Extremely Low On-Resistance and High Breakdown Voltage Observed in Vertical GaN Schottky Barrier Diodes with High-Mobility Drift Layers on Low-Dislocation-Density GaN Substrates

Abstract

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density. High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements. The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 0.71 mΩ cm2 and over 1100 V, respectively. The figure of merit (VB2/RonA) was 1.7 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC.

Current status of GaN power devices

“…Recent research on diodes has indicated that the quality of GaN substrates has become high enough to apply them to high-voltage devices [28,29,30]. We have determined that edge and mixed (edge + screw) dislocations in the GaN substrate do not induce a leakage current even at a dislocation density of ∼10 6 cm −2 [31].…”

Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor

“…[15] and Saitoh et al [12] reported a DD of 1 × 10 6 cm −2 for MOCVD GaN Schottky diodes with a record power figure of merit of 1.7 GW cm −2 . When the HEMT surface is analyzed with SEM and atomic force microscopy (AFM), it is noticeable that the surface was composed of mounds, in the form of a truncated elliptical parabola (figure 2).…”

“…The highest quality GaN epitaxial layers would ideally be achieved by homoepitaxy using a GaN substrate which is identical in crystal structure, lattice constant and thermal expansion coefficient. This homoepitaxy template can be achieved by means of a freestanding (FS-GaN) crystal, (obtained after the growth and separation of several hundred micrometers of GaN on a foreign substrate), but such FS-GaN layers still contains several types of imperfections such as scratches and/or edge pits [10][11][12][13][14][15][16][17]. The inherent FS-GaN defects extend into the HEMT active layers and may degrade the charge transport mechanisms, particularly increasing the HEMT off-state leakage currents which, in turn, reduces the breakdown voltage.…”

Vertical gallium nitride schottky diodes for power switching applications.

“…HVPE produced GaN substrates were used to build Schottky rectifiers with threading dislocation densities < 1x 10 6 cm -2 and have exhibited n-type conductivity with resistivity value as low as .01 Ωcm. A 5 μm epitaxial layer was deposited on top of the bulk substrate using MOCVD [53] with Si concentration of 8x10 15 cm -3 . 1 μm thick PECVD deposited SiN X was used as the dielectric layer, and the field plate structure was formed by Schottky contact overlapped with dielectric as illustrated in the figure 2-8.…”

“…The goal of edge termination techniques is to achieve an electric field distribution as close to the ideal case as possible. A number of edge modification techniques have been used in the literature, such as field plates [53], damage implants [56], guard rings [33], and different combinations of these strategies [58][59][60], as shown in figure 2-11. In a field plate structure, the Schottky contact extends over the dielectric.…”