Electron Injection-induced Effects In Iii-nitrides: Physics And Applications

This research investigated the effect of electron injection in III-Nitrides. The combination of electron beam induced current and cathodoluminescence measurements was used to understand the impact of electron injection on the minority carrier transport and optical properties. In addition, the application of the electron injection effect in optoelectronic devices was investigated. The impact of electron injection on the minority carrier diffusion length was studied at various temperatures in Mg-doped p-GaN, p-Al[subscript x]Ga[subscript 1-x]N, and p-Al[subscript x]Ga[subscript 1-x] N/GaN superlattices. It was found that Lsubscript n] experienced a multi-fold linear increase and that the rate of change of L[subscript n] decreased exponentially with increasing temperature. The effect was attributed to a temperature-activated release of the electrons, which were trapped by the Mg levels. The activation energies, E[subscript a], for the electron injection effect in the Mg-doped (Al)GaN samples were found to range from 178 to 267 meV, which is close to the thermal ionization energy of the Mg acceptor. The E[subscript a] observed for Al[subscript 0.15]Ga[subscript 0.85]N and Al[subscript 0.2]Ga[subscript 0.8]N was consistent with the deepening of the Mg acceptor level due to the incorporation of Al into the GaN lattice. The E[subscript a] in the homogeneously doped Al[subscript 0.2]Ga[subscript 0.8]N/GaN superlattice indicates that the main contribution to the electron injection effect comes from the capture of injected electrons by the wells (GaN). The electron injection effect was successfully applied to GaN doped with an impurity (Mn) other than Mg. Electron injection into Mn-doped GaN resulted in a multi-fold increase of the L[subscript n] and a pronounced decrease in the band-to-band cathodoluminescence intensity. The E[subscript a] due to the electron injection effect was estimated from temperature-dependent cathodoluminescence measurements to be 360 meV. The decrease in the band-to-band cathodoluminescence is consistent with an increase in L[subscript n] and these results are attributed to an increase in the minority carrier lifetime due to the trapping of injected electrons by the Mn levels. A forward bias was applied to inject electrons into commercially built p-i-n and Schottky barrier photodetectors. Up to an order of magnitude increase in the peak (360 nm) responsivity was observed. The enhanced photoresponse lasted for over four weeks and was attributed to an electron injection-induced increase of L[subscript n] and the lifetime

Study of temperature dependence for the electron injection-induced effects in GaN

Electron-beam injection-induced increase of minority carrier diffusion length in p-type GaN was studied as a function of sample temperature ranging from 25 degreesC to 130 degreesC. It was found that the rate for diffusion length increase exponentially decays with increasing temperature. This decay was attributed to a temperature-activated release of electron-beam injected electrons trapped on Mg levels. The activation energy of these levels was found to be similar to178 meV. This is in good agreement with the previously reported position for Mg levels in the GaN band gap

The Method of Moments and the Energy Levels of Molecules and Solids

The method of moments is used to derive the energy levels of a representative series of molecules, crystalline and noncrysta-1- line solids. It provides a direct link between the density of states of the eigenvalue spectrum and the connectivity and topology of the molecular or solid state network

Cathodoluminescence studies of the electron injection-induced effects in GaN

Local irradiation of p-type GaN with the electron beam of a scanning electron microscope resulted in up to a threefold decrease of the peak cathodoluminescence intensity at similar to379 nm, as was observed in the variable temperature measurements. The cathodoluminescence results are consistent with an increase of the minority carrier diffusion length in the material, as is evident from the electron-beam-induced current measurements. The activation energy for the electron injection effect, estimated from the temperature-dependent cathodoluminescence, is in agreement with the thermal ionization energy of the Mg-acceptor in GaN

Electron injection-induced effects in Mn-doped GaN

Electron injection into Mn-doped GaN resulted in pronounced changes in the minority carrier diffusion length and cathodoluminescence. In particular, multiple-fold decrease of the band-to-band cathodoluminescence intensity was observed in the temperature between -50 and 80degreesC. This decrease was accompanied by an increase of the minority carrier diffusion length in the material, measured by electron-beam-induced current. Temperature-dependent cathodoluminescence measurements revealed a recovery of the cathodoluminescence intensity with an activation energy of 360 meV

CHESHIRE (Reino Unido) (Inglaterra). Mapas generales (1794). 1:136000

Escala gráfica de 12 millas estatutarias [= 14,2 cm]. Coordenadas referidas al meridiano de Londres (O 3°25'--O 1°39°/N 53°36'--N 53°00'). Recuadro geográfico de 5' en 5'. Figura trazado el meridiano de Chester. OrientadoOrografía a trazosTabla de signos convencionales para indicar las ciudades, parroquias, lagos, molinos, caminos, límites entre "hundreds", etc.Forma parte de la Colección Mendoz

CHESHIRE (Reino Unido) (Inglaterra). Mapas generales (1794). 1:65000

Dedicatoria : "By Permission to His Royal Highness, George, Prince of Wales, Duke of Cornwall & Roshsay, and Earl of Chester &c. &c. This Survey of the County Palatine of Chester, is most humbly Dedicated, by His Royal Highnefs's most Devoted Servant P.P. Burdett"Título redactado a partir del contenido del documentoEscala gráfica de 6 millas [= 14,9 cm]. Coordenadas referidas al meridiano de Londres (O 3°23'30''--O 1°44'20''/N 53°39'20''--N 52°59'55''). Recuadro geográfico de 5' en 5'. Orientado con lis en rosa de ocho vientosOrografía a trazosTabla de signos convencionales para indicar ciudades, parroquias, molinos, límites entre "hundreds", etc.Dedicatoria enmarcada en cartela decorada con motivos vegetalesForma parte de la Colección MendozaInserta : "The Series of great triangles reduce to an Horizontal Plane" ; "A Plan of the City of Chester". Escala [ca. 1:6800], 600 yardas [= 8,1 cm

