Connections between children's speaking and singing behaviours : implications for education and therapy

The purpose of the study was to investigate potential connections between children's speaking and singing behaviours, as well as to explore the potential use of such connections in speech or voice therapy and in educational settings. The objectives of the study were addressed through an exploratory approach. In the literature review, potential connections between the two vocal behaviours were investigated theoretically from the physiological (including neurological), voice-developmental, psychological and sociological perspectives. Based on the theorising, a model of children's vocal functioning was generated. The model advocates the interconnectedness of all vocal functioning and provides arguments towards the idea of musical elements possessing an enhancing effect on children's vocal functioning. In the empirical phase of the study, the theoretical model was exposed to empirical testing. The pre-pilot study consisted of interviews with eight professional speech and voice therapists. The procedute for the pilot and the main studies consisted of: voice recordings, questionnaires, interviews, observations and a psychological test. The procedure was conducted with four classes of children. Initially, all the participants were treated as one group and, subsequently, each class was looked at separately and treated as a case-study. In total, 76 7-10-year old children participated. In addition, interviews were carried out with the teachers of each class. Both quantitative and qualitative analyses were used. The main findings were that children's speaking and singing behaviouts are connected through physiological, psychological and sociological routes, but not through the developmental route. Particularly strong evidence for the interconnectedness of the vocal behaviouts was found from the voice-scientific, psychological and sociological perspectives. The findings imply that children's speaking and singing behaviours are related and, therefore, it may be possible to enhance the quality and functioning of one vocal behaviour through the other. The findings also imply that children's vocal health is connected to a variety of holistic factors and that singing can potentially be used as a means to target these factors. Such findings have significant implications for both educational and therapeutic practice.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Reconfigurable frequency coding of triggered single photons in the telecom C--band

In this work, we demonstrate reconfigurable frequency manipulation of quantum states of light in the telecom C-band. Triggered single photons are encoded in a superposition state of three channels using sidebands up to 53 GHz created by an off-the-shelf phase modulator. The single photons are emitted by an InAs/GaAs quantum dot grown by metal-organic vapor-phase epitaxy within the transparency window of the backbone fiber optical network. A cross-correlation measurement of the sidebands demonstrates the preservation of the single photon nature; an important prerequisite for future quantum technology applications using the existing telecommunication fiber network.Comment: Samuel Gyger and Katharina D. Zeuner contributed equall

Compound semiconductor materials and processing technologies for photonic devices and photonics integration

The advancement of semiconductor optoelectronics relies extensively on materials and processing technologies of ever-increasing sophistication, such as nanometer-range lithography, epitaxial growth methods with monatomic layer control, and anisotropic etching procedures that allows for the precise sculpturing of device features even in the limit of extreme aspect ratios. However, upcoming application needs puts requirements on optimized designs or device performances, e.g. in terms of integration density, power efficiency, modulation bandwidth or spectral response, which call for innovative and refined methodologies. In the present thesis, we investigate a few different device designs or processing schemes that aims for extended performances or manufacturability as compared to presently available technologies. In specific, we study the design and fabrication of transistor-vertical-cavity surface-emitting lasers (T-VCSELs), the regrowth of InP-based driver electronics in the trenches of arrayed spatial light