Metal-insulator-semiconductor structure for deep-ultraviolet light-emitting diodes to increase the electron injection in the cathode region

摘要

In this work, we propose using metal-insulator-semiconductor (MIS) structure on the n-AlGaN layer to reduce the contact resistance and improve the wall-plug efficiency (WPE) for AlGaN based deep ultraviolet light-emitting diodes (DUV LEDs). The thin insulator between the cathode metal and the n-AlGaN layer can share the bias, which makes the n-AlGaN layer surface less depleted and thus the MIS-type cathode structure favors the intraband tunneling effect for electrons. Moreover, the adoption of the MIS-structure aligns the electron affinity for the metal above the conduction band for the n-AlGaN layer, and this avoids the electron transport by thermionic emission. Thanks to the MIS-type cathode, we find that excellent electron transport can be obtained even if the metal with big electron affinity is used. This work also conducts an in-depth investigation into the impact of the relative dielectric constant, the bandgap, the affinity, the length and the thickness for the insulator on the electron transport and the WPE of DUV LEDs. We find that an insulator with a small dielectric constant is required for promoting the electron tunneling in the MIS-type cathode region.