Low-frequency noise characterizations on Ni/GaN Schottky diodes deposited on intermediate-temperature buffer layers

Silicon dioxide passivated back-to-back Schottky diodes were fabricated by depositing Ni on rf plasmaassisted molecular beam epitaxy-grown GaN utilizing a unique double buffer layer structure. In this study, both low-frequency noise and deep-level transient Fourier spectroscopy (DLTFS) measurements were conducted to characterize the effects of intermediate-temperature buffer layers (ITBLs) on the hot-electron hardness of GaN Schottky diodes. Device A was fabricated with a double buffer layer consisting of a thin AlN high-temperature buffer layer (HTBL) and a GaN ITBL. Device B consists of a single AlN HTBL. Low-frequency noise results measured from the as-deposited devices show a significant reduction in the noise level, over an order of magnitude, for device A indicative of the substantial reduction in the trap density in the GaN thin films deposited on ITBLs. Hot-electron hardness of the devices was examined through the application of high voltage stress. The increase in the low-frequency noise for device A after voltage stressing is much smaller and no detectable deep-level is observed by both low-frequency noise and DLTFS techniques. However, both characterization techniques indicate a generation of a deep-level at 780 meV below the conduction band edge for device B. Based on detailed optical and electrical characterizations of the samples, the improved device properties for device A are attributed to the relaxation of residue strain in the epilayer during growth due to the utilization of ITBL.