Surface morphology of AlGaN/GaN heterostructures grown on bulk GaN by MBE

In this report the influence of the growth conditions on the surface morphology of AlGaN/GaN heterostructures grown on sapphire-based and bulk GaN substrates is nondestructively investigated with focus on the decoration of defects and the surface roughness. Under Ga-rich conditions specific types of dislocations are unintentionally decorated with shallow hillocks. In contrast, under Ga-lean conditions deep pits are inherently formed at these defect sites. The structural data show that the dislocation density of the substrate sets the limit for the density of dislocation-mediated surface structures after MBE overgrowth and no noticeable amount of surface defects is introduced during the MBE procedure. Moreover, the transfer of crystallographic information, e.g. the miscut of the substrate to the overgrown structure, is confirmed. The combination of our MBE overgrowth with the employed surface morphology analysis by atomic force microscopy (AFM) provides a unique possibility for a nondestructive, retrospective analysis of the original substrate defect density prior to device processing

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

Public opinion polls, voter turnout, and welfare: An experimental study

We experimentally study the impact of public opinion poll releases on voter turnout and welfare in a participation game. We find higher overall turnout rates when polls inform the electroate about the levels of support for the candidates than when polls are prohibited. Distinguishing between allied and floating voters, our data show that this increase in turnout is entirely due to floating voters. When polls indicate equal levels of support for the candidates, turnout is high and welfare is low (compared to the situation without polls). In contrast, when polls reveal more unequal levels of support, turnout is lower with than without this information, while the effect of polls on welfare is nonnegative. Finally, many of our results are well predicted by quantal response (logit) equilibrium

Neighborhood information exchange and voter participation: an experimental study

We study the effect of social embeddedness on voter turnout by investigating the role of information about other voters' decisions. We do so in a participation game, in which we distinguish between early and late voters. Each late voter is told about one early voter's turnout decision. Cases are distinguished where the voters are allies (support the same group) or adversaries (with opposing preferences) and where they are uncertain about each other's preferences. Our experimental results show that the social embeddedness matters: this information increases aggregate turnout by approximately 50%. The largest effect is observed for allies. Early voters strategically try to use their first mover position and late voters respond to this

Qualitätsprüfung in der Glasindustrie

An optical, nondestructive measuring process using laser technology. Presentday requirements applicable to the surface of special types of glass call for a non-destructive measuring technique. With very low contact forces, this cannot be achieved with conventional, tactile measuring systems. Here, the potential of optical measuring systems for non-destructive measuring purposes is presented with reference to two industrial applications, namely the quality testing of display window glass and the ultra-precise measurement of mirrors

Quantification of void defects on PERC solar cell rear contacts

Passivated emitter and rear (PERC) solar cells can show void formation within their metallized local rear contact. It is known that voids can cause enhanced rear side recombination. In this work, we present a study on void related current losses and the correlation to the local Al-doped silicon layer which forms the back-surface field (BSF) at the rear contact. At first, void related current losses have been quantitatively evaluated. By further microstructural investigation at lengthwise prepared rear contacts, a method for the analysis of BSF thickness distribution was developed. It turned out that BSFs within voids can vanish on both, small and large length scales. Regions with voids can be well passivated and result therefore in negligible current losses. The presented approach allows the quantitatively assessment of PERC solar cell rear contacts in terms of total current losses and void ratio