modulators (SLMs), the epitaxial growth and analysis of quantum dot (QD)-based interband photodetectors, the realization of InGaAs/GaAs QD-based single-photon emitters for the 1.55-μm waveband, as well as the fabrication of discrete and silicon-integrated photonic-crystal surface-emitting lasers (PCSELs).The transistor laser, invented at the University of Illinois around 2006, has received considerable interest due to potential major advantages in modulation bandwidth, noise properties and novel functionality as compared to conventional diode lasers. Here we study the design and fabrication of pnp-type 980-nm AlGaAs/InGaAs/GaAs T-VCSELs. Using an epitaxial regrowth process, an intracavity contacting scheme, and an optimized layer design, continuous-wave (CW) result in terms of threshold, output power and temperature performance comparable to conventional VCSELs could be demonstrated. In addition, the collector-current breakdown mechanism was shown to be due to a band-filling effect rather than an intracavity photon absorption process as previously suggested.A subsequent study regards the epitaxial regrowth for the integration of driver electronics with two-dimensional arrays of spatial light modulators (SLMs). The challenge here relies in controlling the regrowth morphology in the restricted areas that limit the SLM array fill factor. It is shown that the orientation of the SLM array with respect to the crystallographic directions is critical for controlling the regrowth7morphology, with mesa alignments along the &lt;001&gt; directions preferable over the &lt;011&gt; directions. Following this scheme, an optimized etch/regrowth process for top-contacted field-effect transistors is demonstrated.Next, we discuss the development of long-wavelength infrared (LWIR; 8-12 μm) detector elements for thermal imaging. Such detectors have traditionally been realized in the mercury-cadmium-telluride system (MCT; high performance but difficult materials properties resulting in high cost) or using AlGaAs/GaAs quantum-well infrared photodetectors (QWIPs; excellent manufacturing properties but compromised performance figures). In this work we consider interband QD photodetectors based on spatially indirect transitions in the In(Ga)Sb QD/InAs type-II system to combine the respective advantages of MCT detectors and QWIPs. An epitaxial growth process is optimized for photo-response in the LWIR regime, and the QD properties were also studied using excitation power-dependent PL and spatially resolved current-voltage spectroscopy using a scanning-tunneling microscope.Quantum dot-based structures were also studied for the development of single-photon telecommunication-wavelength emitters. In this case, InAs QDs were formed in an In-rich InGaAs metamorphic buffer layer grown on GaAs substrate. This resulted in narrow and bright micro-photoluminescence emission lines from isolated QDs around 1.55 μm at low temperature, thereby making the application of such QDs an interesting alternative approach to InAs/InP QDs for the realization of single-photon emitters for telecommunication-wavelength fiber-based quantum networks.Finally, we describe the development of silicon-integrated and discrete photonic-crystal surface-emitting lasers (PCSELs). In the former case, a transfer-print process is used to combine an SOI-based PC structure with an InP-based active region. This results in an ultra-shallow device structure and a buried tunnel-junction configuration is used for current injection. In the latter case, the metal-organic vapor-phase epitaxy (MOVPE) growth conditions are tuned to form perfectly encapsulated cavities in the InP matrix. Low-threshold lasing is thereby obtained from optical pumping.Framstegen inom halvledarbaserad optoelektronik baseras i stor utsträckning på alltmer förfinad material och processteknologi, såsom litografi i nanometerskala, epitaxiala tillväxtmetoder med atomär skiktkontroll och starkt anisotropisk etsning av avancerade komponentstrukturer. Uppkommande applikationsbehov ställer emellertid allt större krav på optimerad design och komponentprestanda, t.ex. avseende integrationstäthet, energieffektivitet, modulationsbandbredd eller spektral respons, vilket kräver innovativa och förfinade metoder. I denna avhandling undersöks några olika komponentdesigner och tillverkningsmetoder som syftar till utökad prestanda och/eller tillverkningsförmåga jämfört med nu tillgänglig