Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors have different applications in sensors and fiber optic communication systems, and medical diagnosis etc. In this project  Fourier Transform Infrared (FTIR) Spectroscopy is used to investigate a new version  of photodiodes for near-infrared radiation that is based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied, respectively. The thesis work also includes a comparison to a planar photodetector based on Indium Tin Oxide (ITO) deposited directly on an InP substrate.

This thesis describes the fabrication and testing of electroluminescent diodes made from silicon subjected to plasma ion implantation. A silicon-compatible, electrically driven light source is desired to increase the speed and efficiency of short-range data transfer in the communications and computing industries. As it is an indirect band gap material, ordinary silicon is too inefficient a light source to be useful for these applications. Past experiments have demonstrated that modifying the structural properties of the crystal can enhance its luminescence properties, and that light ion implantation is capable of achieving this effect. This research investigates the relationship between the ion implantation processing parameters, the post-implantation annealing temperature, and the observable electroluminescence from the resulting silicon diodes.<p> Prior to the creation of electroluminescent devices, much work was done to improve the efficiency and reliability of the fabrication procedure. A numerical algorithm was devised to analyze Langmuir probe data in order to improve estimates of implanted ion fluence. A new sweeping power supply to drive current to the probe was designed, built, and tested. A custom software package was developed to improve the speed and reliability of plasma ion implantation experiments, and another piece of software was made to facilitate the viewing and analysis of spectra measured from the finished silicon LEDs.<p> Several dozen silicon diodes were produced from wafers implanted with hydrogen, helium, and deuterium, using a variety of implanted ion doses and post-implantation annealing conditions. One additional device was fabricated out of unimplanted, unannealed silicon. Most devices, including the unimplanted device, were electroluminescent at visible wavelengths to some degree. The intensity and spectrum of light emission from each device were measured. The results suggest that the observed luminescence originated from the native oxide layer on the surface of the ion-implanted silicon, but that the intensity of luminescence could be enhanced with a carefully chosen ion implantation and annealing procedure.</p>

<p>The purpose of this thesis work is to design and fabricates organic-inorganic hetero junction White Light Emitting Diode (WLED). In this WLED, inorganic material is n- type ZnO and organic material is p-type conjugated polymer. The first task was to synthesise vertically aligned ZnO nano-rods on glass as well as on plastic substrates using aqueous chemical growth method at a low temperature. The second task was to find out the proper p- type organic material that gives cheap and high efficient WLED operation. The proposed polymer shouldn’t create a high barrier potential across the interface and also it should block electrons entering into the polymer. To optimize the efficiency of WLED; charge injection, charge transport and charge recombination must be considered. The hetero junction organic-inorganic structures have to be engineered very carefully in order to obtain the desired light emission. The layered structure is composed of p-polymer/n-ZnO and the recombination has been desired to occur at the ZnO layer in order to obtain white light emission. Electrical characterization of the devices was carried out to test the rectifying properties of the hetero junction diodes.</p><p>iv</p>

