25 research outputs found
Terminen ja plasma-avusteinen atomikerroskasvatus: tutkimus ja käyttö moninaisiin nanoteknologian sovelluksiin
No full textThis thesis focuses on atomic layer deposition (ALD) and presents results divided between two parts. The first part examines plasma-enhanced atomic layer deposition (PEALD) of AlN and the effects processing conditions have on material properties and growth. The second part focuses on the employment of various ALD thin films for diverse nanotechnology applications.
For PEALD AlN films deposited using a capacitively coupled plasma source it was demonstrated that the choice of plasma gas, processing temperature, and plasma bias voltage have a marked effect on the growth and physical properties. PEALD AlN was further investigated as a dry etch mask for SF6-based silicon plasma etching. Experiments using inductively coupled plasma-reactive ion etch and reactive ion etch systems show the material to be an excellent hard mask, akin to ALD Al2O3. A surface stack consisting of PEALD AlN and ALD HfO2 was deposited on GaAs to form high-k metal insulator semiconductor capacitors. Surface passiv-ation of GaAs by PEALD AlN was established by showing Fermi level unpinning at the interface using capacitance-voltage and current-voltage measurements.
ALD Al-doped ZnO (AZO) was investigated as a platform for GaAs nanowire (NW) growth on a variety of materials not normally conducive to NW growth. The GaAs NWs were uniform irrespective of the underlying substrate. Photoluminescence measurements indicate the NWs incorporated Zn from AZO and illuminated even at room temperature. ALD TiO2 and Al2O3 were studied as intermediary layers between ZnO nanorods (ZnOr) and a porphyrin based organic layer. Fluorescence measurements indicate that a 5 nm-thick Al2O3 layer allows the study of the organic layer alone by isolating it from the ZnOr. A 5 nm-thick TiO2 however results in an interaction between the organic layer and ZnOr layer. Femtosecond absorption spectroscopy revealed that a 5 nm-thick TiO2 shell enables charge separation to occur between the organic and semiconductor materials. Dye sensitized solar cell experiments further validate that this TiO2 shell decreases charge recombination.
A new type of graphene-alumina composite membrane was developed and mechanically assessed using the bulge test. The composite membrane is significantly more robust than plain Al2O3, withstanding at least 3 times more differential pressure. Raman measurements indicated the graphene reinforcing layer remains undamaged after bulge testing despite cracking in the ALD layer.Tässä väitöskirjassa käsiteltiin atomikerroskasvatusta (engl. ALD) ja sen tulokset esitetään jaettuna kahteen osaan. Ensimmäisessä osassa käsitellään AlN:n plasma-avusteista atomikerroskasvatusta (engl. PEALD) ja esitetään havaintoja sen prosessiolosuhteiden vaikutuksesta materiaalin ominaisuuksiin ja kasvuun. Toisessa osassa käsitellään erilaisten ALD-ohutkalvojen käyttämistä osana erilaisia nanoteknologian sovelluksia.
PEALD AlN-ohutkalvoja valmistettiin käyttämällä kapasitiivisesti kytkettyä plasmalähdettä. Tutkimukset osoittivat plasmakaasun, prosessilämpötilan ja plasman tasajännitteen vaikuttavan ohutkalvojen kasvuun ja fysikaalisiin ominaisuuksiin. Tämän lisäksi PEALD AlN:ä tutkittiin kuivaetsausmaskina SF6-pohjaiselle piin plasmaetsaukselle. Induktiivisesti kytkettyä plasma-reaktiivista sekä reaktiivista ionietsausta käyttäen tehdyt kokeet osoittivat materiaalin olevan erinomainen kovamaski, samoin kuin Al2O3. Myös korkean permittiivisyyden omaavia metallieriste-puolijohdekondensaattoreita valmistettiin GaAs alustalle PEALD AlN ja ALD HfO2-kerrosrakenteilla. GaAs-pinnan passivointi saavutettiin PEALD AlN:llä todentamalla rajapinnan Fermi tason irtoaminen käyttäen kapasitanssi-jännite ja virta-jännite -mittauksia.
