Fabrication and characterisation of RGB LEDs based on nanowire technology

The white light LEDs of today are usually based on a blue LED and a phosphor, converting the blue light to longer wavelengths. While these phosphor-converted LEDs are extremely efficient compared to incandescent light or fluorescent light, there is still plenty of room for improvement. In the conversion between blue light and light of lower energy approximately 25-45 % of the radiant power is lost as heat [1]. A more efficient solution is to use white light sources based on RGB LEDs. Since these LEDs do not require phosphor conversion the efficiency has potential to be much higher compared to today’s white light sources. High efficiency blue LEDs are based on an InGaN quantum well and barrier layers of GaN. By altering the In content in InGaN the bandgap can be tuned for emission from UV to red light, which makes the material system a good candidate to be used in fabrication of RGB LEDs. In green and red LEDs the In content in the quantum well is higher compared to blue LEDs which gives rise to more strain between the quantum well and GaN barrier layers. The strain induces piezoelectric charges which spatially separates electrons and holes in the quantum well leading to lower radiative recombination efficiency (quantum-confined Stark effect). The use of InGaN barrier layers would thus enable fabrication of red and green LEDs of higher efficiency, but the main problem is that it is very hard to synthesise thick layers of InGaN with high material quality. The poor crystal quality is partly due to strain induced dislocations and partly due to phase separation and In content fluctuations [2], which will reduce the efficiency of the device [3]. However it has been shown that thick InGaN layers of high material quality can be synthesised in MOCVD grown nanocrystals of InGaN. These nanocrystals, or platelets (truncated pyramids with a flat c-plane), can be used as dislocation free substrates for growth of LEDs, which enables the use of InGaN barrier layers instead of GaN. The strain between the quantum well and barriers in In rich quantum wells is thus reduced which makes it possible to fabricate red and green LEDs of high efficiency. The reduced strain between the barriers and the quantum well leads to a decrease of the quantum-confined Stark effect and therefore potential of higher efficiency LEDs. In this thesis the potential of nano RGB LEDs based on InGaN and GaN platelets is evaluated and the results are promising. During the project an LED device design for LEDs based on (In)GaN platelets was developed, characterised (electrically and electroluminescence) and optimised (spacer layer thicknesses, contact materials). The implemented device design works well. Parasitic currents outside the active area are negligible and the devices show much improved stability compared to previous designs. The device design is based on parallel connected platelets in the device area and lifted bond pads outside of the device area. The bond pads are lifted by a thick spacer layer (resist) in order to enable easy bonding and avoid shunt current. A range of devices of different size were studied, from single platelets (<1μm) to tens of thousands of platelets (400μmx400μm) and the crystal homogeneity is shown to be very important for the device performance. The current rectification is excellent for single platelet devices but decreases with increased number of platelets in the device. While work lies ahead in improving homogeneity, efficiency and device design, this technology is unique in achieving high quality material with very high In content and an extremely small light emission area. Not only are these structures interesting for high-efficiency RGB illumination, but also for microLED displays - potentially with pixel size an order of magnitude smaller than what is possible today

Low-Temperature Characteristics of Nanowire Network Demultiplexer for Qubit Biasing

In current quantum computers, most qubit control electronics are connected to the qubit chip inside the cryostat by cables at room temperature. This poses a challenge when scaling the quantum chip to an increasing number of qubits. We present a lateral nanowire network 1-to-4 demultiplexer design fabricated by selective area grown InGaAs on InP, suitable for on chip routing of DC current for qubit biasing. We have characterized the device at cryogenic temperatures, and at 40 mK the device exhibits a minimum inverse subthreshold slope of 2 mV/dec, which is encouraging for low power operation. At low drain bias, the transmission breaks up into several resonance peaks due to a rough conduction band edge; this is qualitatively explained by a simple model based on a 1D real space tight-binding nonequilibrium Green's functions model

Proteomics and multivariate modelling reveal sex-specific alterations in distinct regions of human carotid atheroma

