GaN-based avalanche photodiodes

Visible-blind UV sensors for applications that require both wide bandwidth and high sensitivity will benefit from avalanche photodiodes (APDs) that have an internal gain mechanism. This paper reports the first clear observation of avalanche multiplication gain in an ultraviolet photodiode fabricated in the III-V materials system. The photodiodes were fabricated from GaN layers grown on a sapphire substrate by hydride vapour phase epitaxy (HVPE) (Molnar et al., J. Crystal Growth, vol. 178, 147, 1997). First, a 10 /spl mu/m thick layer of n-type GaN was deposited, followed by a 0.25 /spl mu/m thick Zn-doped "i" layer. Circular mesas of 30 /spl mu/m diameter were formed by reactive ion etching and were contacted with a semitransparent Ti film.