ALD Al-seostettua ZnO:a (AZO) tutkittiin GaAs-nanolankojen kasvualustana moninaisille materiaaleille jotka eivät normaalisti tue nanolankojen kasvua. Tuotetut GaAs-nanolangat olivat tasalaatuisia riippumatta alustasubstraatista. Fotoluminesenssimittaukset osoittivat AZO:sta peräisin olevan sinkin olevan osa nanolankoja, jotka emittoivat valoa jopa huoneen lämpötilassa. Jatkotutkimuksessa ALD TiO2:a ja Al2O3:a käytettiin ZnO-nanosauvojen ja porfyriinipohjaisen orgaanisen kerroksen välikerroksena. Fluoresenssimittaukset osoittivat 5 nm paksun Al2O3-kerroksen eristävän ZnO-nanosauvat orgaanisesta kerroksesta, tehden sen tutkimisen mahdolliseksi. 5 nm paksu TiO2 sen sijaan johti vuorovaikutukseen orgaanisen ja ZnO-nanosauvakerroksen välillä. Femtosekunti-absorptio-spektroskopia paljasti 5 nm paksun TiO2-kuoren mahdollistavan varauserotuksen orgaanisen ja puolijohdemateriaalin välillä. Väriaineherkistetyt aurinkokennokokeet vahvistivat tulokset että TiO2-kuori todella vähentää varausrekombinaatiota.
Osana tätä työtä kehitettiin myös uuden tyyppinen grafeeni-alumiinioksidi komposiittimembraani ja sitä arvioitiin mekaanisesti aluevenymäkoejärjestelmällä. Komposiittimembraanin todettiin olevan huomattavasti kestävämpi kuin pelkkä Al2O3 olisi, kestäen jopa kolme kertaa suuremman differentiaalisen paineen. Ramanmittaukset osoittivat vahvistavan grafeeni-kerroksen pysyvän vahingoittumattomana aluevenymäkokeen jälkeen, vaikka ALD-kerroksessa havaittiin säröytymistä
Wide-Band Black Silicon with Atomic Layer Deposited NbN
No full textTarkista embargo, kun artikkeli julkaistu.Antireflection surfaces are often utilized in optical components to reduce undesired reflection and increase absorption. We report on black silicon (b-Si) with dramatically enhanced absorption over a broad wavelength range (250– 2500 nm) achieved by applying a 10–15 nm conformal coating of NbN with atomic layer deposition (ALD). The improvement is especially pronounced in the near infrared (NIR) range of 1100– 2500 nm where absorption is increased by >90%. A significant increase of absorption is also observed over the ultraviolet (UV) range of 200–400 nm. Preceding NbN deposition with a nanostructured ALD Al2O3 (n-Al2O3) coating to enhance the NbN texture was also examined. Such texturing further improves absorption in the NIR, especially at longer wavelengths, strong absorption up to 4–5 μm wavelengths has been attested. For comparison, double side polished silicon and sapphire coated with 10 nm-thick NbN exhibited absorption of only ~55% in the NIR range of 1100–2500 nm. The results suggest a positive correlation between the surface area of NbN coating and optical absorption. Based on the wide-band absorption, the presented NbN-coated b-Si may be an attractive candidate for use in e.g. spectroscopic systems, infrared microbolometers.Peer reviewe
Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films
No full textPlasma-enhanced atomic layer deposition was utilized to grow aluminum nitride (AlN) films on Si from trimethylaluminum and N2:H2 plasma at 200 °C. Thermal treatments were then applied on the films which caused changes in their chemical composition and nanostructure. These changes were observed to manifest in the refractive indices and densities of the films. The AlN films were identified to contain light element impurities, namely, H, C, and excess N due to nonideal precursor reactions. Oxygen contamination was also identified in the films. Many of the embedded impurities became volatile in the elevated annealing temperatures. Most notably, high amounts of H were observed to desorb from the AlN films. Furthermore, dinitrogen triple bonds were identified with infrared spectroscopy in the films. The triple bonds broke after annealing at 1000 °C for 1 h which likely caused enhanced hydrolysis of the films. The nanostructure of the films was identified to be amorphous in the as-deposited state and to become nanocrystalline after 1 h of annealing at 1000 °C.peerReviewe
Scalable graphene electro-optical modulators for all-fibre pulsed lasers