teknologi. Speciellt studeras design och tillverkning av transistor-vertikalkavitetslasrar (T-VCSELs), epitaxiell återodling av InP-baserad drivelektronik i pixelerade ljusmodulatorer (SLM), epitaxiell tillväxt och analys av kvantpricks (QD)-baserade interband-fotodetektorer, realisering av InGaAs/GaAs QD-baserade single-fotonsändare för telekommunikationsområdet, samt tillverkning av diskreta och kiselintegrerade fotonisk-kristall-baserade ytemitterande lasrar ( PCSEL).Transistorlasern, som uppfanns vid University of Illinois omkring 2006, har rönt stort intresse på grund av möjliga prestandafördelar relaterat till moduleringsbandbredd, brusegenskaper och ny funktionalitet jämfört med konventionella diodlasrar. Här studeras design och tillverkning av pnp-typ 980-nm AlGaAs/InGaAs/GaAs T-VCSEL. Med hjälp av en epitaxiell återodlingsprocess, intrakavitetskontakter och optimerad design, demonstreras T-VCSELs med continuous wave (CW)-resultat i termer av tröskel, uteffekt och temperaturprestanda jämförbara med konventionella VCSELs. Dessutom visas genombrottsmekanismen för kollektorström bero på en bandfyllnadseffekt snarare än en foton-assisterad absorptionsprocess som tidigare föreslagits.I ett annat sammanhang studeras epitaxial återodling för integration av drivelektronik i tvådimensionella pixelerade ljusmodulatorer (SLM). Utmaningen här består i att kontrollera återväxtmorfologin i de begränsade områdena som avskiljer SLM-pixlarna. Det visas att komponenternas orientering med avseende på de kristallografiska riktningarna är avgörande för att kontrollera9återodlingens morfologi. Det visas att en orientering av pixel-raderna längs &lt;001&gt;- snarare än &lt;011&gt; -riktningarna har en fördel i det sammanhanget. Baserat på dessa resultat utvecklas en etsnings/ återodlingsprocess för toppkontakterade fälteffekttransistorer.Därefter diskuteras utvecklingen av långvågiga infraröda (LWIR; 8-12 μm) detektorelement för värmekameror. Sådana detektorer har traditionellt realiserats i kvicksilver-kadmium-telluridsystemet (MCT; högpresterande men svåra materialegenskaper som resulterar i höga kostnader) eller med användning av AlGaAs/GaAs kvantbrunnsbaserad infraröda fotodetektorer (QWIPs; utmärkta tillverkningsegenskaper men mer modest prestanda). I detta arbete undersöks interband-QD-fotodetektorer baserade på rumsligt indirekta övergångar i In(Ga)Sb QD/InAs typ II-systemet för att kombinera prestanda och tillverkningsfördelarna i MCT- och QWIP-teknologierna. En epitaxiell tillväxtprocess optimerades för fotorespons i LWIR-området, och QD-egenskaperna studerades dessutom explicit med excitationsberoende PL och rumsligt upplöst tunnelspektroskopi med hjälp av ett sveptunnelmikroskop.Kvantprickbaserade strukturer studerades också för utveckling av singelfotonemittrar i telekommunikationvåglängdsområdet. I detta fall bildades InAs kvantprickar i ett In-rikt InGaAs metamorfiskt buffertlager odlat på ett GaAs-substrat. Detta resulterade i smala och ljusstarka fotoluminiscensinjer från isolerade kvantprickar vid en vågländ runt 1,55 μm vid låg temperatur. Detta gör tillämpningen av sådana kvantprickar till ett intressant alternativt till InAs/InP kvantprickar för realisering av singelfotonemittrar för telekomvåglängdsbaserade kvantnätverk.Slutligen beskrivs utvecklingen av kiselintegrerade samt diskreta fotonisk-kristall-baserade ytemitterande lasrar (PCSELs). I det förra fallet används en transfer-print-process för att kombinera en SOI-baserad fotonisk-kristall-struktur med InP-baserade aktivt material. Detta resulterar i en extremt kompakt komponentstruktur där en begravd tunneldiod används för ströminjektion. I det senare fallet justeras tillväxtparametrarna i MOVPE-processen för skapa en fotonisk-kristall-struktur med luft-fyllda håligheter i InP-materialet. Lasring uppvisades genom optisk pumpning.QC 20201022</p

Compound semiconductor materials and processing technologies for photonic devices and photonics integration

