No abstract

Recent studies of electroluminescent cooling in III-V structures demonstrate the need to understand better the factors affecting the efficiency of light emission and energy transport in light-emitting diodes (LEDs). In this work, we establish the physical and operational requirements for reaching the efficiencies needed for observing electroluminescent cooling in III-V intracavity double diode structures at high powers. The experimentally-validated modeling framework used in this work, coupling the drift-diffusion charge transport model with a photon transport model, indicates that the bulk properties of the III-V materials are already sufficient for electroluminescent cooling. Furthermore, the results suggest that the bulk power conversion efficiency of the LED in the devices, that allowed the experimentally measured record high coupling quantum efficiency of 70%, already exceeds 115%. However, as shown here, direct observation of electroluminescent cooling by electrical measurements still requires a combination of a more efficient suppression of the non-radiative surface recombination at the LED walls and the reduction of the detection losses in the photodetector of the intracavity structures.

Fundamental thermodynamic considerations reveal that efficient emission from an electrically injected light emitting diode (LED) can lead to the cooling of the device. This effect, known as electroluminescent (EL) cooling, has been identified decades ago, but it has not been experimentally demonstrated in semiconductors at practical operating conditions due to the extreme requirements set for the efficiency of the light emission. To probe the conditions of EL cooling in GaAs based light emitters, we have designed and fabricated LED structures with integrated photodiodes (PDs), where the optically mediated thermal energy transport between the LED and the PD can be easily monitored. This allows characterization of the fundamental properties of the LED and a path for eliminating selected issues encountered in conventional approaches for EL cooling, such as the challenging light extraction. Despite several remaining nonidealities, our setup demonstrates a very high directly measured quantum efficiency of 70%. To characterize the bulk part of the LED, we also employ a model for estimating the power conversion efficiency (PCE) of the LED, without the contribution of non-fundamental nonidealities such as photodetection losses. Our results suggest that the PCE of the LED peaks at around 105-115%, exceeding the 100% barrier required to reach the EL cooling regime by a clear margin. This implies that the LED component in our device is in fact cooling down by transporting thermal energy carried by the emitted photons to the PD. This provides a compelling incentive for further study to confirm the result and to find ways to extend it for practically useful EL cooling.Published under license by AIP Publishing. https://doi.

Current crowding close to electrical contacts is a common challenge in all optoelectronic devices containing thin current spreading layers (CSLs). We analyze the effects of current spreading on the operation of the so-called double diode structure (DDS), consisting of a light emitting diode (LED) and a photodiode (PD) fabricated within the same epitaxial growth process, and providing an attractive platform for studying electroluminescent (EL) cooling under high bias conditions. We show that current spreading in the common n-type layer between the LED and the PD can be dramatically improved by the strong optical coupling between the diodes, as the coupling enables a photo-generated current through the PD. This reduces the current in the DDS CSL and enables studying EL cooling using structures that are not limited by the conventional light extraction challenges encountered in normal LEDs. The current spreading in the structures is studied using optical imaging techniques, electrical measurements, simulations, as well as simple equivalent circuit models developed for this purpose. The improved current spreading leads further to a mutual dependence with the coupling efficiency, which is expected to facilitate the process of optimizing the DDS. We also report a new improved value of 63% for the DDS coupling quantum efficiency (CQE).

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