BackgroundAtherosclerotic lesions are comprised of distinct regions with different proteomic profiles. Men and women develop differences in lesion phenotype, with lesions from women generally being more stable and less prone to rupture. We aimed to investigate the differences in proteomic profiles between sexes, including distinct lesion regions, to identify altered proteins that contribute to these differences observed clinically.MethodsCarotid endarterectomy samples (ten men/ten women) were obtained, and intraplaque biopsies from three distinct regions (internal control, fatty streak and plaque) were analysed by tandem-mass spectrometry. Multivariate statistical modelling, using orthogonal partial least square-discriminant analysis, was used to discriminate the proteomes between men and women.ResultsMultivariate discriminant modelling revealed proteins from 16 functional groups that displayed sex-specific associations. Additional statistics revealed ten proteins that display region-specific alterations when comparing sexes, including proteins related to inflammatory response, response to reactive oxygen species, complement activation, transport and blood coagulation. Transport protein afamin and blood coagulation proteins antithrombin-III and coagulation factor XII were significantly increased in plaque region from women. Inflammatory response proteins lysozyme C and phospholipase A2 membrane-associated were significantly increased in plaque region from men. Limitations with this study are the small sample size, limited patient information and lack of complementary histology to control for cell type differences between sexes.ConclusionsThis pilot study, for the first time, utilises a multivariate proteomic approach to investigate sexual dimorphism in human atherosclerotic tissue, and provides an essential proteomic platform for further investigations to help understand sexual dimorphism and plaque vulnerability in atherosclerosis.Funding Agencies|Swedish Heart Lung Foundation; Torsten and Ragnar Soderbergs Foundation; Stroke Foundation; Olle Engkvist Foundation; Swedish Gamla Tjanarinnor Foundation; Linkoping University Hospital Research Fund</p

Clear differences in cerebrospinal fluid proteome between women with chronic widespread pain and healthy women - a multivariate explorative cross-sectional study

Introduction: Frequent chronic local pain can develop into chronic widespread pain (CWP). The spread of pain is correlated with pain intensity, anxiety, and depression, conditions that ultimately lead to a poor quality of life. Knowledge is incomplete about CWPs etiology, although it has been suggested that both central hyperexcitability and/or a combination with peripheral factors may be involved. Cerebrospinal fluid (CSF) could act as a mirror for the central nervous system as proteins are signal substances that activate the formation of algesics and control nociceptive processes. To this end, this study investigates the CSF protein expression in women with CWP and in female healthy controls. Materials and methods: This study included 12 female patients with CWP diagnosed according to the American College of Rheumatology criteria with 13 healthy age-and sex-matched pain-free subjects. All subjects went through a clinical examination and answered a health questionnaire that registered sociodemographic and anthropometric data, pain characteristics, psychological status, and quality of life rating. CSF was collected by lumbar puncture from each subject. Two-dimensional gel electrophoresis in combination with mass spectrometry was used to analyze the CSF proteome. This study identifies proteins that significantly discriminate between the two groups using multivariate data analysis (MVDA) (i.e., orthogonal partial least squares discriminant analysis [OPLS-DA]). Results: There were no clinically significant levels of psychological distress and catastrophization presented in subjects with CWP. MVDA revealed a highly significant OPLS-DA model where 48 proteins from CSF explained 91% (R-2) of the variation and with a prediction of 90% (Q(2)). The highest discriminating proteins were metabolic, transport, stress, and inflammatory. Conclusion: The highest discriminating proteins (11 proteins), according to the literature, are involved in apoptotic regulations, anti-inflammatory and anti-oxidative processes, the immune system, and endogenous repair. The results of this explorative study may indicate the presence of neuro-inflammation in the central nervous system of CWP patients. Future studies should be larger and control for confounders and determine which alterations are unspecific/general and which are specific changes.Funding Agencies|Swedish Research Council [K2015-99x-21874-05-4]; Medical Research Council of Southeast Sweden [FORSS-159031]; Region Ostergotland [LIO-35923, SC-2013-00395-36]; AFA Insurance [140341]</p

Low temperature atomic hydrogen annealing of InGaAs MOSFETs

Recent work showing a strong quality improvement of the Si/SiO2 material system by low temperature atomic hydrogen annealing (AHA), and the fact that III-V semiconductors outperform Si in many applications makes the investigation of AHA on III-V/high-k interfaces to a very interesting topic. In this work, the potential of AHA as a low temperature annealing treatment of InGaAs metal-oxide-semiconductor field-effect transistors is presented and compared to conventional annealing in a rapid thermal process (RTP) system using forming gas. It is found that post metal annealing in atomic hydrogen greatly enhances the quality of the metal-oxide-semiconductor structure in terms of effective mobility, minimum subthreshold swing, and reliability. The device performance is comparable to RTP annealing but can be performed at a lower temperature, which opens up for integration of more temperature-sensitive materials in the device stack

Specific proteins of the trapezius muscle correlate with pain intensity and sensitivity - an explorative multivariate proteomic study of the trapezius muscle in women with chronic widespread pain