The advancement of semiconductor optoelectronics relies extensively on materials and processing technologies of ever-increasing sophistication, such as nanometer-range lithography, epitaxial growth methods with monatomic layer control, and anisotropic etching procedures that allows for the precise sculpturing of device features even in the limit of extreme aspect ratios. However, upcoming application needs puts requirements on optimized designs or device performances, e.g. in terms of integration density, power efficiency, modulation bandwidth or spectral response, which call for innovative and refined methodologies. In the present thesis, we investigate a few different device designs or processing schemes that aims for extended performances or manufacturability as compared to presently available technologies. In specific, we study the design and fabrication of transistor-vertical-cavity surface-emitting lasers (T-VCSELs), the regrowth of InP-based driver electronics in the trenches of arrayed spatial light modulators (SLMs), the epitaxial growth and analysis of quantum dot (QD)-based interband photodetectors, the realization of InGaAs/GaAs QD-based single-photon emitters for the 1.55-μm waveband, as well as the fabrication of discrete and silicon-integrated photonic-crystal surface-emitting lasers (PCSELs).The transistor laser, invented at the University of Illinois around 2006, has received considerable interest due to potential major advantages in modulation bandwidth, noise properties and novel functionality as compared to conventional diode lasers. Here we study the design and fabrication of pnp-type 980-nm AlGaAs/InGaAs/GaAs T-VCSELs. Using an epitaxial regrowth process, an intracavity contacting scheme, and an optimized layer design, continuous-wave (CW) result in terms of threshold, output power and temperature performance comparable to conventional VCSELs could be demonstrated. In addition, the collector-current breakdown mechanism was shown to be due to a band-filling effect rather than an intracavity photon absorption process as previously suggested.A subsequent study regards the epitaxial regrowth for the integration of driver electronics with two-dimensional arrays of spatial light modulators (SLMs). The challenge here relies in controlling the regrowth morphology in the restricted areas that limit the SLM array fill factor. It is shown that the orientation of the SLM array with respect to the crystallographic directions is critical for controlling the regrowth7morphology, with mesa alignments along the &lt;001&gt; directions preferable over the &lt;011&gt; directions. Following this scheme, an optimized etch/regrowth process for top-contacted field-effect transistors is demonstrated.Next, we discuss the development of long-wavelength infrared (LWIR; 8-12 μm) detector elements for thermal imaging. Such detectors have traditionally been realized in the mercury-cadmium-telluride system (MCT; high performance but difficult materials properties resulting in high cost) or using AlGaAs/GaAs quantum-well infrared photodetectors (QWIPs; excellent manufacturing properties but compromised performance figures). In this work we consider interband QD photodetectors based on spatially indirect transitions in the In(Ga)Sb QD/InAs type-II system to combine the respective advantages of MCT detectors and QWIPs. An epitaxial growth process is optimized for photo-response in the LWIR regime, and the QD properties were also studied using excitation power-dependent PL and spatially resolved current-voltage spectroscopy using a scanning-tunneling microscope.Quantum dot-based structures were also studied for the development of single-photon telecommunication-wavelength emitters. In this case, InAs QDs were formed in an In-rich InGaAs metamorphic buffer layer grown on GaAs substrate. This resulted in narrow and bright micro-photoluminescence emission lines from isolated QDs around 1.55 μm at low temperature, thereby making the application of such QDs an interesting alternative approach to InAs/InP QDs for the realization of single-photon emitters for telecommunication-wavelength fiber-based quantum networks.Finally, we describe the development of silicon-integrated and discrete photonic-crystal surface-emitting lasers (PCSELs). In the former case, a transfer-print process is used to combine an SOI-based PC structure with an InP-based active region. This results in an ultra-shallow device structure and a buried tunnel-junction configuration is used for current injection. In the latter case, the metal-organic vapor-phase epitaxy (MOVPE) growth conditions are tuned to form perfectly encapsulated cavities in the InP matrix. Low-threshold lasing is thereby obtained from optical pumping.Framstegen inom halvledarbaserad optoelektronik baseras i stor utsträckning på alltmer förfinad material och processteknologi, såsom litografi i nanometerskala, epitaxiala