Design for enhanced thermo-electric pumping in light emitting diodes

Abstract

We present a strategy for optimization of thermo-electric pumping in light emitting diodes (LEDs). We use a finite element model for charge transport in a GaInAsSb/GaSb double hetero-junction LED that is verified experimentally to consider optimal design and operation of low-bias LEDs. The wall-plug efficiency is shown to be enhanced by over 200× at nanowatt power levels and 20× at microwatt power levels. A design for room-temperature operation of a 2.2 μm LED with 100% efficiency is proposed—this represents a 110 °C reduction of the temperature required to observe unity efficiency.

Electro-luminescent cooling in the deep sub-bandgap bias regime

“…Recent work by Dodd Joseph Gray, Jr., Rajeev J. Ram, and the author of this manuscript has made use of an experimentally-verified electron transport model to design an InGaAsSb LED for low-bias operation [24]. The design process in this regime is dominated by the need to enhance the device's low-bias quantum e ciency ⌘ 0 EQE , because this quantity directly determines both the low-power e ciency and the maximum optical power density available at unity e ciency.…”

“…In particular the main aim of previous work on electro-luminescent cooling, to build a practical device capable of vibration-free solid-state cooling, remains many orders of magnitude in power density away. Nevertheless, much of this di↵erence may be possible to overcome through the explicit design of light-emitting diodes for lower voltages than are currently designed for [10,24]. Although the low-bias regime V ⌧ k B T /q necessarily constrains the electrically-driven optical power density to below that of equilibrium blackbody radiation, design for higher biases which are still several k B T below E gap remains largely unexplored.…”

Leakage currents of large area InP/InGaAs heterostructures

“…Ideally the high IQE is expected to enable electroluminescent (EL) cooling [2] as well as thermophotonic (TPX) coolers with a cooling capacity of several Watts per cm 2 of emitter area over large temperature differences [3]. While electroluminescent (EL) cooling at these power levels and in the high IQE regime is yet to be demonstrated, the expectations for functional thermophotonic coolers have very recently been reinforced by the demonstrations of EL cooling in GaSb/InGaAsSb LEDs [4,5]. The cooling in these demonstrations took place under very low bias voltages where the IQE is very small, but nevertheless demonstrated electricity-to-light conversion efficiencies exceeding unity by a large margin.…”

A design of a PhC-enhanced LED for electroluminescence cooling

“…In order to enhance the output power, Gray et al optimized the doping concentration and the active region thickness of a GaInAsSb/GaSb LED and the output power of the redesigned LED at η W P E = 1 was enhanced by a factor of 621 at room temperature. 15 However, considerably higher output power is still desired to overcome the convection heat flux which is approximately 2 mW/cm 2 for a 1 K temperature difference in the air. 16 To the best of our knowledge, a direct measurement of the ELC temperature drop has not been reported.…”