High current density electrical test was performed on SiC Schottky diodes. The shift in the Schottky barrier height was suppressed by adopting Mo2C as an electrode. Physical analysis revealed an epitaxial growth of Mo2C on SiC surface, which may be the origin of the stability.
Introduction
SiC Schottky barrier diodes (SBD) are used for high efficiency power conversion circuit owing to its high breakdown voltage, low ON-resistance and fast operation speed. However, pure metal and SiC surface reacts during high temperature annealing, forming an inhomogeneous interface [1]. Therefore, there is a concern in the diode characteristics change with time. We have shown diode characteristics with high temperature stability by using Mo2C as Schottky electrodes [2]. In this report, electric characteristics of SiC-SBD with Mo or Mo2C electrode when this devices is applied current of high current density and TEM analysis of Mo2C/SiC interface with high temperature stability are reported.
Experiments
A SiC wafer used in this study is an epitaxially grown 4°-off n-type 4H-SiC (0001) with a donor concentration of 1015cm-3 on a SiC substrate. Mo or Mo2C electrodes were sputter-deposited and patterned by reactive ion etching. The Mo and Mo2C samples were annealed in 500 or 850oC, respectively. Diode characteristics were measured before and after flowing a current density of 100A/cm2 for 500 s.
Results and discussions
The diode characteristics before and after the electrical current test are shown in fig. 1. Although increase in the Schottky barrier height was observed in both diodes, the amount of shift was suppressed with the Mo2C diode. This fact suggests that local interface reaction due to inhomogeneous current flow was suppressed. Moreover, only a slight degradation in the ideality factor was suppressed with the Mo2C electrode. Transmission electron microscope image of the diode, shown in fig. 2, revealed an epitaxial growth of a Mo2C layer on the SiC surface. The reliable diode characteristics might be originated from the sharp and uniform interface.
Conclusion
An electrical current test was performed on SiC Schottky diodes with Mo2C electrodes. A stable Schottky barrier height with a robust ideality factor was observed.
TEM analysis revealed an epitaxial growth of Mo2C on the SiC surface with a sharp and uniform interface.
References
[1] L. Kolaklieva, et al., ISBN 978-953-307-027-8, (2009) [2] T. Suzuki, et al., IEEE Electron Dev. Lett., 37, 618 (2016)