No full textPublisher Copyright: © The Royal Society of Chemistry.Recently, graphene electro-optical modulators have emerged as a viable alternative to the conventional modulators due to their broadband operation, ultrafast responsivity, small footprint, and low energy consumption. Here, we report scalable graphene electro-optical modulators for all-fibre pulsed laser applications. An actively Q-switched all-fibre laser is demonstrated with a scalable graphene electro-optical modulator for the first time, which is different from the previously reported work that typically implemented graphene electro-optical modulators in a free-space optical system. Our electrically modulated actively Q-switched fibre laser outputs at the centre wavelength of ~1961.9 nm, the tunable repetition rate of 56.5 to 62.5 kHz, the maximum pulse energy of ~80 nJ, and the signal-to-noise ratio of ~46.6 dB. This work demonstrates that the scalable all-fibre integrated graphene electro-optical modulator approach is promising for producing pulsed fibre lasers at 2 µm with high performance and easy integration which are useful in various applications such as medical treatment, material processing, and spectroscopy. This journal isPeer reviewe
Hybrid GaAs nanowire-polymer device on glass: Al-doped ZnO (AZO) as transparent conductive oxide for nanowire based photovoltaic applications
No full textAl-doped ZnO (AZO) is pursued as an alternative low-cost transparent conductive oxide (TCO) to expensive ITO. Atomic layer deposition grown AZO films showing resistivity of 5 x 10-3 Ωcm and transmittance > 85% in the visible region are reported. Au-assisted GaAs nanowires are grown directly on an optimized AZO coated glass and a GaAs nanowire-polymer hybrid device on glass is demonstrated which confirms that the as-grown GaAs nanowires form a perfect ohmic contact to AZO film. The device shows that AZO can be used as transparent electrode as well as low-cost growth platform for GaAs NWs. Finally, a simple device idea is proposed to fabricate optically transparent GaAs nanowire based solar cells on low-cost glass.Peer reviewe
Low temperature and high quality atomic layer deposition HfO<inf>2</inf> coatings
No full textComparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films
No full textA comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110), and Al (111) oriented substrates to study the effect of substrate texture on film properties. For the PEALD trimethylaluminum–ammonia films, the effects of process parameters, such as temperature, bias voltage, and plasma gas (ammonia versus N2/H2), on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81–0.90. The mass densities were ∼3.10 and ∼2.70 g/cm3 for sputtered and PEALD AlN, respectively. The sputtered films were found to have higher degrees of preferential crystallinity, whereas the PEALD films were more polycrystalline as determined by x-ray diffraction. Nanoindentation experiments showed the elastic modulus and hardness to be 250 and 22 GPa, respectively, for sputtered AlN on the (110) substrate, whereas with PEALD AlN, values of 180 and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61–421 MPa), whereas the PEALD films had a residual stress ranging from tensile to compressive (846 to −47 MPa), and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behavior. Also, the substrate underneath the sputtered AlN did not withstand high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ∼0.2 for both AlN types, and their wear characteristics were almost identical.peerReviewe
Atomic Layer Engineering of Er-Ion Distribution in Highly Doped Er:Al<sub>2</sub>O<sub>3</sub> for Photoluminescence Enhancement
No full textFor the past decade, erbium-doped integrated waveguide amplifiers and lasers have shown excellent potential for on-chip amplification and generation of light at the important telecommunication wavelength regime. However, Er-based integrated devices can only provide small gain per unit length due to the severe energy-transfer between the Er-ions at high concentration levels. Therefore, active ion concentrations have been limited to <1% levels in these devices for optimal performance. Here, we show an efficient and practical way of fabricating Er-doped Al2O3 with Er-concentration as high as ∼3.5% before concentration quenching starts to limit the C-band emission in our material. The Er-doped Al2O3 was fabricated by engineering the distribution of the Er-ions in Al2O3 with the atomic layer deposition (ALD) technique. By choosing a proper precursor for the fabrication of Er2O3, the steric hindrance effect was utilized to increase the distance between the Er-ions in the lateral direction. In the vertical direction, the distance was controlled by introducing subsequent Al2O3 layers between Er2O3 layers. This atomic scale control of the Er-ion distribution allows us to enhance the photoluminescence of our Er:Al2O3 material by up to 16 times stronger when compared to the case where the Er-concentration is ∼0.6%. In addition, long lifetime of approximately 5 ms is preserved in the Er-ions even at such high concentration levels. Thus, our optimized ALD process shows very promising potential for the deposition of optical gain media for integrated photonics structures.</p
