Mid-wavelength infrared photodetection and surface plasmon enhancement
Date of Issue2018-08-13
School of Electrical and Electronic Engineering
Infrared (IR) photodetectors with peak sensitivity wavelength in mid-wavelength infrared (MWIR) spectral window (3-5 μm) have attracted extensive interests due to the highest atmospheric transmission in this range. Traditional photodetectors operating in this wavelength range are mainly based on HgCdTe, PbSnTe and InSb, which either have difficulties in repeatable growth of uniform composition bulk crystals and epitaxial layers or need low temperature environment, which lead to the development of alternative material systems, such as InAs/GaSb type-II superlattice (SL) and InAsSb based material system. To improve high temperature performance of photodetectors, a concept of surface plasmon polariton (SPP) enhancement has been proposed in recent years. By placing a plasmonic structure which has strong light focusing capability in sub-wavelength regime, close to absorption region of a detector, tight spatial confinement and high local field intensity of surface plasmons enable to enhance light-matter interaction and thus to improve the performance of light detection. A practical and efficient way is to integrate a sub-wavelength metallic two-dimensional hole array (2DHA) and an absorption structure. Simulation and analysis of extraordinary optical transmission (EOT) through sub-wavelength metallic 2DHA, the underlying physics and mechanism of plasmonic enhanced photodetection have been studied. Possible variables and parameters which may affect the transmission and enhancement of photodetector performance have been analyzed. These include periodicity of hole array, hole diameter, refractive index of substrate, thickness of metal film, hole shape and light incident direction. The simulation results provide a good guide for design of 2DHA photodetectors. The origin of Wood’s anomaly in optical transmission through metallic hole array has been analyzed. Here, the contradiction of the existence of Wood’s anomaly in EOT and the generally observed broadband performance enhancement of photodetector via 2DHA is successfully explained. It is interpreted that at Wood’s anomaly wavelength, the extremely low transmission results from excitation of incident light as SPP, which has a low efficiency of being decoupled from the metal-dielectric interface and doesn’t contribute to transmission. Also, how this theory can be applied to illustrate the broadband photoresponse enhancement of integrated structure of photodetector and metallic hole array is described. A n-i-p based mid-infrared InAs/GaSb type-II superlattice (SL) photodetector working at 220 K has been designed and fabricated. According to characterization results, the grown SL structure has very high quality. At 220 K, the 50% cutoff wavelength of the photoresponse is about 4.66 µm, the R0A is as high as 14.9 Ω·cm2, and the dark current is very low. The peak detectivity of the photodetector is 2.23×10^10 Jones at 3.0 µm under zero bias, which is the highest for the InAs/GaSb SL photodetector operating at 220 K. High performance InAsSb based photodetector operating at room temperature has been fabricated and investigated. The InAsSb material is grown on the GaSb substrate by molecular beam epitaxy (MBE) and photoconductive detector is made by them. The grown materials show high quality and slight lattice mismatch to the substrate. The photoconductors fabricated based on the InAsSb/GaSb structure show spectral response ranging from near infrared (NIR) to MWIR range. They can work well at low voltage bias and the measured blackbody detectivities are ~2.4×10^7 Jones and ~6.1×10^9 Jones at room temperature and 77 K, respectively. Photodetection performance of n-GaSb/n-InAsSb heterostructure at different temperatures and biases has been investigated. The devices were found to be capable of dual color photodetection at fixed large forward biases at different temperatures and the maximum responsivity occurs at room temperature. As the forward bias decreases, a turning bias exists at which the photocurrent changes its direction and the voltage value varies with temperature. At reverse biases, the absorption of GaSb dominates the photocurrent and the maximum photocurrent occurs at about 205 K. All the observation can be explained by the proposed model. Plasmonic enhanced infrared photodetection based on n-GaSb/n-InAsSb heterostructure is realized and investigated. By integrating properly designed sub-wavelength metallic 2DHA on top, the room temperature photocurrent and detectivity of the photodiode is enhanced by ~2 times. Besides, the dark current of the heterostructure is not adversely affected by 2DHA fabricated on top. The performance enhancement is due to higher quantum efficiency of the 2DHA-heterostructure, resulting from electric field concentration at the metal-dielectric interface.
DRNTU::Engineering::Electrical and electronic engineering