Mid-infrared Electroluminescence from Surface Plasmon Coupled InAs Quantum Dots
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1208-O07-02
Mid-infrared Electroluminescence from Surface Plasmon Coupled InAs Quantum Dots Brandon Passmore,1 David Adams2, Troy Ribaudo,2 Dan Wasserman2, Stephen Lyon3 and Eric Shaner1 1 Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185, USA 2 Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, MA 01854, USA 3 Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
ABSTRACT The mid-infrared spontaneous emission from intersubband energy transitions in selfassembled InAs quantum dots is demonstrated with plasmonic top contact output couplers. Electrically pumped devices having subwavelength meshes designed to exhibit extraordinary optical transmission from 9 – 12 µm are measured and compared to a reference device with an open area contact. From additional patterning on the top contact, the signal-to-noise ratio was 4 times greater than the reference device. Beyond simply filtering the emission spectra of the quantum dot material, an emission null is observed which we link to the dots being in the near field region of the plasmonic coupler.
INTRODUCTION Proposed in the early 1970s [1,2] and first demonstrated in 1994 [3], quantum cascade lasers (QCLs) are emerging mid-infrared (mid-IR) to far-infrared light sources with critical applications including spectroscopy [4], free space optical communication [5], and national security[6]. Although significant advances have been made in improving QCL device performance, it is desirous to further improve efficiency. If the active region of the device is based on three-dimensional confinement, such as a quantum dot (QD), a phonon bottleneck may be created making nonradiative recombination between conduction electron states more difficult and offering a potential path forward to enhanced efficiency [7]. At the same time, there has been an increased effort to improve the spontaneous emission efficiency of light emitting diodes (LEDs) by coupling to surface plasmons (SPs) [8]-[11]. When the active region of the LED is grown close the metal/semiconductor interface, strong electrodynamical coupling between the active region and SP takes place [12]. Although most of this work focuses on GaN based LEDs, the same principles are relevant at longer wavelengths. In this work, plasmonic structures are fabricated on electrically pumped mid-IR QD emitters. Our results indicate that plasmonic structures can significantly alter the emission spectra of such devices potentially enabling both quantum and electrodynamic improvements to be made in three-dimensionally confined structures.
EXPERIMENT The InAs QDs were grown in GaAs/AlGaAs heterostructures and were designed to maximize current injection into excited conduction band states while removing electrons from the ground states within the conduction band; a similar approach to that of QCLs, using dots instead of wells as the active region. A schematic of the conduction band diagram is displayed in Fig. 1.
hυ
n-GaAs
GaAs
Al0.3Ga0.7As
GaAs
Al0.3G
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