tillväxtmetoder med atomär skiktkontroll och starkt anisotropisk etsning av avancerade komponentstrukturer. Uppkommande applikationsbehov ställer emellertid allt större krav på optimerad design och komponentprestanda, t.ex. avseende integrationstäthet, energieffektivitet, modulationsbandbredd eller spektral respons, vilket kräver innovativa och förfinade metoder. I denna avhandling undersöks några olika komponentdesigner och tillverkningsmetoder som syftar till utökad prestanda och/eller tillverkningsförmåga jämfört med nu tillgänglig teknologi. Speciellt studeras design och tillverkning av transistor-vertikalkavitetslasrar (T-VCSELs), epitaxiell återodling av InP-baserad drivelektronik i pixelerade ljusmodulatorer (SLM), epitaxiell tillväxt och analys av kvantpricks (QD)-baserade interband-fotodetektorer, realisering av InGaAs/GaAs QD-baserade single-fotonsändare för telekommunikationsområdet, samt tillverkning av diskreta och kiselintegrerade fotonisk-kristall-baserade ytemitterande lasrar ( PCSEL).Transistorlasern, som uppfanns vid University of Illinois omkring 2006, har rönt stort intresse på grund av möjliga prestandafördelar relaterat till moduleringsbandbredd, brusegenskaper och ny funktionalitet jämfört med konventionella diodlasrar. Här studeras design och tillverkning av pnp-typ 980-nm AlGaAs/InGaAs/GaAs T-VCSEL. Med hjälp av en epitaxiell återodlingsprocess, intrakavitetskontakter och optimerad design, demonstreras T-VCSELs med continuous wave (CW)-resultat i termer av tröskel, uteffekt och temperaturprestanda jämförbara med konventionella VCSELs. Dessutom visas genombrottsmekanismen för kollektorström bero på en bandfyllnadseffekt snarare än en foton-assisterad absorptionsprocess som tidigare föreslagits.I ett annat sammanhang studeras epitaxial återodling för integration av drivelektronik i tvådimensionella pixelerade ljusmodulatorer (SLM). Utmaningen här består i att kontrollera återväxtmorfologin i de begränsade områdena som avskiljer SLM-pixlarna. Det visas att komponenternas orientering med avseende på de kristallografiska riktningarna är avgörande för att kontrollera9återodlingens morfologi. Det visas att en orientering av pixel-raderna längs &lt;001&gt;- snarare än &lt;011&gt; -riktningarna har en fördel i det sammanhanget. Baserat på dessa resultat utvecklas en etsnings/ återodlingsprocess för toppkontakterade fälteffekttransistorer.Därefter diskuteras utvecklingen av långvågiga infraröda (LWIR; 8-12 μm) detektorelement för värmekameror. Sådana detektorer har traditionellt realiserats i kvicksilver-kadmium-telluridsystemet (MCT; högpresterande men svåra materialegenskaper som resulterar i höga kostnader) eller med användning av AlGaAs/GaAs kvantbrunnsbaserad infraröda fotodetektorer (QWIPs; utmärkta tillverkningsegenskaper men mer modest prestanda). I detta arbete undersöks interband-QD-fotodetektorer baserade på rumsligt indirekta övergångar i In(Ga)Sb QD/InAs typ II-systemet för att kombinera prestanda och tillverkningsfördelarna i MCT- och QWIP-teknologierna. En epitaxiell tillväxtprocess optimerades för fotorespons i LWIR-området, och QD-egenskaperna studerades dessutom explicit med excitationsberoende PL och rumsligt upplöst tunnelspektroskopi med hjälp av ett sveptunnelmikroskop.Kvantprickbaserade strukturer studerades också för utveckling av singelfotonemittrar i telekommunikationvåglängdsområdet. I detta fall bildades InAs kvantprickar i ett In-rikt InGaAs metamorfiskt buffertlager odlat på ett GaAs-substrat. Detta resulterade i smala och ljusstarka fotoluminiscensinjer från isolerade kvantprickar vid en vågländ runt 1,55 μm vid låg temperatur. Detta gör tillämpningen av sådana kvantprickar till ett intressant alternativt till InAs/InP kvantprickar för realisering av singelfotonemittrar för telekomvåglängdsbaserade kvantnätverk.Slutligen beskrivs utvecklingen av kiselintegrerade samt diskreta fotonisk-kristall-baserade ytemitterande lasrar (PCSELs). I det förra fallet används en transfer-print-process för att kombinera en SOI-baserad fotonisk-kristall-struktur med InP-baserade aktivt material. Detta resulterar i en extremt kompakt komponentstruktur där en begravd tunneldiod används för ströminjektion. I det senare fallet justeras tillväxtparametrarna i MOVPE-processen för skapa en fotonisk-kristall-struktur med luft-fyllda håligheter i InP-materialet. Lasring uppvisades genom optisk pumpning.QC 20201022</p

