Spontaneous Conversion of Basal Plane Dislocations in 4° Off-Axis 4H–SiC Epitaxial Layers

Abstract

The conversion of basal plane dislocations (BPDs) to electrically benign threading edge dislocations in 4° off-axis 4H–SiC epilayers has been investigated using ultraviolet photoluminescence imaging. The conversion spontaneously occurred throughout the epitaxial layer for all substrates studied using similar epitaxial growth conditions. BPD conversion in highly doped epilayers was suppressed compared with lower n-type doped layers, suggesting that nitrogen concentration influences the conversion mechanism. However, it is technologically important for the conversion to occur in a heavily doped buffer layer. The densities of BPDs in low-doped (∼1014 cm–3) films having a thickness of 20 μm were significantly reduced when a ∼20 μm thick highly doped N+ buffer layer was grown between the low-doped layer and the substrate. Without the buffer layer, an average of ∼50 BPDs cm–2 was observed and with the buffer layer, an average of 1.5 BPDs cm–2 was detected; the best result was 0.2 BPD cm–2. A PiN structure consisting of a 25 μm thick N+ buffer layer to convert the majority of BPDs prior to the device structure was used to test the mitigation process, and the diodes demonstrated no forward voltage change after 225 h of continuous biasing at 100 A cm–2.