Evaluation of the Onset of Protective Immunity from Administration of a Modified-live, Non-adjuvanted Vaccine prior to Intranasal Challenge with Bovine Herpesvirus-1

Study objectives were to determine if subcutaneous administration of a modified-live, non-adjuvanted vaccine containing bovine herpesvirus-1 (BHV-1) at five, three, or two days pre-challenge, would reduce clinical signs, rectal temperatures, and viral shedding, and enhance serological response to BHV-1. Colostrumdeprived, neonatal calves (n = 48) were randomly assigned to six treatment groups, each containing eight calves. Treatment groups were based on administration of vaccine (VAC) or saline controls (CON) and day of administration (day -5, -3 or -2) relative to intranasal BHV-1 challenge (day 0). Following challenge, calves were monitored for clinical signs, rectal temperature, seroconversion, and quantity of BHV-1 recovered by virus isolation from nasal swabs. Data for the evaluation period (days 4-14) were analyzed using multivariable statistics. Day -5 and -3 VAC groups had fewer (P \u3c 0.05) days of clinical illness compared to CON. Rectal temperatures were lower (P \u3c 0.05) during days 4-8 for each of the VAC groups as compared to combined CON groups. CON calves shed BHV-1 for more days than calves vaccinated on day -5 (P \u3c 0.01), day -3 (P = 0.06), or day -2 (P = 0.06). Mean concentrations of nasal BHV-1 also differed (P \u3c 0.05) between combined CON groups and each of the VAC groups during at least one study day. Calves in the VAC groups (median = 10 days) seroconverted to BHV-1 (P \u3c 0.01) sooner than CON calves (median = 14 days). This study demonstrated that the use of a non-adjuvanted MLV vaccine in neonatal calves can reduce the effects of BHV-1 challenge soon after vaccination

Vegetation change(1988-2010) in Camdeboo national park (South Africa) using fixed-point photo monitoring: the role of herbivory and climate

Fixed-point photo monitoring supplemented by animal census data and climate monitoring potential has never been explored as a long-term monitoring tool for studying vegetation change in the arid and semi-arid national parks of South Africa. The long-term (1988–2010), fixed-point monitoring dataset developed for the Camdeboo National Park, therefore, provides an important opportunity to do this. Using a quantitative estimate of the change in vegetation and growth form cover in 1152 fixed-point photographs, as well as series of step-point vegetation surveys at each photo monitoring site, this study documented the extent of vegetation change in the park in response to key climate drivers, such as rainfall, as well as land use drivers such as herbivory by indigenous ungulates. We demonstrated the varied response of vegetation cover within three main growth forms (grasses, dwarf shrubs [ 1 m]) in three different vegetation units and landforms (slopes, plains, rivers) within the Camdeboo National Park since 1988. Sites within Albany Thicket and Dwarf Shrublands showed the least change in vegetation cover, whilst Azonal vegetation and Grassy Dwarf Shrublands were more dynamic. Abiotic factors such as drought and flooding, total annual rainfall and rainfall seasonality appeared to have the greatest influence on growth form cover as assessed from the fixed-point photographs. Herbivory appeared not to have had a noticeable impact on the vegetation of the Camdeboo National Park as far as could be determined from the rather coarse approach used in this analysis and herbivore densities remained relatively low over the study duration. Conservation implications: We provided an historical assessment of the pattern of vegetation and climatic trends that can help evaluate many of South African National Parks’ biodiversity monitoring programmes, especially relating to habitat change. It will help arid parks in assessing the trajectories of vegetation in response to herbivory, climate and management interventions

Screening and techno-economic assessment of biomass-based power generation with CCS technologies to meet 2050 CO2 targets

Biomass-based power generation combined with CO2 capture and storage (Biopower CCS) currently represents one of the few practical and economic means of removing large quantities of CO2 from the atmosphere, and the only approach that involves the generation of electricity at the same time. We present the results of the Techno-Economic Study of Biomass to Power with CO2 capture (TESBiC) project, that entailed desk-based review and analysis, process engineering, optimisation as well as primary data collection from some of the leading pilot demonstration plants. From the perspective of being able to deploy Biopower CCS by 2050, twenty-eight Biopower CCS technology combinations involving combustion or gasification of biomass (either dedicated or co-fired with coal) together with pre-, oxy- or post-combustion CO2 capture were identified and assessed. In addition to the capital and operating costs, techno-economic characteristics such as electrical efficiencies (LHV% basis), Levelised Cost of Electricity (LCOE), costs of CO2 captured and CO2 avoided were modelled over time assuming technology improvements from today to 2050. Many of the Biopower CCS technologies gave relatively similar techno-economic results when analysed at the same scale, with the plant scale (MWe) observed to be the principal driver of CAPEX (£/MWe) and the cofiring % (i.e. the weighted feedstock cost) a key driver of LCOE. The data collected during the TESBiC project also highlighted the lack of financial incentives for generation of electricity with negative CO2 emissions