  We report low-frequency noise characteristics of vertical GaN PIN diodes,
focusing on the effects of the diode design, current and temperature. The
as-grown and regrown diodes, with and without surface treatment have been
studied. The noise in most of the GaN devices had a characteristic 1/f spectrum
at high and moderate currents, while some devices revealed
generation-recombination bulges at low currents (f is the frequency). The
predominant trend of the noise spectral density, S, dependence on the current
was S ~ I. All tested GaN PIN diodes had rather low normalized noise spectral
densities of 10^-18 cm2/Hz -- 10^-16 cm2/Hz (f=10 Hz) at the current density
J=1 A/cm2 at room temperature. The noise temperature dependences at different
currents revealed peaks at T=375 K -- 400 K. Temperature, current, and
frequency dependences of noise suggest that the noise mechanism is of the
recombination origin. We argue that the noise measurements at low currents can
be used to efficiently assess the quality of GaN PIN diodes.