Compound semiconductor materials and processing technologies for photonic devices and photonics integration

The advancement of semiconductor optoelectronics relies extensively on materials and processing technologies of ever-increasing sophistication, such as nanometer-range lithography, epitaxial growth methods with monatomic layer control, and anisotropic etching procedures that allows for the precise sculpturing of device features even in the limit of extreme aspect ratios. However, upcoming application needs puts requirements on optimized designs or device performances, e.g. in terms of integration density, power efficiency, modulation bandwidth or spectral response, which call for innovative and refined methodologies. In the present thesis, we investigate a few different device designs or processing schemes that aims for extended performances or manufacturability as compared to presently available technologies. In specific, we study the design and fabrication of transistor-vertical-cavity surface-emitting lasers (T-VCSELs), the regrowth of InP-based driver electronics in the trenches of arrayed spatial light modulators (SLMs), the epitaxial growth and analysis of quantum dot (QD)-based interband photodetectors, the realization of InGaAs/GaAs QD-based single-photon emitters for the 1.55-μm waveband, as well as the fabrication of discrete and silicon-integrated photonic-crystal surface-emitting lasers (PCSELs).The transistor laser, invented at the University of Illinois around 2006, has received considerable interest due to potential major advantages in modulation bandwidth, noise properties and novel functionality as compared to conventional diode lasers. Here we study the design and fabrication of pnp-type 980-nm AlGaAs/InGaAs/GaAs T-VCSELs. Using an epitaxial regrowth process, an intracavity contacting scheme, and an optimized layer design, continuous-wave (CW) result in terms of threshold, output power and temperature performance comparable to conventional VCSELs could be demonstrated. In addition, the collector-current breakdown mechanism was shown to be due to a band-filling effect rather than an intracavity photon absorption process as previously suggested.A subsequent study regards the epitaxial regrowth for the integration of driver electronics with two-dimensional arrays of spatial light modulators (SLMs). The challenge here relies in controlling the regrowth morphology in the restricted areas that limit the SLM array fill factor. It is shown that the orientation of the SLM array with respect to the crystallographic directions is critical for controlling the regrowth7morphology, with mesa alignments along the &lt;001&gt; directions preferable over the &lt;011&gt; directions. Following this scheme, an optimized etch/regrowth process for top-contacted field-effect transistors is demonstrated.Next, we discuss the development of long-wavelength infrared (LWIR; 8-12 μm) detector elements for thermal imaging. Such detectors have traditionally been realized in the mercury-cadmium-telluride system (MCT; high performance but difficult materials properties resulting in high cost) or using AlGaAs/GaAs quantum-well infrared photodetectors (QWIPs; excellent manufacturing properties but compromised performance figures). In this work we consider interband QD photodetectors based on spatially indirect transitions in the In(Ga)Sb QD/InAs type-II system to combine the respective advantages of MCT detectors and QWIPs. An epitaxial growth process is optimized for photo-response in the LWIR regime, and the QD properties were also studied using excitation power-dependent PL and spatially resolved current-voltage spectroscopy using a scanning-tunneling microscope.Quantum dot-based structures were also studied for the development of single-photon telecommunication-wavelength emitters. In this case, InAs QDs were formed in an In-rich InGaAs metamorphic buffer layer grown on GaAs substrate. This resulted in narrow and bright micro-photoluminescence emission lines from isolated QDs around 1.55 μm at low temperature, thereby making the application of such QDs an interesting alternative approach to InAs/InP QDs for the realization of single-photon emitters for telecommunication-wavelength fiber-based quantum networks.Finally, we describe the development of silicon-integrated and discrete photonic-crystal surface-emitting lasers (PCSELs). In the former case, a transfer-print process is used to combine an SOI-based