Electroluminescence in GaAs/AlGaAs single heterojunctions: 2D free exciton, H-band, and tidal effect

We demonstrate bright electroluminescence (EL) from dopant-free ambipolar lateral p–n junctions in GaAs/AlGaAs single heterointerface (SH) heterostructures. We characterize the heavy-hole neutral free exciton (X⁰) and the high-energy free exciton of the H-band (HE). Observations support 2D origins for both species. The X⁰ EL energies (1515.5-1515.7 meV) are slightly larger than the corresponding X⁰ photoluminescence (PL) energy (1515.3 meV) of bulk GaAs. Time-resolved measurements of the EL X⁰ and PL X⁰ yield lifetimes of 337 ps and 1610 ps, respectively. HE is blueshifted through the Stark effect in response to forward bias below threshold. We demonstrate gate voltage control of the HE energies and lifetimes (down to 575 ps). Above threshold, the intensity of HE decreases as a function of forward bias in favor of X⁰. Finally, we observe the tidal effect, a form of pulsed EL, in SH ambipolar field-effect transistors, which also shows a 2D X⁰. We reproduce the frequency-dependent brightness of the tidal effect previously reported in quantum well heterostructures. Mechanisms for the generation of 2D free excitons, uniquely enabled by the presence of a 2DEG and/or 2DHG, are discussed.