GaN nanostructured $p-i-n$ photodiodes

We report the fabrication of nanostructured $p-i-n$ photodiodes based on GaN. Each device comprises arrays of $∼200nm$ diameter and $520nm$ tall nanopillars on a $1μm$ period, fabricated by e-beam lithography. Strong rectifying behavior was obtained with an average reverse current per nanopillar of $5fA$ at $−5V$⁠. In contrast to conventional GaN diodes, nanostructured devices reproducibly show ideality factors lower than 2. Enhanced tunneling through sidewall surface states is proposed as the responsible mechanism for this behavior. Under backillumination, the quantum efficiency in nanostructured devices is partly limited by the collection efficiency of holes into the nanopillars.