Plasmon assisted photonic crystal quantum dot sensors

Abstract

We report Quantum Dot Infrared Detectors (QDIP) where light coupling to the self assembled quantum dots is achieved through plasmons occurring at the metal-semiconductor interface. The detector structure consists of an asymmetric InAs/InGaAs/GaAs dots-in-a-well (DWELL) structure and a thick layer of GaAs sandwiched between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The aperture of the detector is covered with a thin metallic layer which along with the dielectric layer confines light in the vertical direction. Sub-wavelength two-dimensional periodic patterns etched in the metallic layer covering the aperture of the detector and the active region creates a micro-cavity that concentrate light in the active region leading to intersubband transitions between states in the dot and the ones in the well. The sidewalls of the detector were also covered with metal to ensure that there is no leakage of light into the active region other than through the metal covered aperture. An enhanced spectral response when compared to the normal DWELL detector is obtained despite the absence of any aperture in the detector. The spectral response measurements show that the Long Wave InfraRed (LWIR) region is enhanced when compared to the Mid Wave InfraRed (MWIR) region. This may be due to coupling of light into the active region by plasmons that are excited at the metalsemiconductor interface. The patterned metal-dielectric layers act as an optical resonator thereby enhancing the coupling efficiency of light into the active region at the specified frequency. The concept of plasmon-assisted coupling is in principle technology agnostic and can be easily integrated into present day infrared sensors.

Optimization of Optoelectronic Plasmonic Structures

“…In addition, the hole-array structure allows transmission geometry which facilitates easy incorporation into present optoelectronic devices. So far, some experiments [6][7][8][9] based on the periodic holearray coupler have been carried out. For example, C. C.…”

Engineering of absorbing medium for quantum dot infrared photodetectors

“…Multiple approaches to tuning the QD medium along with device nanoengineering to improve coupling to external radiation to fit different requirements were developed. [2][3][4][5][6][7][8][9][10][11] An improved coupling by increase of photon lifetime was achieved by incorporating QD or quantum well IP media into photonic crystals 2,3 to increase absorption that allowed significant 100x reduction of media doping and hence decrease of dark current. Further improvement was achieved with plasmon coupling to a photonic crystal 4,5 that resulted in 15x detectivity enhancement.…”

Multispectral Quantum Dots-in-a-Well Infrared Detectors Using Plasmon Assisted Cavities

“…Gratings etched into the active region couple incident light into higher order modes enabling higher absorption [10], [11]. The use of dielectric and metallic deep etched photonic crystals have been attempted in the LWIR region [12], [13], but the high aspect ratio needed in etching makes processing difficult. Here we present a novel method whereby the spectral and polarization response of a DWELL detector is tuned by coupling the absorption of the active region to the resonant modes of a surface plasmon cavity integrated with the detector.…”