Electroluminescent Behavior of Defects in 4H-SiC Light Emitting Diodes

In this work, electroluminescence in pn-junctions with various geometries in $\mathbf{4 H - S i C}$ is investigated. Under forward bias, all devices exhibit the nitrogen donor to valence band transition, emitting light at wavelengths of 391 nm and 400 nm. Additionally, light with a peak wavelength of 476 nm is emitted, corresponding to the nitrogen donor to $\mathbf{D}_{1}$ defect transition. Devices with significant areas of aluminum and nitrogen co-doping in their pnjunctions, feature another peak at 496 nm, resulting from the transition between the nitrogen donor state and the $\mathbf{A l}_{2}$ acceptor state, located deep within the bandgap. The peaks of the latter transition display a blue shift due to the Stark effect. At elevated device temperatures a red shift of all peaks is observed due to self-heating. The spectra obtained from the wafer's backside are compared with the absorption characteristics of the substrate, revealing that light stemming from the nitrogen donor to $D_{1}$ defect transition is absorbed dominantly by the substrate.