Mapping of n‐GaN Schottky Contacts With Wavy Surface Morphology Using Scanning Internal Photoemission Microscopy

Abstract

We characterized the effects of surface morphology on the electrical properties of n‐GaN drift‐layers by using scanning internal photoemission microscopy (SIPM). We grew 12‐μm‐thick low carrier concentration (approximately 1 × 1016 cm−3) n‐GaN layers with both flat and wavy surface morphologies on freestanding GaN substrates by metal organic chemical vapor deposition. In the SIPM results, the samples with flat surfaces exhibited a uniform photocurrent distribution independently of the carrier concentration. In contrast, wavy patterns in the photocurrent maps were the same as the surface morphology for samples with low carrier concentration. These results indicate that the amount of C incorporated during the growth was affected by the off‐angle of the GaN surface, and the carrier compensation by C atoms was changed. We demonstrated that SIPM is a powerful tool for nondestructively visualizing the inhomogeneity of the carrier compensation over the wafers.

Vertical GaN p–n diode with deeply etched mesa and the capability of avalanche breakdown

“…It is considered that the sparse emission at avalanche breakdown reflected the internal compensation of carbon and nonuniformity of donor incorporated in bunched step edge. [30][31][32] In summary, we greatly reduced the leakage current and improved the breakdown voltage of a GaN p-n diode using a vertically and deeply etched mesa structure. We also succeeded in observing a stable nondestructive voltage breakdown and obtained evidence by evaluation of the temperature dependence that this phenomenon was an avalanche breakdown.…”

Elimination of macrostep-induced current flow nonuniformity in vertical GaN PN diode using carbon-free drift layer grown by hydride vapor phase epitaxy

“…14) The presence of irregular morphology, such as the macrosteps frequently observed in thick GaN drift layers grown homoepitaxially on GaN free-standing substrates, also complicates the situation, inducing inhomogeneous carrier concentrations across the electrode and wafers, as revealed by recent microscopic photoluminescence (PL), microscopic electroluminescence (EL), and photoemission microscopy observations. 15,16) This microscopic nonuniformity in the carrier concentration was tentatively attributed to off-angle-dependent incorporation of Mg or carbon in these works. Irrespective of the origin of the nonuniform carrier concentration, lower performance and yield were reported for vertical homoepitaxial GaN PNDs grown by MOCVD (MOCVD-PNDs) on a rough surface compared to those of diodes on a flat surface.…”

Mapping of contactless photoelectrochemical etched GaN Schottky contacts using scanning internal photoemission microscopy—difference in electrolytes

“…We have reported that incorporated C atoms during the MOCVD growth affected carrier compensation when Si doping concentration was as low as low 10 16 cm −3 or below. 33) In addition, the amount of the C atoms incorporated depends on an off-angle of the GaN surface. 34) One possible explanation for the variations of the measured donor concentrations is by such compensation.…”