Abstract:
GaN epitaxial layers grown on SiC and sapphire suffer from high density of line and point defects. To address this problem, new growth methods using in situ or ex situ nano-network masks as dislocation filters have been introduced recently. In this work, we report on metalorganic chemical vapor deposition (MOCVD) of GaN layers on 2-inch sapphire substrates using in situ SiN x nano-networks intended for defect reduction. SiNx interlayers with different deposition times were employed after ∼2 μm GaN grown on sapphire, which was followed by ∼3.5 μm GaN overgrowth. With increasing SiNx coverage, full width at hall maximum (FWHM) values of (0002) and (101̄2) X-Ray diffraction (XRD) peaks monotonously decrease from 252 arc sec to 217 arc sec and from 405 ar csec to 211 arc sec, respectively for a 5.5 μm thick film. Similarly, transmission electron microscopy (TEM) revealed that screw and edge type dislocation densities as low as 4.4×107 cm-2 and 1.7×107 cm -2 were achieved. The use of SiNx nanonetwork also increases the radiative recombination lifetimes measured by time-resolved photoluminescence to 2.5 ns from less than 0.5 ns in control GaN. We have also fabricated Ni/Au Schottky diodes on the overgrown GaN layers and the diode performance was found to depend critically on SiNx coverage, consistent with TEM, XRD and TRPL results. A 1.13eV barrier height was achieved when SiNx layer was used compared to 0.78 eV without any SiN x nanonetwork. Furthermore, the breakdown voltage was improved from 76 V to 250 V with SiNx nanonetwork.
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