Influence of Surface Recombination on Forward Current-Voltage Characteristics of Mesa GaN p+n 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 S of 0.5-mu m n-GaN overetched circular-mesa diodes was derived, respectively, as 2-10 x 10(7) and 1 x 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 I-F (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.