Effects of electric polarization and defect energy levels induced by ion irradiation on the electrical behavior of 4H-SiC Schottky barrier diodes

Abstract

The effects of electric polarization and defect energy levels induced by C4+ irradiation on the electrical behavior of 4H-SiC Schottky Barrier Diodes (SBDs) are discussed. The parameters of the SBDs were extracted from capacitance-voltage (C-V) and current-voltage (I-V) measurements, the deep level transient spectroscopy (DLTS) was used to identify defect energy levels. In addition, the dielectric function and energy band structure of 4H-SiC were calculated using the first-principles approach to verify the enhancement of polarization and the origin of the defect energy levels. The results show that the net (donor) carrier concentration (Nd) increases with the increase of irradiation fluence, which is caused by the competition between irradiation-induced defects and the polarization effect. On the one hand, Z1/2 is determined by DLTS. It is related to the doubly negatively (2-|0) charged state of Vc (carbon vacancy), which is a double acceptor. The intensity of the Z1/2 peak increases with increasing irradiation fluence, which means that the defects caused by irradiation should reduce the Nd. On the other hand, the polarization effect does exist and it becomes stronger with the increase of the irradiation fluence, which makes the Nd increases. Obviously, the polarization effect induced by the irradiation is dominant for Nd when the depth of ion penetration is in the shallow layer behind the metal-semiconductor (M-S) interface. Irradiation induced electron traps and an uneven distribution of positively charged centers, which can cause ln(I)-V to exhibit a non-linear component before reaching the turn-on voltage. The series resistance (Rs), reverse current (IR) increases and the forward current decreases with the increase of irradiation fluence. All those show that the irradiation cause degradation of Ni/4H-SiC SBD performance.