We report bright electroluminescence from ambipolar gate-defined lateral $p\text{–}n$ junctions and field effect transistors in dopant-free GaAs/AlGaAs single heterojunctions. A combination of transition energies, lifetimes, and spatial emission profiles as a function of gate voltage, forward bias, temperature, and RF excitation points to free excitons with a predominantly two-dimensional (2D) character, despite the lack of a bottom barrier providing physical confinement. Comparisons with time-resolved photoluminescence further support our findings. We develop an analytical model to explain our results based on the partial screening of electric fields within our devices. Collectively, our results show electrically generated and controllable 2D free excitons, bridging 2D exciton physics and ambipolar gate-defined two-dimensional electron gas/two-dimensional hole gas platforms.

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• Electroluminescence
• Excitons
• Optoelectronics
• Diodes
• III-V semiconductors
• Transistors
• Two-dimensional electron system
• Hall bar
• Infrared spectroscopy
• Molecular beam epitaxy
• Photoluminescence