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Highly photoconductive oxide films functionalized with GeSi nanoparticles

Highly photoconductive oxide films functionalized with GeSi nanoparticles


Title: Highly photoconductive oxide films functionalized with GeSi nanoparticles
Author: Sultan, Muhammad Taha
Advisor: Halldór Guðfinnur Svavarsson
Date: 2019-11-27
Language: English
University/Institute: Reykjavik University
Háskólinn í Reykjavík (HR)
School: School of Technology (RU)
Tæknisvið (HR)
Department: Department of Applied Engineering (RU)
Iðn- og tæknifræðideild (HR)
Subject: Photoconductivity; Physics; Nanotechnology; Semiconductors; Sensors; Eðlisfræði; Ljósfræði; Nanótækni; Hálfleiðarar
URI: https://hdl.handle.net/20.500.11815/1766

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Abstract:

 
Growth of self-assembled quantum dots is of great interest due to their potential quantum confinement effect and numerous applications in optoelectronics and nano-sized structures. Semiconducting Si, Ge and SiGe nanocrystals (NCs), embedded in a dielectric-oxide matrix have for instance been found to exhibit strong quantum confinement. For SiGe nano-based structures in addition to strong quantum confinement effect they offer the advantage of fine tuneability of energy-band structure via quantum confinement, strain engineering and varying the Si/Ge ratio. Among the most common methods to obtain NCs embedded in oxide systems is deposition with magnetron sputtering, followed by subsequent anneal treatments. However, the device performance obtained are lower in production line than obtained for research devices. This has mainly been attributed to the thermal treatment used, which causes strain accumulation within the structure, dislocations and dangling bonds, clustering and phase separation of Ge in Si1-xGex system, diffusion and formation of unwanted insulating oxide. All of these side-effects cause degradation of optical and electrical properties of the fabricated structures. In this study, structures comprising of SiO2/SiGe/SiO2 and TiO2/SiGe/TiO2 were fabricated by utilizing radio frequency (rfMS), direct current (dcMS) and/or high power impulse magnetron sputtering (HiPIMS). The structures were then subjected to thermal and/or hydrogen (H2) plasma treatment. Their photocurrent intensity was increased by up to several orders of magnitude along with wider spectral coverage into near infra-red regime by controlling the sputter discharge and anneal parameters. Moreover, as a proof of concept, a control over the HiPIMS discharge parameters have exhibited the possibility of obtaining as-grown crystalline structures, consisting of SiGe NCs without the need of annealing, along with a viable control over the size of NCs. The annealing of such structure prepared via HiPIMS method, have shown an interesting self-organization of periodically arranged columnar SiGe NCs. Exposure to hydrogen plasma of both as-grown samples and annealed samples ensued amplification in photoconductivity by neutralization of dangling bonds and passivation of non-radiative defects in the oxide matrix and/or at SiGe/matrix interfaces.
 
Ræktun sjálfsamsettra skammtapunkta er mjög áhugavert rannsóknaverkefni vegna margvíslegra notkunarmöguleika í ljósnæmum rafeindatækjum og ýmsum örsmáum skynjurum. Hálfleiðandi Si, Ge og SiGe öragnir í þunnhúðum úr torleiðiefnum (einkum málmoxíðum) hafa til dæmis reynst hafa sterka skammtaeiginleika. Sökum skammtahrifa má fínstilla þá ljós-öldulengd sem þarf til að gera þá leiðandi með því að stýra stærð öragnanna, hlutfalli milli Si og Ge og álagi sem þeir verða fyrir í þunnhúðinni. Algengasta leiðin til að búa til ofangreind kerfi er þunnhúðun með segulspætun og hitameðhöndlun í kjölfarið. Hefðbundin hitameðferð veldur hinsvegar ákveðnum skemmdum í Si1-xGex kerfinu, s.s. lausum efnatengjum, efnis-aðskilnaði, myndun þyrpinga og útsveimi. Þessar aukaverkanir rýra ljós- og rafeiginleika efnisins. Framleiðslu aðferðir sem valda ekki slíkum skemmdum geta því haft mikla þýðingu. Í þessari rannsókn voru riðspennu (rfMS)-, jafnspennu (dcMS) - og háaflpúlsuð segulspætun (HiPIMS) aðferðir notaðar til að rækta lög af SiO2/SiGe/SiO2 og TiO2/SiGe/TiO2 kerfum. Í kjölfarið var mildum hita- og vetnis rafgasmeðferðum beitt til að framkalla SiGe og Ge öragnir í húðinni sem sýndu breytilega ljósnæmni. Með þessum hætti tókst að auka ljósnæmnina um nokkrar stærðargráður auk þess sem næmnisvið litrófsins var víkkað. Önnur megin niðurstaða er að með notkun HiPIMS aðferðarinnar tóks að útbúa sýni með háa ljósnæmni án þess að hitameðhöndla þau. Meðhöndlun með vetnis-rafgasi leiddi til mikillar (stærðargráðu) aukningar á ljósnæmni húðanna, bæði fyrir og eftir hitaneðhöndlun.
 

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