Optical Properties of Wurtzite InN and Related Alloys

In dieser Arbeit werden die optischen Eigenschaften von Wurtzitstruktur InN und verwandten ternären InGaN und AlInN, sowie quaternären AlInGaN Legierungen untersucht. Der Schwerpunkt wird auf die Charakterisierung mittels spektroskopischer Ellipsometrie gelegt. Die auf Si(111) Substraten gewachsenen InN-Proben und die Kohlstoff dotierten InN-Proben sind im Spektralbereich vom mittleren Infrarot bis hin zum Vakuum-Ultraviolett untersucht worden. Die Elektronenkonzentration für die InN-Proben wird durch selbstkonsistentes Lösen (der Ellipsometriedaten Analyse im Infrarotbereich und der Anpassung des Absorption Ansatz) bestimmt. Die intrinsische spannungsfreie Bandlücke für InN Proben wird unter Berücksichtigung von Vielteilcheneffekten wie der Bandlückenrenormierung und der Burstein-Moss-Verschiebung, sowie dem Einfluss der Verzerrung für die Bandlücke bestimmt. Die k*p-Methode wird verwendet, um die Verschiebung der Bandlücke (beeinflusst durch Verzerrung) zu berechnen. Es wird demonstriert, dass eine Erhöhung des Kohlenstofftetrabromid (CBr4) Drucks während des Wachstumsprozess, die Elektronenkonzentration in den InN-Proben erhöht. Die Indium-verwandten Legierungen wurden im Spektralbereich des nahen Infrarot bis zum Vakuum-Ultraviolett untersucht. Das analytische Modell, der dielektrichen Funktion im Spektralbereich 1-10 eV, für die Indium-verwandte Legierungen wird präsentiert. Durch die Anpassung des analytischen Modells an die experimentellen dielektrischen Funktionen, werden die Bandlücke und die Übergangsenergien im Hochenergie-Bereich evaluiert. Die Bowing-Parameter der spannungsfreien Bandlücke für die ternären Systeme InGaN und AlInN werden bestimmt. Es wird demonstriert, dass der Bowing-Parameter für AlInN von der Komposition der Legierung abhängig ist. Die Kenntnis von Bowing-Parametern für die ternären Legierungen ermöglicht die Entwicklung einer empirischen Gleichung, zur Berechnung der Bandlücke in quaternären Legierungen. Alle experimentell durch Ellipsometrie bestimten Bandlücken der untersuchten Legierungen werden durch ab-initio Daten unterstützt.In this work, optical properties of wurtzite structure InN and related ternary InGaN and AlInN, as well as quaternary AlInGaN alloys were investigated. The spectroscopic ellipsometer was used as the main characterization tool for the analysis of the optical properties. The InN samples grown on Si(111) substrates, as well as carbon doped InN samples were investigated from mid-infrared up to vacuum-ultraviolet spectral range. The electron concentration for InN samples were evaluated by solving a self-consistent problem that includes the IR-SE ellipsometry data analysis and the imaginary dielectric function around the band gap calculation. The intrinsic strain-free band-gap was estimated after taking into consideration a band-gap renormalization and Burstein-Moss shift, as well as a strain influence on the band gap. The k*p method was used to calculate the strain induced band-gap shift. From the analysis, it was shown that for the carbon doped InN samples the electron concentration increases linearly by increasing the CBr4 dopant pressure during the MBE growth process. The In-related alloys were investigated from near-infrared up to vacuum-ultraviolet spectral range. The analytical model of the dielectric function in the spectral range 1-10 eV was presented. From the fit of the analytical model to the experimental dielectric functions, the band gaps and high-energy inter-band transitions were estimated. The strain-free band-gap bowing parameters for ternary InGaN and AlInN alloys were obtained. It was demonstrated, that the bowing parameter for AlInN is composition dependent. With the knowledge of the bowing parameters of ternary alloys, it was possible to develop an empirical equation that allows to estimate the band gap for a quaternary AlInGaN alloy. All experimentally obtained band gaps are in good agreement with the ab-initio calculated values

Luminescence from two-dimensional electron gases in InAlN/GaN heterostructures with different In content

The luminescence properties of InxAl1−xN/GaN heterostructures are investigated systematically as a function of the In content (x = 0.067 − 0.208). The recombination between electrons confined in the two-dimensional electron gas and free holes in the GaN template is identified and analyzed. We find a systematic shift of the recombination with increasing In content from about 80 meV to only few meV below the GaN exciton emission. These results are compared with model calculations and can be attributed to the changing band profile and originating from the polarization gradient between InAlN and GaN

Sėjamosios : mokymo priemonė Žemės ūkio universiteto studentams

Bibliogr.: p. 45 ( 10 pavad.)Vytauto Didžiojo universitetasŽemės ūkio akademij

The Role of Clusters in the Innovation and Performance of the Small and Medium-Sized Technology Enterprises in Europe

The cluster impact on innovation and performance of SMEs has attracted considerable attention in the literature. However, there are still several knowledge gaps in this area and further research is required to fill those gaps. We constructed a multi dimensional theoretical model which involves different factors of cluster characteristics, firm’s inner capabilities, third parties role, and external relationships. We tested the theoretical model empirically by collecting a sample from technology SMEs belonging to clusters within the European Union. The data were analyzed using SmartPLS software. The study tends to support the importance of social networking and learning orientation for firm’s innovativeness. Furthermore, our study highlights a positive effect of geographical proximity between firms for SMEs’ performance