One-dimensional ZnO nanostructures have great potential applications in the fields of optoelectronic and sensor devices.  Therefore, it is very important to realize the controllable growth of one-dimensional ZnO nanostructures and investigate their properties. The main points for this thesis are not only to successfully realize the controllable growth of ZnO nanorods (ZNRs), ZnO nanotubes (ZNTs) and ZnMgO/ZnO heterostructures, but also investigate the structure and optical properties in detail by means of scanning electron microscope (SEM), transmission electron microscope (TEM), resonant Raman spectroscopy (RRS), photoluminescence (PL), time resolved PL (TRPL), X-ray photoelectron spectroscopy (XPS) and Secondary ion mass spectrometry (SIMS). For ZNRs, on one hand, ZNRs have been successfully synthesized by a two-step chemical bath deposition method on Si substrates. The diameter of ZNRs can be well controlled from 150 nm to 40 nm through adjusting the diameter and density of the ZnO nanoparticles pretreated on the Si substrates. The experimental results indicated that both diameter and density of ZnO nanoparticles on the substrates determined the diameter of ZNRs. But when the density is higher than the critical value of 2.3×108cm-2, the density will become the dominant factor to determine the diameter of ZNRs. One the other hand, the surface recombination of ZNRs has been investigated in detail. Raman, RRS and PL results help us reveal that the surface defects play a significant role in the as-grown sample. It is the first time to the best of our knowledge that the Raman measurements can be used to monitor the change of surface defects and deep level defects in the CBD grown ZNRs. Then we utilized TRPL technique, for the first time, to investigate the CBD grown ZNRs with different diameters. The results show that the decay time of the excitons in ZNRs strongly depends on the diameter. The altered decay time is mainly due to the surface recombination process. A thermal treatment under 500°C can strongly suppress the surface recombination channel. A simple carrier and exciton diffusion equation is also used to determine the surface recombination velocity, which results in a value between 1.5 and 4.5 nm/ps. Subsequently, we utilized XPS technique to investigate the surface composition of as-grown and annealed ZNRs so that we can identify the surface recombination centers. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Finally, on the basis of results above, we explored an effective way, i.e. sealing the beaker during the growth process, to effectively suppress the surface recombination of ZNRs and the suppression effect is even better than a 500oC post-thermal treatment. For ZNTs, the structural and optical properties have been studied in detail. ZNTs have been successfully evolved from ZNRs by a simple chemical etching process. Both temperature-dependent PL and TRPL results not only further testify the coexistence of spatially indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their strong enhancement of luminescence intensity. For ZnMgO/ZnO heterostructures, the Zn0.94Mg0.06O/ZnO heterostructures have been deposited on 2 inch sapphire wafer by metal organic chemical vapor deposition (MOCVD) equipment. PL mapping demonstrates that Mg distribution in the entire wafer is quite uniform with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors in Zn0.94Mg0.06O/ZnO heterostructures have been investigated by SIMS in detail. All the SIMS depth profiles of Mg element have been fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC is two orders of magnitude lower than that of annealing samples, which clearly testifies that the deposited temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells. This thesis not only provides the effective way to fabricate ZNRs, ZNTs and ZnMgO/ZnO heterostructures, but also obtains some beneficial results in aspects of their optical properties, which builds theoretical and experimental foundation for much better understanding fundamental physics and broader applications of low-dimensional ZnO and related structures. / Endimensionella nanostrukturer av ZnO har stora potentiella tillämpningar för optoelektroniska komponenter och sensorer. Huvudresultaten för denna avhandling är inte bara att vi framgångsrikt har realiserat med en kontrollerbar metod ZnO nanotrådar (ZNRs), ZnO nanotuber (ZNTs) och ZnMgO/ZnO heterostrukturer, utan vi har också undersökt deras struktur och optiska egenskaper i detalj. För ZNRs har diametern blivit välkontrollerad från 150 nm  ner till 40 nm. Den storlekskontrollerande mekanismen är i huvudsak relaterad till tätheten av ZnO partiklarna som är fördeponerade på substratet. De optiska mätningarna ger upplysning om att ytrekombinationsprocessen spelar en betydande roll för tillväxten av ZNR. En värmebehandling i efterhand  vid 500 grader Celsius eller användande av en förseglad glasbägare under tillväxtprocessen kan starkt hålla nere kanalerna för ytrekombinationen.För ZNT, dokumenterar vi inte bara samexistensen av rumsliga indirekta och direkta  övergångar på grund av bandböjning, men vi konstaterar också att vi har mindre icke-strålande bidrag till den optiska emissionsprocessen i ZNT. För ZnMgO/ZnO heterostrukturer konstaterar vi med hjälp av analys av Mg diffusionen i den växta och den i efterhand uppvärmda Zn(0.94)Mg(0.06)O filmen, att en tillväxt vid 700 grader Celsius är den mest lämpliga för att växa ZnMgO/ZnO heterostrukturer eller kvantbrunnar.   Denna avhandling ger en teoretisk och experimentell grund för bättre förståelse av grundläggande fysik och för tillämpningar av lågdimensionella strukturer. / SSF, VR

