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Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching., QC 20231013

Buried heterostructure quantum cascade lasers (BH-QCLs) operating at high temperature in mid-infrared (MIR) to THz spectral range are desired for chemical sensing and free-space optical communication (FOC). In this work, Fe doped semi-insulating InP (SI-InP) regrowth is demonstrated in a hydride vapor phase epitaxy (HVPE) reactor for advanced MIR and THz BH-QCLs grown by MBE and MOCVD. SI-InP regrowth is implemented in THz QCL pillar arrays and narrow width and reverse-taper MIR BH-QCLs for efficient heat dissipation. By exploiting SI-InP regrowth, the parasitic capacitance in MIR distributed feedback BH-QCL can be suppressed, which is exploited for high speed FOC application., Part of ISBN 9781510659858QC 20231030

GaAsP/Si with high crystalline quality fabricated by cost-effective heteroepitaxial technology is a promising pathway for realizing low-cost Si-based tandem solar cell with efficiency higher than 30%. Herein, hydride vapor-phase epitaxy is used to perform selective area growth of GaAsP with high lateral coverage, referred to as epitaxial lateral overgrowth (ELOG). The ELOG is performed on GaAs-based substrates as a prestudy, followed by GaAs/Si and GaAsP/Si seed wafers employing chemical mechanical polishing to fabricate full 2 00 GaAsP/Si templates. These are subsequently used to grow and process GaAsP/Si pn-junction structures for electrical characterization. The ELOG GaAsP is studied by spatially resolved photoluminescence (PL) mapping and high-resolution X-ray diffraction measurements. PL analysis of the GaAsP/GaAs ELOG samples reveals an enhanced P-incorporation during lateral growth of GaAsP. This is also observed for the GaAsP/Si ELOG templates along with evidence of improved material quality, clearly distinguishing the laterally grown GaAsP from the planar growth directly above the Si substrate. Leakage pathways causing reduced electrical performance of the ELOG GaAsP/Si pn-junction structures are identified., QC 20230607

Orientation-patterned gallium phosphide (OP-GaP) has been grown heteroepitaxially on OP gallium arsenide (GaAs) templates using hydride vapor phase epitaxy (HVPE). The effect of OP-GaAs template fabrication methods of epitaxial-inversion and wafer bonding on the heteroepitaxial OP-GaP growth has been investigated. OP-GaP layers with a growth rate of up to 35 mu m/h and excellent domain fidelity were obtained. The growth rate and the domain fidelity have been revealed/studied by scanning electron microscope (SEM). In addition, we demonstrate that the crystalline quality of the individual domains, namely, the substrate-oriented domains (ODs) and the inverted domains (IDs), can be investigated by high-resolution x-ray diffraction reciprocal space mapping (HRXRDRSM), which can also indicate the domain fidelity. Attempts to increase the growth rate and improve the domain fidelity by increasing the III and V group precursors resulted in either an increase in the growth rate in the OP-GaP layers grown on epitaxial inversion OP-GaAs template at the expense of the domain crystalline quality and fidelity or an improvement in the crystalline quality of the domains at the expense of the growth rate in the OP-GaP layers grown on wafer-bonded OP-GaAs templates. In the case of OP-GaP grown on OP-GaAs templates prepared by epitaxial inversion, the crystalline quality of the ODs is better than that of the IDs, but it shows that the quality of the inverted layer in the template influences the quality and fidelity of the grown domains. To the authors' knowledge, exploitation of HRXRDRSM studies on OP-GaP to establish the crystalline quality of its individual domains (ODs and IDs) is the first of its kind. OP-ZnSe grown on OP-GaAs templates has also been included in this study to further emphasize the potential of this method. We propose from this study that once the growth rate is optimized from SEM studies, HRXRDRSM analysis alone can be used to assess the structural quality and to i, QC 20230316