The Role of Clusters in the Innovation and Performance of the Small and Medium-Sized Technology Enterprises in Europe

The cluster impact on innovation and performance of SMEs has attracted considerable attention in the literature. However, there are still several knowledge gaps in this area and further research is required to fill those gaps. We constructed a multi dimensional theoretical model which involves different factors of cluster characteristics, firm’s inner capabilities, third parties role, and external relationships. We tested the theoretical model empirically by collecting a sample from technology SMEs belonging to clusters within the European Union. The data were analyzed using SmartPLS software. The study tends to support the importance of social networking and learning orientation for firm’s innovativeness. Furthermore, our study highlights a positive effect of geographical proximity between firms for SMEs’ performance

Šiuolaikinė kraštovaizdžio priežiūros komunalinė technika

Vytauto Didžiojo universitetasŽemės ūkio akademij

Investigation of technological processes of winter wheat sowing in different agricultural systems

In 2005 - 2006 the trials of technological processes of winter wheat sowing using different agricultural systems were carried out in Padovinys agricultural community Marijampole region and in the farm of Egidijus Palaima in Ustukiai village Pasvalys region. The research objective was to test the introducim winter wheat seeds with the disk coulters in the hard caly ploughed and unploughed soils of various regions. Having in mind erratic meteorological weather conditions the influence of different soil tillage tec-sowing techniques was tested during the trials as will as the seed introduction depth and germination indices. The indices of seed bed preparation and seed introduction were defined by the method proposes -scientists Kritz/Hakannson that estimated the evenness of the soil tillage and seed introduction depth, the composition of the soil lumps and moisture content of the soil above the seeds, below then and at the depth of the seed introduction. The trials enabled to conclude that if you need to introduce the winter wheat seeds with disk coulters of the seeder into the hard clay loam untilled soil the harvest residue from the soil surface should be evenly introduced into the soil before sowing. When the influence of the various agricultural systems on the indjcn i introduction and germination has been estimated the conclusion was made that this influence is insignificant. Meteorological climate conditions, soil characteristics and other criteria have greater impact. In ttx m insufficient moisture content (<3%) it becomes hard, the structure of big clods form, thus the setoa a cannot always form the due seedbed and to evenly introduce the seedsVytauto Didžiojo universitetasŽemės ūkio akademij

Ražieninės sėjamosios sėjant cukrinius runkelius prispaudimo volelių tyrimai

Santr. angl., rusBibliogr.: p. 17 (15 pavad.)Vytauto Didžiojo universitetasŽemės ūkio akademij

Impact of short-term ploughless tillage on soil physical properties, winter oilseed rape seedbed formation and productivity parameters

The demonstrational short-term on-farm field experiment was carried out on silty loam soil at the agricultural farm "Gruduva" (Sakiai reg., Lithuania) in 2003-2004. The aim of investigations was to evaluate impact of ploughless soil tillage on some soil physical properties, winter oilseed rape seedbed formation and productivity parameters. Two different soil tillage systems, conventional (CT) (deep (22-24 cm) mouldboard ploughing, presowing soil levellering and soil rolling after sowing) and reduced (RTJ (disc harrowing, presowing soil rolling), were investigated. In RT conditions winter oilseed rape seedbed was formed shallowly (33.2 mm in comparison with 37.2 mm in CT), had significantly higher (20%) moisture content in seed incorporation zone (L2 layer) and better composition of soil aggregates (27% higher amount of <2 mm soil aggregates in L2 layer) than in CT. These seedbed conditions positively influenced on winter oilseed rape stand density at the beginning of vegetation. Deep ploughing (CT) of soil in autumn fiddly crushed arable layer and made extremely high amount of micro-structure up to 28%. That significantly decreased amount of water-stabie soil aggregates. In RT stubble incorporation into the shallow layers of soil prevented rapid moisture evaporation in dry weather conditions in spring and suppressed water runoff and distribution on soil surface in wet conditions before harvesting. Ploughless soil tillage mostly had positive significant influence on winter oilseed rape productivity parameters. Winler oilseed rape plants grew about 67 boughs and up to 4 thousand pods per m2 more in comparison with CT, that influenced on higher (41 %) biological yield of seedsVytauto Didžiojo universitetasŽemės ūkio akademij

Impact of immature willows stems chopping quality on the harmful emissions evaluation

The analytical review of the experimental research results of energy plants preparation, burning efficiency and the emissions of harmful substances into the air while burning these plants, is presented in this paper. After the experimental study, immature (1-2 year of growth) willow (Salix viminalis) stems chaff chopping quality were observed. In truth, use of the drum chopping equipment prepared chaff fractional composition, and there were defined and calculated immature willow stems chaff of theoretical length (from 11.8 till 61.3 mm). They were presented and compared with the experimental research results of the low power boiler efficiency and harmful emissions into the air while burning energy plants - immature willow, chopped by the drum chopper of Maral-125 combine. The test was carried out in the laboratory of the low power boiler, which is designed to burn wood, wood briquettes and large wood chaff. After determination of boiler efficiency and harmful substances (C02, CO, NO, NOx) emissions into the environment while burning different lengths of willow chaff, it was concluded that the boiler developed about 66—86% of nominal boiler power, and pollution emissions concentration into the environment was lower when willow chaff of 49.2 mm length was burnedVytauto Didžiojo universitetasŽemės ūkio akademij