Plazmonske strukture za poboljšanje poluprovodničkih infracrvenih detektora

Abstract

Plazmonika je jedna od oblasti nauke koje se u današnje vreme eksplozivno razvijaju. Ona je posvecena elektromagnetici nanokompozitnih metamaterijala koji podržavaju rezonanciju površinskih plazmona polaritona (surface plasmons polaritons, SPP). SPP predstavljaju hibridne ekscitacije nastale sprezanjem elektromagnetnih talasa sa oscilacijama slobodnih nosilaca naelektrisanja na razdvojnim površima izmeðu dva materijala sa razlicitim znakovima relativne dielektricne permitivnosti, npr. provodnika i dielektrika. Posledica ovakvog sprezanja je izmeðu ostalog lokalizacija elektromagnetnog zracenja na podtalasnom nivou, osobina plazmonskih struktura koja je našla veliku primenu u spektroskopiji, integrisanoj optici, senzorici itd. Jedna od znacajnih primena plazmonske lokalizacije je u oblasti u fotodetekcije, pre svega za poboljšanje performansi solarnih celija. Najveci problem proširenja primene plazmonike u fotodetekciji na drugu oblast od interesa, infracrvene (IC) detektore, predstavlja cinjenica da je plazmonska ucestanost vecine provodnika (metala) u ultraljubicastom ili vidljivom delu spektra. Brojne tehnološki pogodne tehnike koje su dale izuzetne rezultate za poboljšanje solarnih celija ostale su zbog toga bez primene u IC oblasti. Ova disertacija se prevashodno bavi proširenjem primenljivosti plazmonike na srednjetalasnu i dugotalasnu infracrvenu oblast i metodama prevazilaženja ogranicenja koje postavljaju sami materijali. U tu svrhu razmatrana su dva pristupa. Jedan od njih podrazumeva upotrebu submikrometarskih cestica od provodnog materijala. Funkcionalnost u IC oblasti postiže se kombinacijom izbora pogodnijeg materijala cestica (elektroprovodni opticki providni oksid umesto metala) i imerzije cestica u dielektrik visokog indeksa prelamanja. Drugi pristup podrazumeva korišcenje tankih metalnih slojeva sa ureðenom matricom apertura koji omogucuju pomeranje spektralne zavisnosti prema crvenom delu spektra menjanjem iskljucivo geometrijskih parametara matrice apertura. Oba pristupa nude mogucnost prakticno proizvoljnog podešavanja frekvencije plazmonske rezonancije i time njenu upotrebu za IC detektore. Analiza ova dva pristupa raðena je numerickim simulacijama, primenom metode konacnih elemenata. Uticaj na performanse infracrvenih detektora odreðivan je kombinovanjem rezultata numerickih modelovanja sa analitickim modelom IC detektora...

Plasmonics is one of the fastest growing fields in the contemporary science. Plasmonics studies properties of nanocomposite metamaterials which support surface plasmon polariton (SPP) resonance. SPP are formed by coupling electromagnetic waves with free charge carrier oscillations at an interface between materials with different signs of their relative permittivity i.e. conductor and dielectric. One of the results of this coupling is localization of electromagnetic radiation on subwavelength scale, property of plasmonic structures that has found practical use in the fields of spectroscopy, integrated optics, sensors, etc. One of the principal applications of light localization is in the field of photodetection, primarily for the enhancement of solar cells. The main problem with any attempt to apply plasmonics for photodetector enhancement at longer wavelengths, i.e. for infrared (IR) detectors, is that the plasmon resonance frequency of most conductive materials (metals) is in the ultraviolet or visible part of the spectrum. Because of this many convenient methods yielding excellent results for plasmonic enhancement of solar cells have not been utilized in the infrared. The main goal of this dissertation is bringing plasmonic enhancement of semiconductor photodetectors to medium and long wavelength infrared parts of the spectrum by overcoming limitations imposed by material properties. To achieve this two approaches are considered and analyzed. The first approach implies the use of submicrometer conductive particles. A sufficient shift of plasmonic resonance to the infrared is achieved by both a suitable choice of the particle material (transparent conductive oxides – TCO instead of metal) and by immersion of the particles in dielectric with a large index of refraction. The second approach is based on using thin metallic films with 2D array of holes drilled through them, where redshifting is achieved by tuning the geometrical properties of the hole array. It is shown that both approaches allow one to achieve practically arbitrary positioning of plasmonic resonance in the infrared. The finite element method was used for numerical simulations of the analyzed structures. A combination of the results of numerical modeling with the analytical results for the IR detectors was used to determine the effects of the plasmonic enhancement...