Die vorliegende Arbeit befasst sich mit dem vertieften Verständnis der Rekombinationsdynamik von polaren ZnO/MgZnO-Quantengraben(QW)-Strukturen zur exakten Bestimmung des unabgeschirmten Grundzustandes und der Analyse der zugrundeliegenden Emissionsprozesse. Dafür werden ausgehend von Beobachtungen an ZnO-Dünnschichten die Eigenschaften von mittels PLD hergestellten QWs unter dem Einfluss des internen elektrischen Feldes mit Hilfe der zeitintegrierten (TI-) und zeitaufgelösten (TR-) Photolumineszenz(PL)-Spektroskopie untersucht. Die Differenz der spontanen und piezoelektrischen Polarisation zwischen ZnO und MgZnO führt zur Ausbildung eines internen elektrischen Feldes und damit zum Auftreten des quantum-confined Stark effect (QCSE). Es wird gezeigt, dass der QCSE durch eine Durchmischung der Grenzflächen stark vermindert wird. Für QWs mit schwachem QCSE ist die Übergangsenergie und Zerfallszeit des Grundzustandes experimentell gut bestimmbar. Bei starkem QCSE müssen jedoch bereits bei geringen Anregungsdichten (1E10 /cm²) Abschirmeffekte berücksichtigt werden. Dadurch ist es sehr schwierig, den unabgeschirmten Grundzustand mittels herkömmlicher experimenteller Methoden mit einem aussagekräftigen Signal-Rausch-Verhältnis zu bestimmen. Es wird gezeigt, dass für QWs mit einer Dicke > 4 nm die Übergangsenergie des unabgeschirmten Grundzustandes nicht durch TI-PL-Messungen bestimmt werden kann. TR-PL-Messungen zeigen energetisch tiefere Übergangsenergien, jedoch ebenfalls nicht den unabgeschirmten Grundzustand. Mit einem eingeführten Modell zur Beschreibung der zeitabhängigen Abschirmung des Grundzustandsniveaus wird die Zerfallszeit für QW-Dicken in einem Bereich von 1 - 10 nm bestimmt. Durch die selbstkonsistente Lösung von Schrödinger- und Poissongleichung werden die Übergangsenergie und Zerfallszeit der Exzitonen im QW in Abhängigkeit der Feldstärke und auch der Ladungsträgerdichte berechnet. Dadurch ist eine exaktere Bestimmung der Feldstärke möglich. Zusätzlich wird durch die vergleichende Untersuchung von QWs unterschiedlicher Dicke, Potentialhöhe und Wachstumsunterlage die spontane und piezoelektrische Polarisation der Materialien experimentell bestimmt. Mittels temperaturabhängiger Messungen wird der Ursprung der Lumineszenz für QW-Dicken > 2 nm der Rekombination freier Exzitonen im QW zugeschrieben. Für dünnere QWs ist der temperaturabhängige Verlauf des PL-Maximums durch Lokalisation der Exzitonen bestimmt.

In der vorliegenden Arbeit werden ZnO-Mikronadeln bezüglich ihrer Anwendbarkeit als Mikroresonatoren untersucht. Dabei stehen Kavitätsmoden im Fokus der Untersuchungen, die sich nur senkrecht zur Nadelachse ausbreiten, sprich innerhalb der hexagonalen Nadelquerschnittsfläche. Folglich wird der Einfluss der Gestalt der Querschnittsfläche auf Resonatoreigenschaften wie Propagation, Form, Direktionalität und Qualität der Kavitätsmoden sowohl theoretisch simuliert als auch experimentell nachgewiesen. Die dabei beobachteten hohen Qualitätsfaktoren von Flüstergalerie-Moden ermöglichen es darüberhinaus, Wechselwirkungseffekte zwischen Kavität und Mode zu beobachten. Der erste Teil der Arbeit beschäftigt sich mit der regulären, polygonalen Resonatorform und deren Einfluss auf die Dimensionalität von Kavitätsmoden sowie deren mögliche Wechselwirkung mit dem elektronischen System des Resonators. Beispielhaft wird ein hexagonaler Resonator zur Veranschaulichung gewählt, wie er durch ZnO-Mikronadeln gegeben ist, undmittels Finite-Difference-Time-Domain (FDTD)-Simulationen sowie winkelaufgelöster Photolumineszenz (PL)-Spektroskopie untersucht. Die aufgenommenen PL-Spektren können unter Zuhilfenahme photonischer Dispersionskurven von ein- und zwei-dimensionalen Kavitätsmoden reproduziert werden. Basierend auf diesen Ergebnissen wird der Einfluß der Resonatorecken auf die Lichtauskopplung diskutiert und mittels winkelaufgelöster, anregungsabhängiger und temperaturabhängier PL-Spektroskopie nachgewiesen. Desweiteren wird auf die Wechselwirkung zwischen dem Resonator und den Kavitätsmoden eingegangen, imSpeziellen auf die starke Kopplung zwischen Flüstergalerie-Moden und freien Exzitonen imResonatormaterial. Bereits erschienende Publikationen zu diesemThema werden präsentiert und kritisch hinterfragt. Dabei wird ein Leitfaden aufgestellt, der eine Evaluierung möglicher Polaritonen-Phänomene ermöglicht. Um Wechselwirkungen dieser Art auch in den hier untersuchtenMikronadeln nachzuweisen, werden Hochanregungs-PL-Messungen durchgeführt. Dabei werden Messungen in der Mitte der Nadel sowie in der Nähe ihrer Ecken getätigt, um spezielle Polaritonen-Propagationseffekte beobachten zu können. Im zweiten Teil der Arbeit wird der Einfluß von irregulären und inhomogenen Resonatorformen auf die Bildung von Flüstergalerie-Moden diskutiert. Dafür werden elongierte Teile der Nadeln, die durch laterale Auswüchse entstehen, winkelaufgelöst bezüglich einer gerichteten Auskopplung von Kavitätsmoden vermessen und verzerrte Mikronadeln, wie sie beim Biegen entstehen, bezüglich der entstehenden Deformationseffekte und deren Einfluss auf die Kavitätsmoden mittels hochaufgelöster Mikro-PL untersucht. Die experimentellen Ergebnisse zu irregulären Resonatoren können durch FDTD-Simulationen bestätigt werden. Desweiteren wurden Mikronadel- und Nanonadel-Quantengraben-Heterostrukturen hergestellt und deren Lumineszenzeigenschaften diskutiert. Dabei wird speziell auf die Homogenität der Quantengrabenemission eingegangen und Strategien zur Realisierung einer starken Kopplung zwischen Flüstergalerie-Moden und Quantengraben-Exzitonen aufgestellt. Diese Strategien werden experimentell umgesetzt und deren Ergebnisse anhand von Kathodolumineszenzmessungen vorgestellt.

