Optical Energy Transfer and Loss Mechanisms in Coupled Intracavity Light Emitters

Abstract

Despite the near-unity internal quantum efficiencies (IQEs) demonstrated for GaAs based light emitters, laser cooling of the ubiquitous III-V semiconductors has not been feasible. The key challenges for III-V optical cooling are the reduced absorption of the optical excitation at photon energies well below the band gap and the strong confinement of the light in the high refractive index semiconductors. Here we investigate the possibility to eliminate the need for light extraction and to eventually relax the requirements of the IQE. This is done by using electroluminescence and optical energy transfer within intracavity devices consisting of an AlGaAs/GaAs double heterojunction LED and a GaAs pn-homojunction photodiode enclosed within a single semiconductor cavity. We measure the intracavity energy transfer i.e. the coupling quantum efficiency (CQE) between the two diodes and estimate loss mechanisms by simultaneously measuring the IV-characteristics of the emitter diode and the photocurrent of the absorber diode. The measured CQE is below 60 % due to the mirror, light extraction, nonradiative and detection losses. While this is far below the state-of-the-art efficiencies, our results suggest that it will be possible to substantially improve the efficiency by adopting the fabrication and design principles used for the best performing photoluminescent emitters.

Thermophotonic cooling in GaAs based light emitters

“…1(a). 12 The DDS consists of two semiconductor diodes grown within a single epitaxial growth process, essentially forming a thermophotonic (TPX) heat pump system where light extraction is not necessary. The upper diode is a DHJ LED injected by an external current I 1 and voltage U 1 , while the lower diode is a homojunction photodetector (PD) absorbing light from the emitter and producing an external current I 2 .…”

Observation of local electroluminescent cooling and identifying the remaining challenges

“…In this paper, we generalize and summarize our previous results 4,5,13,14 on analyzing the performance of the DDS from the point of view of high-power EL cooling. Additionally, here we separately analyze the LED itself…”

“…fabricating thermophotonic heat pumps (THP) providing higher efficiencies than the existing solid state coolers, 3 ELC at powers sufficient for practical applications is still not demonstrated.To study high-power ELC we use double diode structures (DDSs), which consist of a double heterojunction (DHJ) LED and a photodiode (PD) grown within a single technological process and, thus, enclosed in a cavity with a homogeneous refractive index. 4,5 The presence of the PD in the structure allows to more directly probe the efficiency of the LED, without the need for light extraction from the system, reducing undesirable losses. Our analysis of experimentally measured I − V curves for both the LED and the PD suggests that the local efficiency of the high-performance LEDs we have fabricated is approximately 110%, exceeding unity over a wide range of injection current densities of up to about 100A/cm 2 .At present the efficiency of the full DDS, however, still falls short of unity, not allowing direct evidence of the extraction of thermal energy from the LED.…”

Temperature dependence of thermophotonic energy transfer in intracavity structures

“…The DDSs studied in this work consist of a double heterojunction (DHJ) GaAs/AlGaAs LED structures grown on top of a GaAs p-n-homojunction photodiode. 3 The basic device structure is shown in Fig. 1.…”