Graphene/p-AlGaN/p-GaN electron tunnelling light emitting diodes with high external quantum efficiency

Highlights: • An original physical picture regarding the tunnelling process is proposed leading to a double peaks graphene/AlGaN/GaN LED. • A high EQE of 55.8% under 5 mA current was realized by Al₂O₃ barrier and AlGaN/GaN interface barrier in the device. • As the Fermi level of graphene can be tuned by gating effect, a colour tuneable graphene/AlGaN/GaN LED was realized. -- Abstract: The realization of p-type conduction in GaN and commercialized GaN light-emitting diodes (LED) is accepted as an advance in the development of human society. Conventionally, LED is based on PN junction and the quantum wells are introduced for confining electrons and holes, which improves the external quantum efficiency (EQE). Herein, we realized a graphene/AlGaN/GaN LED emitting double peaks at 430 nm and 560 nm. The blue peak at 430 nm is originated from the recombination process between holes injected from graphene/AlGaN heterostructure and electron produced from the tunnelling and avalanche multiplication process in p-type AlGaN/p-type GaN interface. Compared with the bare p-type AlGaN/GaN heterostructure without blue light emission, the graphene/p-AlGaN enhances the hole injection process through the band gap alignment and the mediate thickness of p-AlGaN is important taking the hole transport in AlGaN into consideration. The AlGaN/GaN interface confines the produced electrons and thus result in a high EQE of 55.8% under 5 mA current after intercalating an Al₂O₃ barrier at the interface between graphene and AlGaN/GaN. Moreover, the tunable graphene/AlGaN/GaN LED with different intensity of 430 nm has been demonstrated through changing the Fermi level of graphene by gating effect. The graphene/AlGaN heterostructure induced confinement effect can bring a novel type of LED, which can be optimized for special applications.