This work covers the implementation of highly specialized epitaxial techniques enabled by the near-equilibrium hydride vapor-phase epitaxy growth process in III-V/Si integration for Si-based tandem solar cells and photoelectrochemical reactions, quasi phase matching GaP structures on GaAs substrates, and regrowth of InP:Fe on quantum cascade lasing structures. III-V/Si integration is an important topic in several fields of research with a significant one being solar energy harvesting. Combining the economic benefits of Si with the advantageous and flexible optical and electronic properties of III-V’s represents significant improvements in both photovoltaic and photoelectrochemical applications. GaAsP is a promising candidate for Si-based tandem solar cells, but it has seen much less research compared to other III-V compounds. Establishing a cost-efficient method for integrating GaAsP on Si could pave the way for significant improvements in photovoltaics. However, there are many technological challenges with this integration, some of which are addressed in this work using advanced epitaxial techniques. A fabrication process for full 2” wafer GaAsP/Si templates is developed. This is based on the epitaxial lateral overgrowth technique to reduce misfit dislocations, which utilizes the inherent selectivity and high growth rate of hydride vapor phase epitaxy. Extensive work is also done to establish control of the crystalline quality and composition of planar and laterally grown GaAsP on both GaAs and Si. Planar GaAsP/Si solar cell structures are grown based on the optimization work, and a process for fabricating devices out of these is developed. Work on III-V/Si integration is also done towards photoelectrochemical applications; p-GaP is grown on Si by direct heteroepitaxy, which requires a specialized technique called vapor mixing epitaxy. This utilizes a specialized precursor injection scheme in order to allow the growth to take place at a much lower temperature than, Den här avhandlingen beskriver avancerade epitaxiella tekniker med hydridbaserad ångfasepitaxi: en tillväxtprocess som tar plats nära kemisk jämvikt. Teknikerna användes för integrering av III-V/Si – integrering för kiselbaserade tandemsolceller och fotoelektrokemiska reaktioner, odling av kvasifasmatchade GaP-strukturer på GaAs och återodling av InP:Fe på kvantkaskadlasrande strukturer. Integrering av III-V – material på kisel är ett viktigt ämne inom flera fält, däribland utnyttjande av solenergi. Kombinationen av de ekonomiska fördelarna hos kisel med de fördelaktiga och flexibla optoelektroniska egenskaperna hos III-V – material representerar avsevärda framsteg för applikationer inom både solcellsteknik och fotoelektrokemi. GaAsP är en bra kandidat för kiselbaserade tandemsolceller, men har inte undersökts lika utförligt som andra III-V material. Genom att etablera en kostnadseffektiv integrationsteknik för GaAsP på kisel skulle viktiga framsteg inom solcellsteknik möjliggöras. Däremot finns det många stora teknologiska utmaningar för sådan integration, några av vilka adresseras i det här arbetet genom implementering av specialiserade epitaxiella tekniker. En tillverkningsprocess för 2” – skivor av GaAsP/Si har utvecklats. Den baseras på lateral epitaxiell täckning för att filtrera bort gittermissmatchdislokationer, vilket utnyttjar den karaktäristiska selektiviteten och höga tillväxthastigheten hos hydridbaserad ångfasepitaxi. Metoder för att kontrollera sammansättningen och kristallkvalitén hos både vertikalt och lateralt odlad GaAsP/Si och GaAsP/GaAs har också undersökts utförligt. Solcellsstrukturer har odlats baserat på undersökningen och ett processflöde för att tillverka solceller has designats och etablerats. III-V/Si integration har också undersökts för fotoelektrokemiska applikationer där p-GaP har odlats direkt på kisel. Detta kräver en specialiserad teknik, kallad för ångblandningsepitaxi, där gasinjiceringen är specialanpassad för att låta odlingen

Heteroepitaxial Zn-doped p-GaP was grown on (001) GaAs, (001) Si and (111) Si substrates by hydride vapor phase epitaxy for solar-driven photoelectrochemical applications of hydrogen generation by water splitting and CO2 reduction. Growth of GaP on Si was realized through the implementation of a low-temperature buffer layer, and the morphology and crystalline quality were enhanced by optimizing the precursor flows and pre-heating ambient substrate. The p-GaP/GaAs and p-GaP/Si samples were processed to photoelectrodes with an amorphous TiO2 coating for CO2 reduction and a combination of TiO2 layer and mesoporous tungsten phosphide catalyst for water splitting. P-GaP/GaAs with suitable Zn-doping concentration exhibited photoelectrochemical performance comparable to homoepitaxial p-GaP/GaP for water splitting and CO2 reduction. Degradation of photocurrent in p-GaP/Si photoelectrodes is observed in PEC water splitting due to the high density of defects arising from heteroepitaxial growth., QC 20230124