PC structure with an InP-based active region. This results in an ultra-shallow device structure and a buried tunnel-junction configuration is used for current injection. In the latter case, the metal-organic vapor-phase epitaxy (MOVPE) growth conditions are tuned to form perfectly encapsulated cavities in the InP matrix. Low-threshold lasing is thereby obtained from optical pumping.Framstegen inom halvledarbaserad optoelektronik baseras i stor utsträckning på alltmer förfinad material och processteknologi, såsom litografi i nanometerskala, epitaxiala tillväxtmetoder med atomär skiktkontroll och starkt anisotropisk etsning av avancerade komponentstrukturer. Uppkommande applikationsbehov ställer emellertid allt större krav på optimerad design och komponentprestanda, t.ex. avseende integrationstäthet, energieffektivitet, modulationsbandbredd eller spektral respons, vilket kräver innovativa och förfinade metoder. I denna avhandling undersöks några olika komponentdesigner och tillverkningsmetoder som syftar till utökad prestanda och/eller tillverkningsförmåga jämfört med nu tillgänglig teknologi. Speciellt studeras design och tillverkning av transistor-vertikalkavitetslasrar (T-VCSELs), epitaxiell återodling av InP-baserad drivelektronik i pixelerade ljusmodulatorer (SLM), epitaxiell tillväxt och analys av kvantpricks (QD)-baserade interband-fotodetektorer, realisering av InGaAs/GaAs QD-baserade single-fotonsändare för telekommunikationsområdet, samt tillverkning av diskreta och kiselintegrerade fotonisk-kristall-baserade ytemitterande lasrar ( PCSEL).Transistorlasern, som uppfanns vid University of Illinois omkring 2006, har rönt stort intresse på grund av möjliga prestandafördelar relaterat till moduleringsbandbredd, brusegenskaper och ny funktionalitet jämfört med konventionella diodlasrar. Här studeras design och tillverkning av pnp-typ 980-nm AlGaAs/InGaAs/GaAs T-VCSEL. Med hjälp av en epitaxiell återodlingsprocess, intrakavitetskontakter och optimerad design, demonstreras T-VCSELs med continuous wave (CW)-resultat i termer av tröskel, uteffekt och temperaturprestanda jämförbara med konventionella VCSELs. Dessutom visas genombrottsmekanismen för kollektorström bero på en bandfyllnadseffekt snarare än en foton-assisterad absorptionsprocess som tidigare föreslagits.I ett annat sammanhang studeras epitaxial återodling för integration av drivelektronik i tvådimensionella pixelerade ljusmodulatorer (SLM). Utmaningen här består i att kontrollera återväxtmorfologin i de begränsade områdena som avskiljer SLM-pixlarna. Det visas att komponenternas orientering med avseende på de kristallografiska riktningarna är avgörande för att kontrollera9återodlingens morfologi. Det visas att en orientering av pixel-raderna längs &lt;001&gt;- snarare än &lt;011&gt; -riktningarna har en fördel i det sammanhanget. Baserat på dessa resultat utvecklas en etsnings/ återodlingsprocess för toppkontakterade fälteffekttransistorer.Därefter diskuteras utvecklingen av långvågiga infraröda (LWIR; 8-12 μm) detektorelement för värmekameror. Sådana detektorer har traditionellt realiserats i kvicksilver-kadmium-telluridsystemet (MCT; högpresterande men svåra materialegenskaper som resulterar i höga kostnader) eller med användning av AlGaAs/GaAs kvantbrunnsbaserad infraröda fotodetektorer (QWIPs; utmärkta tillverkningsegenskaper men mer modest prestanda). I detta arbete undersöks interband-QD-fotodetektorer baserade på rumsligt indirekta övergångar i In(Ga)Sb QD/InAs typ II-systemet för att kombinera prestanda och tillverkningsfördelarna i MCT- och QWIP-teknologierna. En epitaxiell tillväxtprocess optimerades för fotorespons i LWIR-området, och QD-egenskaperna studerades dessutom explicit med excitationsberoende PL och rumsligt upplöst tunnelspektroskopi med hjälp av ett sveptunnelmikroskop.Kvantprickbaserade strukturer studerades också för utveckling av singelfotonemittrar i telekommunikationvåglängdsområdet. I detta fall bildades InAs kvantprickar i ett In-rikt InGaAs metamorfiskt buffertlager odlat på ett GaAs-substrat. Detta resulterade i smala och ljusstarka fotoluminiscensinjer från isolerade kvantprickar vid en vågländ runt 1,55 μm vid låg temperatur. Detta gör tillämpningen av sådana kvantprickar till ett intressant alternativt till InAs/InP kvantprickar för realisering av singelfotonemittrar för telekomvåglängdsbaserade kvantnätverk.Slutligen beskrivs utvecklingen av kiselintegrerade samt diskreta fotonisk-kristall-baserade ytemitterande lasrar (PCSELs). I det förra fallet används en transfer-print-process för att kombinera en SOI-baserad fotonisk-kristall-struktur med InP-baserade aktivt material. Detta resulterar i en extremt kompakt komponentstruktur där en begravd tunneldiod används för ströminjektion. I det senare fallet justeras tillväxtparametrarna i MOVPE-processen för skapa en fotonisk-kristall-struktur med luft-fyllda håligheter i InP-materialet. Lasring uppvisades genom optisk pumpning.QC 20201022</p

