Forward Voltage Drop Induced by an Abnormal Threading Dislocation Aggregation in 4H-SiC GTO Devices.

Yingxin Cui,Peng Dong,Zhiqiang Li,Juntao Li,Lianghui Li,Zhe Chen

doi:10.3390/ma12244042

Abstract

An abnormal star-like defect was found on the failed SiC gate turn-off thyristor (GTO) devices after metal removal and KOH etching at 450 °C in this work. It is of extraordinary larger size of 210–580 µm, even much larger than the etch pit of a micropipe in 4H-SiC. In addition, the abnormal star-like defect, exhibiting the consistent orientation with the six-fold symmetry of silicon carbide, was found to consist of several penetrating dislocations with the help of a LEXT OLS4000 3D laser confocal microscope. These abnormal star-like etch pits can severely reduce the forward blocking characteristic of GTOs, while exerting insignificant influence on the forward current-voltage characteristics between anode and gate electrode of the 4H-SiC GTO devices. Interestingly, the relationship between forward voltage drop and dislocation density is affected by the abnormal star-like defect. A regular increase of forward voltage drop at 100 A/cm2 was observed with the increasing dislocation density, while this correlation disappears in the presence of an abnormal star-like defect.

Highlights

Silicon carbide (SiC) is an attractive material for semiconductor devices operating under extreme conditions
An abnormal star-like defect was found after both metal removal and KOH etching at 450 °C on with threading screw dislocations and threading edge dislocations were reduced by 15.5% and 6.5%, the failed SiC gate turn-off thyristor (GTO) devices with lower breakdown voltage
Based on the above discussion, forward voltage drop induced by an abnormal threading dislocation forward blocking characteristic of 1.0 cm2 GTOs is severely deteriorated by this abnormal star-like aggregation in 4H-SiC GTO devices is elucidated

Summary

Introduction

Silicon carbide (SiC) is an attractive material for semiconductor devices operating under extreme conditions This is because of its extraordinary physical properties, such as high electrical break down field, high thermal conductivity, and high electron saturation velocity [1,2,3]. The conductivity modulated drift region of the GTO allows high voltages and high current densities while maintaining a low forward voltage [6] This conductivity modulation effect reduces the resistance of the thick, lowly-doped drift region that is required for blocking high voltages. This is achieved by the injection of carriers from adjacent device regions. Influence on the forward and blocking characteristic of SiC GTOs are investigated

Materials and Methods

An Abnormal Star-Like Defect

Morphology

Morphology and Structure of the Star-Like Defect

Conclusions