Influence of Surface Recombination on Forward Current–Voltage Characteristics of Mesa GaN Diodes Formed on GaN Free-Standing Substrates

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 × 10⁷ and 1 × 10⁷ 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 10⁵ cm/s is considered indispensible for achieving similar enhanced photon recycling in overetched terminated diodes.