Cross-Sectional Scanning Tunneling Microscopy Studies of In 1-xGax Sb/InAs Quantum Dots

This thesis focuses on the characterization of In 0,4 Ga 0,6 Sb/InAs and InSb/InAs quantum dots using Cross-Sectional Scanning Tunneling Microscopy (X-STM). Quantum dots (QDs) are small and spatially confined semiconductor nanostructures with a size-dependent band gap. This property makes them very attractive for devices such as sensors, solar cells and lasers. The QDs analyzed in this thesis were grown using Metal-Organic Vapor Phase Epitaxy (MOVPE) and are meant to be utilized in long wavelength infrared (LWIR) (~8μm) detectors. To study buried QDs by X-STM, the sample has to be cleaved and measured in Ultra High Vacuum (UHV). In order to do this, a cleaving apparatus was built and installed on an STM system. A sample preparation methodology was worked out in order to make the samples ready for cleaving. An easy method for finding the QDs with the X-STM was also developed. Measurements resulted in a number of atomically resolved images, revealing the QD layer morphology. Furthermore, larger images were captured in order to study growth defects. Because of the high dot density, at low resolution the QDs were perceived as quantum wells. It was only at atomic resolution that QDs could be resolved. The observed dot sizes ranged between ~3 nm (InSb) and ~8 nm (In 0,4 Ga 0,6 Sb) in diameter

Faculty of Computing lecturer workload accounting system

“Datorikas fakultātes docētāju slodžu uzskaites sistēma” ir tīmeklī bāzēta sistēma, kuras izstrādes nolūks ir vienkāršot un sistematizēt darba slodzes uzskaiti un algu aprēķināšanu Latvijas Universitātes docētajiem un lietvežiem. Sistēma sniedz lietvežiem iespēju ātri un ērti pārbaudīt un akceptēt docētāju akadēmiska gada darba slodzi, pievienot un apskatīt kursus, docētājus un to informāciju. Docētāji var veidot LU akadēmiska personāla slodzes karti, pēc kuras tiem tiek rēķinātā alga, apskatīt pasniegtos kursus, amatus, nepieciešamības gadījumā, sazināties ar lietvežiem, u.c. iespējas. Sistēma tika paredzētā vairākām LU fakultātēm.“Faculty of Computing lecturer workload accounting system” is a Web-based system, whose development purpose is to simplify and systematize accounting of a workload and salary calculation for Latvian University lecturers and secretaries. System gives secretaries the opportunity of fast and comfortable verification of lecturer academic year workload, manage courses, lecturers and their information. Using the system, lecturers can create LU academic staff workload map, according to which their salary is calculated, manage their taught courses, taken posts, communicate with secretaries in case of necessity, etc. System intended to work with many faculties

Strain-controlled quantum dot fine structure for entangled photon generation at 1550 nm

Entangled photon generation at 1550 nm in the telecom C-band is of critical importance as it enables the realization of quantum communication protocols over long distance using deployed telecommunication infrastructure. InAs epitaxial quantum dots have recently enabled on-demand generation of entangled photons in this wavelength range. However, time-dependent state evolution, caused by the fine-structure splitting, currently limits the fidelity to a specific entangled state. Here, we show fine-structure suppression for InAs quantum dots using micromachined piezoelectric actuators and demonstrate generation of highly entangled photons at 1550 nm. At the lowest fine-structure setting, we obtain a maximum fidelity of 90.0 ± 2.7% (concurrence of 87.5 ± 3.1%). The concurrence remains high also for moderate (weak) temporal filtering, with values close to 80% (50%), corresponding to 30% (80%) of collected photons, respectively. The presented fine-structure control opens the way for exploiting entangled photons from quantum dots in fiber-based quantum communication protocols