We present a reverse-taper quantum cascade laser (QCL) emitting at 4.6 mu m, a novel-geometry device that can scale the output power while maintaining good beam quality. Buried-ridge waveguides with tapered and straight regions were formed by ICP etching and HVPE regrowth - the tapered region scales the output power, while the emitting facet is located at the narrow-end taper section, which provides mode filtering by suppressing high-order spatial modes. Beam profiles were observed under quasi-continuous-wave (QCW)/CW operation and beam quality (M-2) measurements along with beam-stability measurements were performed - a small degree of collimated-beam centroid movement (<0.46 mrad, peak-to-peak) was observed, along with M-2 values close to 1 up to similar to 1 W QCW power. Devices of shorter cavity lengths were also investigated, indicating that the output power scales with the core-region volume but results in a small increase in angular deviation., QC 20220506

High crystal quality GaAsP/Si fabricated by cost effective heteroepitaxial technology is promising to realize low-cost Si based tandem solar cell with efficiency higher than 30%. In this work, epitaxial lateral overgrowth (ELOG) of GaAsP/GaAs and GaAsP/GaAs/Si by hydride vapor phase epitaxy (HVPE) and their properties are studied by photoluminescence (PL) mapping. High crystal quality ELOG GaAsP/Si is obtained with enhanced PL intensity and narrow line width indicating reduced defect density provided by ELOG approach., QC 20230622

The transport industry is experiencing a disruption as fully autonomous vehicles are introduced in traffic. The intelligent, driverless vehicles will reduce cost, liberate human effort and increase safety. Today, the hardware technology seems to have reached the required processing power, but the decision-making algorithm still has a long way to go until they’re proven to be road-safe. Among these is the problem of lateral path tracking control. This thesis will consider the lateral control problem with the goal to send the right signal to the steering actuators so that the vehicle follows a predetermined trajectory. The vehicle in question is a triaxial, rigid, electric truck with active steering on both front and rearmost wheels. With servo latency and large inertial parameters in mind, a highly accurate model of the lateral and yaw behavior must be identified in order to predict the vehicle dynamics for a given steering input. Then, the properties of an optimal lateral controller are iteratively improved until a sufficiently low tracking error is obtained. Lastly, the controller is tuned to guarantee robustness for a range of uncertain vehicle parameters. The derived triaxial model with servo actuation is proven to be better at predicting the vehicle dynamics compared to other models common in literature with only one active steering input. When constructing a lateral controller, the importance was shown of considering 1) state feedback control of the lateral error, 2) feedforward control operating on future road curvature, 3) integrating control which combats biases and model errors, 4) using a tailored triaxial model and 5) minimizing the control signal change. Lastly, the derived controller was shown to have a decent stability margin with respect to estimated uncertainties., Transportbranschen är i ett skifte då helt autonoma fordon införs i trafiken. De intelligenta, förarlösa fordonen minskar kostnader, ökar säkerheten och låter oss människor syssla med annat. Idag verkar det som att hårdvarutekniken har den processorkraft som behövs men de beslutsfattande algoritmerna har fortfarande en lång väg att gå tills de har visat sig vara helt vägsäkra. Bland dessa är problemet med lateral styrningskontroll som kommer ses över i denna avhandling. Fordonet i fråga är en rigid lastbil med tre hjulaxlar och aktiv styrning på både de främre och bakersta hjulen. Med tanke på servofördröjningar och de stora tröghetsparametrarna måste en noggrann modell av dynamiken identifieras för att förutspå responsen för en viss styrvinkel. Därefter utvecklas en optimal lågnivåregulator iterativt tills ett tillräckligt lågt spårningsfel erhållits. Slutligen ställs regulatorn in för att garantera robusthet för ett set av osäkra fordonsparametrar Den härledda triaxialmodellen med servostyrning var bevisbart bättre på att förutspå fordonsdynamiken jämfört med andra modeller som återkommer frekvent i litteraturen. Vid regulatorkonstruktionen påvisades vikten av att överväga 1) återkoppling av laterala felet, 2) förhandsgranskning som tittar på den kommande vägkrökningen, 3) integrering av styrfelet som åtgärdar modellfel, 4) en skräddarsydd fordonsmodell med tre axlar och 5) minimering av ändringen utav kontrollsignalen. Slutligen visades den härledda regulatorn ha en skaplig stabilitetsmarginal gentemot uppskattade osäkerheter av parametrar.

