Influence of Surface Recombination on Forward Current–Voltage Characteristics of Mesa GaN $\hbox{p}^{+}\hbox{n}$ Diodes Formed on GaN Free-Standing Substrates

Abstract

The influence of surface recombination on forward current-voltage (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> ) characteristics of gallium nitride (GaN) p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> and 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> <; 2.9 V) is dominated by carrier recombination at the side surface of the etched n GaN. The I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> characteristics of the fabricated diodes were compared with the reported GaN p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> n diodes with almost-zero overetched depth of n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> GaN. The large I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> of the latter diodes is attributed to enhanced photon recycling through photon reflection at the metal mirror. Moreover, reducing S to less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cm/s is considered indispensible for achieving similar enhanced photon recycling in overetched terminated diodes.