The Effect of Annealing on Argon Implanted Edge Terminations for 4H-SiC Schottky Diodes
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THE EFFECT OF ANNEALING ON ARGON IMPLANTED EDGE TERMINATIONS FOR 4H-SIC SCHOTTKY DIODES A P KNIGHTS*, D J MORRISON**, N G WRIGHT**, C M JOHNSON**, A G O'NEILL**, S ORTOLLAND** , K P HOMEWOOD*, M A LOURENqO*, R M GWILLIAM*, AND P G COLEMAN***, *School of Electronic Engineering, Information Technology and Mathematics, University of Surrey, Guildford GU2 5XH, United Kingdom. [email protected] **Department of Electrical and Electronic Engineering, University of Newcastle, Newcastleupon-Tyne, United Kingdom, NEI 7RU. ***School of Physics, University of East Anglia, Norwich, NR4 7TJ, United Kingdom. ABSTRACT The edge termination of SiC by the implantation of an inert ion species is used widely to increase the breakdown voltage of high power devices. We report results of the edge termination of Schottky barrier diodes using 30keV Ar÷ ions with particular emphasis on the role of postimplant, relatively low temperature, annealing. The device leakage current measured at 100V is increased from 2.5nA to 7pA by the implantation of 30keV Ar÷ ions at a dose of lxl005 cm-2. This is reduced by two orders of magnitude following annealing at 600°C for 60 seconds, while a breakdown voltage in excess of 750V is maintained. The thermal evolution of the defects introduced by the implantation was monitored using positron annihilation spectroscopy (PAS) and deep-level-transient spectroscopy (DLTS). While a concentration of open-volume defects in excess of lxlO19 cM-3 is measured using PAS in all samples, electrically active trapping sites are observed at concentrations ~lxlO1 5cm 3 using DLTS. The trap level is well-defined at Ec-E, = 0.9eV. INTRODUCTION SiC Schottky barrier diodes are ideal for power switching applications as they can be operated at higher voltages and higher temperatures than equivalent Si or GaAs devices. The requirements for a high power Schottky barrier diode are a low forward voltage drop, low reverse leakage current and high breakdown voltage. Premature voltage breakdown often occurs because of electric field crowding at the periphery of the device. In order to achieve high breakdown voltages near to the theoretical limits expected for SiC, it is necessary to employ an edge termination. One technique used to terminate Schottky diodes is via the implantation of inert ions. The main area of the device is protected using a mask and inert ions are implanted into the sample. This process forms an area of high resistivity which allows the potential to spread across the surface of the biased sample. Unfortunately, a significant and undesirable increase in leakage current accompanies the increase in breakdown voltage. For example, devices exhibiting near-ideal breakdown voltages on 6H-SiC have been reported using Ar÷ ion implantation [1], however the reverse leakage of these devices was 5x10-2A/cm 2 at
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