification originating from the asymmetric bias induced barrier lowering,
which generally applies to common semiconductors in normal environments. Key
factors to the diode's performance are carefully analyzed, and an intrinsic
rectification ability at up to 1.1 THz is demonstrated.