Direct heteroepitaxy and selective area growth (SAG) of GaP and GaAs on Si(100) and Si(111) are implemented by low-pressure hydride vapor phase epitaxy (LP-HVPE), which are facilitated by buffer layers grown at 410–490 °C with reactive gas mixing directly above Si substrates. High-density islands observed on GaP buffer layers on Si result in rough morphology and defect formation in the subsequent GaP layers grown at 715 °C. The impact of growth temperature of GaAs buffer layers on the crystal quality of GaAs/Si is studied. A decreased nucleation temperature significantly improves the morphology and crystalline quality of the overall GaAs growth on Si. It is observed that Si(111) substrates are favorable for both GaP and GaAs growths in comparison with Si(100). In SAGs of GaP/Si and GaAs/Si, the high selectivity innate to HVPE is maintained in the used unconventional growth regime. The spatially resolved photoluminescence mapping reveals the material quality of GaAs/Si is enhanced by defect filtering by SAG. The outcomes of this work will pave the way of III–V/Si integration realized by cost-effective HVPE for photonic device applications., QC 20210323

Measurements of beam stability for mid-infrared (IR)-emitting quantum cascade lasers (QCLs) are important for applications that require the beam to travel through air to remote targets, such as free-space communication links. We report beam-quality measurement results of narrow-ridge, 4.6 mu m-emitting buried-heterostructure (BH) QCLs fabricated using ICP etching and HVPE regrowth. Beam-quality measurements under QCW operation exhibit M-2 < 1.2 up to 1 W for similar to 5 mu m-wide ridges. 5 mu m-wide devices display some small degree of centroid motion with increasing output power (< 0.125 mrad), which corresponds to a targeting error of similar to 1.25 cm over a distance of 100 m., QC 20210217

Novel-geometry, 4.6 mu m-emitting BH QCLs were fabricated, where a tapered region scales the output power and, ahead of the emitting aperture, a narrow section provides mode filtering for suppressing high-order spatial modes. Beam-stability measurements indicate a small degree of collimated-beam centroid motion (< 0.25 mrad)., Part of proceedings: ISBN 978-1-6654-4133-9QC 20220509

