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Author:Lehtola, Lauri
Title:Epitaxial overgrowth of nanopillar patterned gallium nitride
Publication type:Master's thesis
Publication year:2013
Pages:[6] + 57      Language:   eng
Department/School:Teknillisen fysiikan laitos
Main subject:Optiikka ja molekyylimateriaalit   (Tfy-125)
Supervisor:Kaivola, Matti
Instructor:Sopanen, Markku ; Nagarajan, S.
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  161   | Archive
Keywords:gallium nitride
nanopillar
MOVPE
nickel mask
galliumnitridi
nanopilari
MOVPE
nikkelimaski
Abstract (eng): In this Master's thesis work the fabrication of gallium nitride (GaN) nanopillars and their overgrowth with metal-organic vapor phase epitaxy (MOVPE) was investigated.

In addition, a quantum well structure capable of emitting light was grown on top of the nanopillars.
The structural properties of the nanopillars were studied using scanning electron microscopy, and the optical properties of the quantum well structures were examined using photoluminescence measurements.
The research was carried out in Optoelectronics research group at the department of Micro and Nanosciences, Aalto School of Electrical Engineering.

The GaN nanopillar templates were fabricated by inductively-coupled plasma (ICP) etching using self-assembling nickel nanoisland masks.
The method is suitable for patterning a whole 2" wafer.
The nanoisland diameter can be controlled with the nickel layer thickness.

Thin layers of GaN were grown on top of the nanopillar templates in various growth conditions using MOVPE.
The combination of intermediate temperature and V/III ratio with low pressure yielded in hexagonal nanopillars with smooth surfaces.
The size of inclined planes between the top and side walls could be controlled up to some point by varying the growth conditions.

In the final step a quantum well structure was grown on top of a nanopillar template.
When the quantum wells were excited using a 325 nm laser they were observed to emit at the wavelengths of 375 nm, 475 nm and 490 nm.
Abstract (fin): Tässä diplomityössä tutkittiin nanopilareiden valmistusta galliumnitridistä (GaN) ja näiden nanopilareiden uudelleenkasvatusta metallo-orgaanisella kaasufaasiepitaksialla (MOVPE).
Osana työtä nanopilareiden päälle kasvatettiin kvanttikaivorakenne, joka viritettäessä emittoi valoa.
Nanopilareita tutkittiin pyyhkäisyelektronimikroskoopilla, ja kvanttikaivorakenteiden optisia ominaisuuksia selvitettiin fotoluminesenssimittauksin.
Diplomityö tehtiin Optoelektroniikan tutkimusryhmässä, Mikro- ja nanotekniikan laitoksessa, Aalto-yliopiston sähkötekniikan korkeakoulussa.

Galliumnitridinanopilarit valmistettiin induktiivisesti kytketyllä plasmaetsauksella (ICP) käyttämällä itse järjestyviä nikkelimaskeja.
Menetelmä sopii hyvin kokonaisten kahden tuuman kiekkojen kuviointiin.
Maskin muodostavien nanosaarekkeiden kokoon voidaan vaikuttaa muuttamalla nikkelikerroksen paksuutta.

Etsattujen nanopilareiden päälle kasvatettiin ohuita GaN-kerroksia MOVPE menetelmällä erilaisissa kasvuolosuhteissa.
Alhainen paine sekä keskisuuret lämpötila ja V/III-prekursoreiden suhde tuottivat kuusikulmaisia nanopilareita, joiden pinnat olivat hyvin sileitä.
Nanopilareiden pystyseinämien ja päätyjen väliin muodostuvan kallistuneen pinnan kokoa pystyttiin kontrolloimaan kasvuolosuhteita muuttamalla.

Työn viimeisessä vaiheessa nanopilareiden päälle kasvatettiin kvanttikaivorakenne.
Kun kvanttikaivoja viritettiin 325 nm laserilla, ne emittoivat valoa 385 nm:n, 457 nm:n ja 490 nm:n aallonpituuksilla.
ED:2013-09-05
INSSI record number: 47167
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