DUVET

Light Emitting Diodes (LED) based on nitrides are very efficient and worldwide used for solid state lighting. In the ultraviolet, however, their wall plug efficiency remains severely limited by the p doping problem in AlGaN. This intrinsic problem can be circumvented by inserting a tunnel junction, which allows injecting holes in the LED and replacing the p contact by an n contact. The challenge is to obtain a low resistance in this tunnel junction in order to maximize the overall LED efficacy. The project aims at exploring all solutions to fabricate this junction, in particular the insertion of a thin InGaN layer in AlGaN, at studying carefully the role of defects in the junction and the physics of hole injection. A breakthrough in this domain would have a tremendous impact. For instance, water sterilization with UV at 275 nm could be easily extended in many countries and would allow saving thousands of lives in underdeveloped countries. A consortium of 3 laboratories (CRHEA, LETI, IEMN) will tackle this problem. TJs will be grown by a combination of gas phase and molecular beam epitaxies, which solves a problem of Mg activation. The role of defect at the interface, which is believed to increase the tunnel current, will be investigated by surface treatments, and chemical analyses, coupled with electrical measurements. The injection of out of equilibrium holes will be studied by growing dedicated structures. The goal is to reach a tunnel junction resistance lower than 0.001 ohmcm2 in TJ for LEDs emitting at 310 and 275 nm, and a wall plug efficiency of 1% at 275 nm.