Researchers from the University of California, Berkeley, led by Dr. N. Sherlekar, have made significant strides in understanding and controlling two-dimensional (2D) excitons in gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) heterostructures. Their work, published in the journal Physical Review Letters, could have practical applications in the energy sector, particularly in the development of more efficient optoelectronic devices.
The team investigated electroluminescence (EL) from dopant-free ambipolar lateral p-n junctions in GaAs/AlGaAs single heterointerface (SH) heterostructures. Electroluminescence is the phenomenon where a material emits light in response to an electric current passed through it or to a strong electric field. This is crucial for devices like LEDs and solar cells.
The researchers observed bright electroluminescence from neutral free excitons, which are bound states of electrons and holes that can move freely within a material. They identified two types of excitons: the heavy-hole neutral free exciton (X^0) and the high-energy free exciton of the H band (HE). The EL spectra revealed that the peak energies of X^0 were slightly higher than those observed in bulk GaAs photoluminescence (PL) measurements, indicating that the excitons were confined to the interfacial layer.
Time-resolved measurements showed that the lifetimes of the excitons in the EL process were significantly shorter than those in the PL process. This further supports the idea that the excitons are confined to a 2D layer at the heterointerface. The researchers also found that the energies and lifetimes of the HE exciton could be tuned by applying a topgate voltage, which could have implications for the development of tunable optoelectronic devices.
One of the most intriguing findings was the observation of the “tidal effect,” a form of pulsed electroluminescence generated by swapping the topgate voltage polarity in ambipolar field-effect transistors. This effect produced an X^0 line at the same energy as in the lateral p-n junction and reproduced a characteristic nonmonotonic frequency dependence of the brightness previously observed in quantum-well heterostructures. This indicates a 2D-like origin for the excitons.
The researchers concluded that their results demonstrate electrically generated and controllable 2D-like excitons (HE and X^0) in dopant-free GaAs/AlGaAs SH devices. This work bridges 2D exciton physics and 2D electron and hole gas (2DEG/2DHG) platforms, paving the way for the development of more efficient and tunable optoelectronic devices in the energy sector.
Source: Physical Review Letters
This article is based on research available at arXiv.