En av vår tids största samhällsutmaning är den pågående klimatkrisen. En lösning på krisen är att ställa om till ett mer biobaserat samhälle. Energibehovet ökar globalt och vår påverkan på klimatet måste minska. Ett sätt att minska klimatpåverkan är att använda biobränslen och andra förnybara energislag istället för fossila bränslen. Sverige har kommit en bra bit i sin energiomställning mot förnybara energi – inte minst tack vare god tillgång på biobränslen från våra skogar. Biobränslemarknaden har mer eller mindre tecknat in skogsindustrins restströmmar varför uttag nu också sker direkt i samband med avverkningen i skogen. Den största andelen här utgörs utav grenar och toppar, kallad GROT, som tidigare lämnades vid avverkning. GROT-uttag i föryngringsavverkningar medför måttlig ökning av biomassauttaget men en avsevärd ökning i näringsuttaget, vilket kan påverka tillväxten negativt i nästa skogsgeneration. Det har också visats i fältförsök, framförallt på svagare granmarker även om effekten har varierat mycket mellan de olika försöken. I denna studie undersöktes effekten av GROT-uttag på tillväxten i nästa skogsgeneration i ett fältförsök anlagt på lite svagare granmark med fokus på hur länge tillväxteffekten varar. Studiens hypotes är (i) GROT-uttaget i föryngringsavverkning påverkar tillväxten i nästa skogsgeneration negativt, (ii) Om barren lämnas kvar kommer behandlingseffekten bli mindre och kortvarigare. (iii) Tillväxteffekten av GROT-uttaget är tillfällig och inte permanent. Materialet till studien kommer från ett försök i Västerbotten. Försöket är ett randomiserat blockförsök med fyra upprepningar och har tre försöksled (1) kontrollen (K) där enbart stamveden skördats; (2) helträdsuttag (HTU) där hela biomassan ovan stubben skördats; (3) helträdsuttag där all biomassa ovan stubben utom barren skördats (HTUB). Den data som användes från försöket var korsklavad diameter från alla träd och höjd från provträd som slumpades ut för att få fram volymen för bestånd, One of the greatest societal challenges of today is the ongoing climate crisis. A solution to this problem is the conversion of our society to a bio based one. As the need for energy is rising globally, our impact on the climate have to be reduced. One way towards achieving this is to change from fossil-based fuels to renewable ones. Sweden has come far in this aspect, in large thanks to the easy access to biofuel from the forest. The biofuel market is committed to the residual material from the forest industry, which is why today extraction of biofuel is done in connection with fellings within the forest. The greatest share of the extraction is made up out of branches and tops, so called slash, which previously had been left behind when the area where clear-felled. Slash harvest in final felling amounts to a moderate increase in biomass extraction but a considerable increase in nutrition extraction, which could affect the growth of the coming forest generation. The negative effect has been shown in field tests, especially on leaner spruce land, even though the effects have varied much in between the tests. This study focuses on studying the effect of slash harvest on the oncoming forest generation in a field test on leaner spruce land with focus on how long the effects last. The hypothesis of the study is (i) that slash harvest in final felling do affect the growth in the next forest generation negatively. (ii) if the needles are left behind the negative effect will be smaller and shorter. (iii) the effect of slash harvest is temporary and not permanent. The studies materials come from a field experiment in Västerbotten in northern Sweden. The experiment was established with a randomized block design with four replicates and three treatments (1) control (K) where only stem wood was harvested; (2) whole tree harvest ( HTU) where all biomass above the stump was harvested; (3) whole tree harvest where all the biomass above the stump where harvested except the needles

Heteroepitaxial growth of orientation‐patterned (OP) GaP (OP‐GaP) on wafer‐bonded OP‐GaAs templates is investigated by low‐pressure hydride vapor phase epitaxy for exploiting the beneficial low two‐photon absorption properties of GaP with the matured processing technologies and higher‐quality substrates afforded by GaAs. First, GaP homoepitaxial selective area growth (SAG) is conducted to investigate the dependence of GaP SAG on precursor flows and temperatures toward achieving a high vertical growth rate and equal lateral growth rate in the [110] and [-110]‐oriented openings. Deteriorated domain fidelity is observed in the heteroepitaxial growth of OP‐GaP on OP‐GaAs due to the enhanced growth rate on domain boundaries by threading dislocations generated by 3.6% lattice matching in GaP/GaAs. The dependence of dislocation dynamics on heteroepitaxial growth conditions of OP‐GaP on OP‐GaAs is studied. High OP‐GaP domain fidelity associated with low threading dislocation density and a growth rate of 57 μm h−1 are obtained by increasing GaCl flow. The properties of heteroepitaxial GaP on semi‐insulating GaAs is studied by terahertz time‐domain spectroscopy in the terahertz range. The outcomes of this work will pave the way to exploit heteroepitaxial OP‐GaP growth on OP‐GaAs for frequency conversion by quasi‐phase‐matching in the mid‐infrared and terahertz regions., QC 20191111

