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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.

A type of broadband (325−980 nm) self-powered photodetector based on graphene/GaAs van der Waals heterojunction is reported. By simply spinning a layer of Ag nano-particles (Ag NPs) onto graphene/GaAs heterostructure, the responsivity and detectivity of our devices for the whole spectrum range are enhanced significantly. The maximum photocurrent responsivity of 210 mA W−1 (increased by 38%) and detectivity of 2.98 × 1013 Jones (increased by 202%) are achieved at 405 nm, which is about two or three orders of magnitude larger than other graphene based self-powered photodetectors. The mechanism of the improvement originates from the overlap the depletion region of graphene/GaAs heterostructure, the surface plasmon enhanced light field region below the surface and the light absorption region of the GaAs layer. The external quantum efficiency (EQE) measurement, transient photoluminescence (PL) test and the comparative theoretical simulation show that the surface plasmon enhancement should only be applicable for graphene/direct band gap semiconductor heterostructure, where the semiconductor should have a high optical absorption coefficient. The obtained high performance broadband photodetector with excellent detectivity is a promising candidate for many important optoelectronic applications, such as ultrasensitive image sensor in charge coupled displayer field, which requires colour sensors not only with high photo responsivity but also in a wide spectral range.

As a typical two-dimensional (2D) atomic thin material, the massless Dirac Fermions in graphene promise many unique physical properties, such as high carrier mobility and high light transmission. However, after a decade of research and a huge number of papers focusing on graphene, high performance graphene based optoelectronic devices is still lacked, which should be achieved for realizing competitive industrial graphene product. In this review, we point out high performance optoelectronic devices such as solar cells, photodetector and light emitting diodes can be demonstrated by properly marrying graphene with semiconductor. The fundamental physics of graphene/semiconductor heterostructure as well as its optoelectronic properties are comprehensively addressed. We suggest six strategies of improving the performance of graphene/semiconductor based optoelectronic devices. The outstanding light harvesting enhancement characteristic of surface plasmon is detailed represented to highlight its importance and potential. Especially, we indicate that graphene/semiconductor heterostructure solar cell can reach a power conversion efficiency of 30%.