Heteroepitaxial SiGe(C) layers have attracted immense attention as a material for performance boost in state of the art electronic devices during recent years. Alloying silicon with germanium and carbon add exclusive opportunities for strain and bandgap engineering. This work presents details of epitaxial growth using chemical vapor deposition (CVD), material characterization and integration of SiGeC layers in MOS devices. Non-selective and selective epitaxial growth of Si1-x-yGexCy (0≤x≤0.30, 0≤y≤0.02) layers have been performed and optimized aimed for various metal oxide semiconductor field effect transistor (MOSFET) applications. A comprehensive experimental study was performed to investigate the growth of SiGeC layers. The incorporation of C into the SiGe matrix was shown to be strongly sensitive to the growth parameters. As a consequence, a much smaller epitaxial process window compared to SiGe epitaxy was obtained. Incorporation of high boron concentrations (up to 1×1021 atoms/cm3) in SiGe layers aimed for recessed and/or elevated source/drain (S/D) junctions in pMOSFETs was also studied. HCl was used as Si etchant in the CVD reactor to create the recesses which was followed (in a single run) by selective epitaxy of B-doped SiGe. The issue of pattern dependency behavior of selective epitaxial growth was studied in detail. It was shown that a complete removal of pattern dependency in selective SiGe growth using reduced pressure CVD is not likely. However, it was shown that the pattern dependency can be predicted since it is highly dependent on the local Si coverage of the substrate. The pattern dependency was most sensitive for Si coverage in the range 1-10%. In this range drastic changes in growth rate and composition was observed. The pattern dependency was explained by gas depletion inside the low velocity boundary layer. Ni silicide is commonly used to reduce access resistance in S/D and gate areas of MOSFET devices. Therefore, the effect of carbon and germanium on the formation of NiSiGe(C) was studied. An improved thermal stability of Ni silicide was obtained when C is present in the SiGe layer. Integration of SiGe(C) layers in various MOSFET devices was performed. In order to perform a relevant device research the dimensions of the investigated devices have to be in-line with the current technology nodes. A robust spacer gate technology was developed which enabled stable processing of transistors with gate lengths down to 45 nm. SiGe(C) channels in ultra thin body (UTB) silicon on insulator (SOI) MOSFETs, with excellent performance down to 100 nm gate length was demonstrated. The integration of C in the channel of a MOSFET is interesting for future generations of ultra scaled devices where issues such as short channel effects (SCE), temperature budget, dopant diffusion and mobility will be extremely critical. A clear performance enhancement was obtained for both SiGe and SiGeC channels, which point out the potential of SiGe or SiGeC materials for UTB SOI devices. Biaxially strained-Si (sSi) on SiGe virtual substrates (VS) as mobility boosters in nMOSFETs with gate length down to 80 nm was demonstrated. This concept was thoroughly investigated in terms of performance and leakage of the devices. In-situ doping of the relaxed SiGe was shown to be superior over implantation to suppress the junction leakage. A high channel doping could effectively suppress the source to drain leakage. / <p>QC 20100715</p>

The first part of this thesis deals with the study of mesoscopic fluctuations of the Coulomb drag resistance in double-layer GaAs/AlGaAs heterostructures, both in weak magnetic fields and strong magnetic fields. In the second part, measurements are made in a monolayer graphene structure, specifically of the quantum lifetime, and the mesoscopic resistance fluctuations at quantising magnetic fields.