Chronic widespread pain (CWP) including fibromyalgia syndrome (FMS) has a high prevalence and is associated with prominent negative consequences. CWP/FMS exhibits morphological and functional alterations in the central nervous system. The importance of peripheral factors for maintaining the central alterations are under debate. In this study, the proteins from biopsies of the trapezius muscle from 18 female CWP/FMS patients and 19 healthy female controls were analyzed. Pain intensity and pressure pain thresholds (PPT) over the trapezius muscles were registered. Twelve proteins representing five different groups of proteins were important regressors of pain intensity in CWP/FMS (R-2=0.99; P amp;lt; 0.001). In the regression of PPT in CWP/FMS, it was found that 16 proteins representing six groups of proteins were significant regressors (R-2=0.95, P amp;lt; 0.05). Many of the important proteins were stress and inflammation proteins, enzymes involved in metabolic pathways, and proteins associated with muscle damage, myopathies, and muscle recovery. The altered expression of these proteins may reflect both direct and indirect nociceptive/inflammatory processes as well as secondary changes. The relative importance of the identified proteins and central alterations in CWP need to be investigated in future research. Data from this and the previous study concerning the same cohorts give support to the suggestion that peripheral factors are of importance for maintaining pain aspects in CWP/FMS.Funding Agencies|Swedish Council for Working Life and Social Research; Swedish Research Council Medical Research Council of Southeast Sweden; AFA Insurance</p

Optimization of Near-Surface Quantum Well Processing

Herein, an optimized process flow of near-surface quantum well metal–oxide–semiconductor field-effect transistors (MOSFETs) based on planar layers of metalorganic vapor-phase epitaxy (MOVPE) grown InxGa1−xAs is presented. It is found that by an optimized pre-growth cleaning and post-metal anneal, the quality of the MOS structure can be greatly enhanced. This optimization is a first step toward realization of a scalable platform for topological qubits based on a well-defined network of lateral InxGa1−xAs nanowires grown by selective area growth

http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-88080 Identification of Proteins from Interstitium of Trapezius Muscle in Women with Chronic Myalgia Using Microdialysis in Combination with Proteomics

Background: Microdialysis (MD) of the trapezius muscle has been an attractive technique to investigating small molecules and metabolites in chronic musculoskeletal pain in human. Large biomolecules such as proteins also cross the dialysis membrane of the catheters. In this study we have applied in vivo MD in combination with two dimensional gel electrophoresis (2-DE) and mass spectrometry to identify proteins in the extracellular fluid of the trapezius muscle. Materials and Methods: Dialysate from women with chronic trapezius myalgia (TM; n = 37), women with chronic wide spread pain (CWP; n = 18) and healthy controls (CON; n = 22) was collected from the trapezius muscle using a catheter with a cut-off point of 100 kDa. Proteins were separated by two-dimensional gel electrophoresis and visualized by silver staining

Strained Inx Ga(1-x )As/InP near surface quantum wells and MOSFETs

We present electronic band structure properties of strained InxGa(1-x)As/InP heterostructure near surface quantum wells oriented in the (100) crystallographic direction using eight-band k · p theory, which are further parameterized by an energy level, effective mass, and nonparabolicity factor. The electronic band structure parameters are studied for the well composition of 0.2 ≤ x ≤ 1 and thickness from 5 to 13 nm. The bandgap and effective mass of the strained wells are increased for x >0.53 due to compression strain and decreased for x < 0.53 due to tensile strain as compared to that of unstrained wells. The calculated band structure parameters are utilized in modeling long channel In0.71Ga0.29As/InP quantum well MOSFETs, and the model is validated against measured I-V and low frequency C-V characteristics at room temperature and cryogenic temperature. Exponential band tails and first- and second-order variation of the charge centroid capacitance and interface trap density are included in the electrostatic model. The Urbach parameter obtained in the model is E0 = 9 meV, which gives subthreshold swing (SS) of 18 mV/dec at T = 13 K and agrees with the measured SS of 19 mV/dec. Interface trap density is approximately three orders higher at T = 300 K compared to T = 13 K due to multi-phonon activated traps. This model emphasizes the importance of considering disorders in the system in developing device simulators for cryogenic applications

Template-Assisted Selective Epitaxy of InAs on W

Results on integration of InAs on W films through template assisted selective epitaxy are presented. The InAs crystals are analysed using SEM, electron beam backscattering and in-situ electrical measurements. A high yield of single crystalline InAs can be obtained for certain template diameters and pitches which demonstrates that this is a viable route to integrate III-V semiconductors in the back-end-of-line of CMOS circuits for added functionality