The influence of surface recombination on forward current-voltage (I F -V F ) characteristics of gallium nitride (GaN) p + n diodes formed on GaN free-standing substrates was both experimentally and computationally investigated. In the temperature range of 373-273 K, the surface-recombination velocity 5 of 0.5-μm n GaN overetched circular-mesa diodes was derived, respectively, as 2-10 × 10 7 and 1 × 10 7 cm/s for diodes with and without a mesa-field-plate termination structure consisting of dielectric and metal layers. It was shown that IF (V F <; 2.9 V) is dominated by carrier recombination at the side surface of the etched n GaN. The I F -V F characteristics of the fabricated diodes were compared with the reported GaN p + n diodes with almost-zero overetched depth of n - GaN. The large I F of the latter diodes is attributed to enhanced photon recycling through photon reflection at the metal mirror. Moreover, reducing S to less than 10 5 cm/s is considered indispensible for achieving similar enhanced photon recycling in overetched terminated diodes.