Magneto-optical confirmation of Landau level splitting in a GaN/AlGaN 2DEG grown on bulk GaN

Landau level splitting in a two-dimensional electron gas (2DEG) confined in an ultrapure GaN/AlGaN heterostructure grown by molecular beam epitaxy on bulk GaN is verified spectroscopically. The Landau level fan reconstructed from magneto-photoluminescence (PL) data yields an effective mass of 0.24m₀ for the 2D electrons. Narrow excitonic PL line widths < 100 μeV, an atomically flat surface of the layer stack, as well as the absence of the 2DEG in the dark environment, are important ancillary experimental findings while focusing on magneto-PL investigations of the heterostructure. Simultaneously recorded Shubnikov-de Haas and magneto-PL intensity oscillations under steady UV illumination exhibit an identical frequency and allow for two independent ways of determining the 2D density

Carbon-doped MBE GaN: Spectroscopic insights

The predicted acceptor impurity nature of carbon in hexagonal GaN grown by molecular-beam epitaxy (MBE) is revisited spectroscopically in the energy range between 1.6 and 3.5 eV. Photoluminescence (PL) spectra from ultra-pure GaN and material doped with carbon at a level of 1·18 cm⁻³ differ significantly in the energy range between 3.0 and 3.3 eV depending on the Ga/N stoichiometry during MBE growth. Acceptor-like features formerly attributed to carbon, beryllium or magnesium incorporation are found for both, undoped and carbon-doped GaN. The intensity of these features depends on the Ga/N stoichiometry during growth. While for Ga-lean surface regions, exhibiting multiple 10 nm deep pits, the observed PL features are found to be less intense compared to Ga-rich surface regions, the situation reverses for carbon-doped material. For all samples, the intensity of the yellow luminescence band around 2.2 eV is weak. The results point at crystal defects and the unintentionally present oxygen as the origin of the spectroscopic features traditionally attributed to carbon in GaN

Voting as a Signaling Device

In this paper, citizens vote in order to influence the election outcome and in order to signal their unobserved characteristics to others. The model is one of rational voting and generates the following predictions: (i) The paradox of not voting does not arise, because the benefit of voting does not vanish with population size. (ii) Turnout in elections is positively related to the importance of social interactions. (iii) Voting may exhibit bandwagon effects and small changes in the electoral incentives may generate large changes in turnout due to signaling effects. (iv) Signaling incentives increase the sensitivity of turnout to voting incentives in communities with low opportunity cost of social interaction, while the opposite is true for communities with high cost of social interaction. Therefore, the model predicts less volatile turnout for the latter type of communities

Mikrobaugruppen mechanisch prüfen

The reliability of mirco-electronical and micro-mechanical components and assembly groups is considered. The deformation analysis by means of laser methods is determined. Examples are given e.g. the glob top problem (thermal behaviour of electronic encapsulation). Vibration analysis of PCB is presented also using laser metrology. Thermo-mechanical analysis of micro-components is carried out

Modulare Mikrosysteme aus dem Baukasten

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