Carrier lifetime and breakdown phenomena in SiC power device material

Abstract

Recent progress and current understanding of carrier lifetimes and avalanche phenomena in silicon carbide (SiC) are reviewed. The acceptor level of carbon vacancy (VC), called the Z1/2 center, has been identified to be the primary carrier lifetime killer in SiC. The VC defects can be eliminated by the introduction of excess carbon atoms followed by carbon diffusion in the bulk region. The true bulk lifetime after VC elimination was estimated to be approximately 110 µs. The doping dependence of carrier lifetimes in n- and p-type SiC is also presented. The impact ionization coefficients of electrons and holes were extracted in the temperature range of 298 to 423 K. The intrinsic critical electric field strength of SiC〈0 0 0 1〉 was determined to be 2.0, 2.5, and 3.3 MV cm−1 for doping densities of 1 × 1015, 1 × 1016, and 1 × 1017 cm−3, respectively, at room temperature; it slightly increased at elevated temperature. The obtained set of impact ionization coefficients has enabled us to accurately predict the breakdown voltage of SiC devices, including its temperature dependence. Due to the unusually low impact ionization coefficient of electrons, the breakdown voltage of a SiC p+n junction is about 6%–9% higher than that of an n+p junction with a given doping density.

The Optimization of 3.3 kV 4H-SiC JBS Diodes

“…This bipolar device showed a typical PiN response, turning on at approximately 2.7 V, but with a slightly reduced R ON,SP of 11.9 m.cm 2 . While this is about 4 m.cm 2 lower than the other devices, a lifetime enhancement process [31] would boost conductivity modulation and reduce this further. Despite this, R ON,SP agrees with the already reported values for similar SiC unipolar power diodes [21].…”

High-voltage SiC power devices for improved energy efficiency

“… 35 , 36 ) However, the large anisotropy in the electron impact ionization coefficients cannot be explained simply by this relatively small anisotropy in the effective mass near the conduction band bottom and it may originate from the unique structure of the conduction band of SiC. 37 ) Because of the peculiar 〈0001〉 stacking structure of SiC with a four Si-C bilayer period (Fig. 4 (a)), there exist a few minigaps along 〈0001〉 in the k (wavevector)-space inside the conduction band, as shown in Fig.…”

“…Figure 18 (a) shows the inverse of the carrier lifetime versus carbon vacancy density obtained for very thick and lightly-doped SiC epitaxial layers. 37 , 63 ) The author’s group identified that a carbon vacancy defect creates multiple deep levels called “Z 1/2 center” in the bandgap of SiC by combining deep level transient spectroscopy (DLTS) and photo-excited electron paramagnetic resonance (EPR) measurements on specially-prepared SiC samples. 79 ) As shown in Fig.…”

“…Figure 19 (a) shows the depth profiles of the carbon vacancy density in SiC (260 µm-thick epitaxial layer) after thermal oxidation at 1400 ℃ for several different periods. 37 ) Here the depth profiles were acquired by repeating DLTS measurements and mechanical polishing. Figure 19 (b) shows a possible schematic image of the diffusion of carbon interstitials and elimination of carbon vacancies during thermal oxidation of SiC.…”

High-Temperature Impact-Ionization Model for 4H-SiC

“…However, for electrons, the impact ionization coefficient is assumed to be constant as a function of temperature. This assumption was extracted from calibrations below 425 K. Kimoto et al [31] are currently investigating this phenomenon and believe that this is due to conduction band minigaps (that form due to zone-folding) along the 0001 direction shrinking at high temperature.…”