Roles of lightly doped carbon in the drift layers of vertical n-GaN Schottky diode structures on freestanding GaN substrates

Abstract

We studied the roles of lightly doped carbon in a series of n-GaN Schottky diode epitaxial structures on freestanding GaN substrates, and evaluated the effects of the doping on diode performances. A large variation of compensation ratio was observed for carbon doping at (1-2) ' 10 16 cm %3 . A model was proposed to explain this phenomenon, in which a vulnerable balance between donor-type C Ga and deep acceptor C N strongly affected the free-carrier generation. Application of Norde plots and reverse biased leakage current in current-voltage measurements suggested provisional optimization for a free-carrier concentration of 8 ' 10 15 cm %3 to achieve a tradeoff between breakdown voltage and onresistance of the n-GaN diodes.

Hydride-vapor-phase epitaxial growth of highly pure GaN layers with smooth as-grown surfaces on freestanding GaN substrates

“…The peaks near 2.2 and 2.9 eV correspond to the yellow (YL) and blue (BL) luminescences usually observed for MOCVD-grown layers. 13,15) In the PL spectrum for the HVPE-grown sample, a weak deep level emission was also observed in the green spectral range (2.4 eV), despite the absence of any detectable impurities in the SIMS measurement. The BL emission was almost absent in this sample.…”

“…Although the above mentioned studies have shown the potential benefits of GaN-based vertical-type power devices, it remains difficult to produce high-purity layers of GaN by MOCVD due to the presence of residual carbon impurities in the range 10 15 to 10 17 cm −3 . 5,[13][14][15] The enhanced incorporation of carbon under the high-growth-rate conditions needed to produce thick drift layers 15) is another potential obstacle to the application of the MOCVD method in future mass production of power devices.…”

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

“…These samples are the same as those reported in Ref. . Free‐standing GaN substrates were prepared by the unique void‐assisted separation (VAS) technology of SCIOCS, which is based on the HVPE method .…”

“…We have reported electrical properties of Schottky diodes that are formed on low‐carrier thick n‐GaN layers with a variety of Si and C doping concentrations . A free carrier concentration of 8 × 10 15 cm −3 was suitable for GaN Schottky diodes with both low on‐resistance and high‐breakdown performance.…”

Effect of Wafer Off‐Angles on Defect Formation in Drift Layers Grown on Free‐Standing GaN Substrates

“…In a previous work, we studied n‐GaN Schottky diodes with ten different carrier concentrations in the drift layer and reported 1) a provisional optimization of the free‐carrier concentration as low as 8 × 10 15 cm −3 in a trade‐off relationship between the breakdown voltage and series resistance, 2) a site change of C atoms from acceptor type to donor type when n < 1.5 × 10 17 cm −3 , and 3) suppression of deep‐level traps with the energy level from the conduction band ( E C ) to 0.9 eV deep through optimization of the growth conditions . We also investigated the wafer‐scale surface morphology of GaN free‐standing substrates and characterized the spatial distribution of the electrical and optical properties over the wafers .…”