Quasi-phase-matched orientation-patterned GaP (OP-GaP) is an attractive technology for achieving mid-IR and terahertz (THz) radiation enabled by nonlinear frequency conversion, because of its low two-photon absorption (2PA) down to 1 µm. High crystalline quality of OP-GaP template and subsequent thick layer growth is required to exploit the benefit of low 2PA of GaP pumped with short wavelength lasers [1]. In this work, we present the development of heteroepitaxial growth of OP-GaP on wafer fused OP-GaAs template with high growth rate and good domain fidelity. The conductivity of the GaP grown on planar GaAs was investigated in the THz region., SyskonpostNot duplicate with DiVA 1429993QC 20200623

Djupa neurala nätverk (DNN) används i ett brett spektrum av uppgifter som röstigenkänning, bildklassificering och spamidentifiering. Det har emellertid visat sig att nätverken kan felklassifiera indata när en liten, noga utvald störning läggs till den. Många adversariella maskininlärningsattacker har föreslagits för att skapa sådana störningar, ofta med målet att hitta den minsta möjliga störningen. I denna studie är DNN tränade för att klassificera bilder. Två adversariella metoder (IFGM och DeepFool) analyseras sedan och jämförs när det gäller att hitta den minsta störningen för att orsaka felklassificering, med minsta beräkningsmässiga ansträngning. De två iterativa, gradientbaserade metoderna implementeras i fyra avståndsmått: L0, L1, L2, Linfinity. Det överraskande resultatet är att även om DeepFool använder en mer sofistikerad optimeringsstrategi, är den inte bättre än IFGM. Vidare finner IFGM en mindre störning under samma givna tidsspann. Även i den riktade regimen är IFGM bättre än DeepFool. Slutligen föreslås en snabb L0-attack som strävar efter att ändra så få pixlar som möjligt för att orsaka felklassificering., Deep neural networks (DNN) are used in a wide range of tasks such as voice recognition, image classification and spam-mail detection. However, it has been shown that the networks can misclassify an input when a small, carefully chosen perturbation is added to it. Many adversarial machine learning attacks have been proposed to create such samples, often with the goal of finding the smallest possible perturbation. In this study, three DNN image classification algorithms are constructed. Two adversarial methods (IFGM and DeepFool) are then analyzed and compared in terms of finding the smallest perturbation to cause misclassification of the networks, with the least computational effort. The two iterative, gradient-based methods are implemented in four distance metrics: L0, L1, L2 and Linfinity. The surprising result is that even though DeepFool uses a more sophisticated optimization strategy it does not perform significantly better than IFGM. Furthermore, IFGM actually finds a smaller perturbation with the same amount of time given. Also, in the targeted regime, IFGM performs better than DeepFool. Lastly, a fast L0-attack is suggested that strives to perturb as few pixels as possible to cause misclassification.

Heteroepitaxial growth of orientation-patterned GaP on patterned GaAs template was developed by using hydride vapor phase epitaxy for quasi-phase-matching applications. We present the growth with well-defined periodic boundaries between (001) and (00 1) GaP domains. The GaP layer on planar GaAs was characterized by terahertz time-domain spectroscopy and the conductivity of GaP (0.16 S cm-1) was obtained in terahertz range., Not duplicate with DiVA 1366349Part of proceedings: ISBN 978-1-7281-0080-7QC 20230921

In this work, we investigated the Si pre-amorphization implantation (PAI) assisted low temperatureannealing process to activate boron implantation in n-Si in a hydride vapor phase epitaxy (HVPE) reactor, which canbe used for the Si subcell fabrication in the III-V/Si tandem solar cells enabled by the corrugated epitaxial lateralovergrowth (CELOG). A uniform boron activation in Si and a low emitter sheet resistance of 77 /sq was obtained atannealing temperatures of 600-700°C. High-resolution x-ray diffraction was used to study the recrystallization ofamorphous silicon and the incorporation of boron dopants in Si. Hall measurements revealed p-type carrierconcentrations in the order of 1020 cm-3. The n-Si wafers with B implantation activated at 700°C by HVPE wereprocessed to solar cells and characterized by the standard light-current-voltage measurement under AM1.5 spectrumand external quantum efficiency measurements. The developed B implantation and low temperature activationprocesses are applied to the InP/Si seed template preparation for CELOG, on which CELOG GaInP over a Si subcellwith a direct heterojunction was demonstrated.

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QC 20220930