With  the  continuous  advances  in  microwave  technology,  microwave  components  and  related magnetic materials become more important in industrial environment. In order to further develop the microwave components, it is of interest to find new kinds of technologies and materials. Here, we  introduce  a  new  kind  of  material  --  amorphous  metallic  wires  which  could  be  used  in microwave  components,  and  use  these  wires  to  design  new  kinds  of  attenuators.  Based  on  the fundamental  magnetic  properties  of  amorphous  wires  and  transmission  line  theory,  we  design  a series of experiments focusing on these wires, and analyze all the experimental results.    Experimental  results  show  that  incident  and  reflected  signals  produce  interference  and  generate standing  waves  along  the  wire.  At  given  frequency,  the  insertion  attenuation  S21 [dB]  of  an amorphous wire increases monotonically with dc bias current. The glass cover will influence the  magnetic  domain  structure  in  amorphous  metallic  wires.  Therefore,  it  will  affect  the circumference  permeability  and  change  the  signal  attenuation.  It  is  necessary  to  achieve  the impedance  matching  by  coupling  to  an  inductor  and  a  capacitor  in  the  circuit.  The  impedance matching  makes  the  load  impedance  close  to  the  characteristic  impedance  of  transmission  line. The magnetic wire-based attenuator designed in this thesis work are characterized and compared to conventional pin-diode attenuator.

The continuous and aggressive downscaling of conventional CMOS devices has been driving the vast growth of ICs over the last few decades. As the CMOS downscaling approaches the fundamental limits, novel device architectures such as metallic source/drain Schottky barrier MOSFET (SB-MOSFET) and SB-FinFET are probably needed to further push the ultimate downscaling. The ultimate goal of this thesis is to integrate metallic Ni1-xPtx silicide (x=0~1) source/drain into SB-MOSFET and SB-FinFET, with an emphasis on both material and processing issues related to the integration of Ni1-xPtx silicides towards competitive devices. First, the effects of both carbon (C) and nitrogen (N) on the formation and on the Schottky barrier height (SBH) of NiSi are studied. The presence of both C and N is found to improve the poor thermal stability of NiSi significantly. The present work also explores dopant segregation (DS) using B and As for the NiSi/Si contact system. The effects of C and N implantation into the Si substrate prior to the NiSi formation are examined, and it is found that the presence of C yields positive effects in helping reduce the effective SBH to 0.1-0.2 eV for both conduction polarities. In order to unveil the mechanism of SBH tuning by DS, the variation of specific contact resistivity between silicide and Si substrates by DS is monitored. The formation of a thin interfacial dipole layer at silicide/Si interface is confirmed to be the reason of SBH modification. Second, a systematic experimental study is performed for Ni1-xPtx silicide (x=0~1) films aiming at the integration into SB-MOSFET. A distinct behavior is found for the formation of Ni silicide films. Epitaxially aligned NiSi2-y films readily grow and exhibit extraordinary morphological stability up to 800 oC when the thickness of deposited Ni (tNi) &lt;4 nm. Polycrystalline NiSi films form and tend to agglomerate at lower temperatures for thinner films for tNi≥4 nm. Such a distinct annealing behavior is absent for the formation of Pt silicide films with all thicknesses of deposited Pt. The addition of Pt into Ni supports the above observations. Surface energy is discussed as the cause responsible for the distinct behavior in phase formation and morphological stability. Finally, three different Ni-SALICIDE schemes towards a controllable NiSi-based metallic source/drain process without severe lateral encroachment of NiSi are carried out. All of them are found to be effective in controlling the lateral encroachment. Combined with DS technology, both n- and p-types of NiSi source/drain SB-MOSFETs with excellent performance are fabricated successfully. By using the reproducible sidewall transfer lithography (STL) technology developed at KTH, PtSi source/drain SB-FinFET is also realized in this thesis. With As DS, the characteristics of PtSi source/drain SB-FinFET are transformed from p-type to n-type. This thesis work places Ni1-xPtx (x=0~1) silicides SB-MOSFETs as a competitive candidate for future CMOS technology. / QC20100708 / NEMO, NANOSIL, SINANO