Design and Characterization of 5 µm Pitch InGaAs Photodiodes Using In Situ Doping and Shallow Mesa Architecture for SWIR Sensing.

This paper presents the complete design, fabrication, and characterization of a shallow-mesa photodiode for short-wave infra-red (SWIR) sensing. We characterized and demonstrated photodiodes collecting 1.55 µm photons with a pixel pitch as small as 3 µm. For a 5 µm pixel pitch photodiode, we measured the external quantum efficiency reaching as high as 54%. With substrate removal and an ideal anti-reflective coating, we estimated the internal quantum efficiency as achieving 77% at 1.55 µm. The best measured dark current density reached 5 nA/cm2 at -0.1 V and at 23 °C. The main contributors responsible for this dark current were investigated through the study of its evolution with temperature. We also highlight the importance of passivation with a perimetric contribution analysis and the correlation between MIS capacitance characterization and dark current performance.

Size and Solvation Effects on Electronic and Optical Properties of PbS Quantum Dots.

PbS quantum dots (QDs), among the most mature nanocrystals obtained by colloidal chemistry, are promising candidates in optoelectronic applications at various operational frequencies. QD device performances are often determined by charge transport, either carrier injection before photoemission or charge detection after photoabsorption, which is significantly influenced by the dielectric environment. Here, we present the electronic structure and the optical gap of PbS QDs versus size for various solvents calculated using ab initio methods including the many-body perturbation approaches. This study highlights the importance of the dielectric environment, pointing out (1) the non-negligible shift of the electronic structure due to the ground state polarization and (2) a substantial impact on the electronic bandgap. The electron-hole binding energy, which varies largely with the QD size and solvent, is well-described by an electrostatic model. This study reveals the fundamental physics of size and solvation effects, which could be useful to design PbS QD-based optoelectronic devices.

The complex optical index of PbS nanocrystal thin films and their use for short wave infrared sensor design.

As nanocrystals (NCs) gain maturity, they become central building blocks for optoelectronics in devices such as solar cells and, more recently, infrared focal plane arrays. Now that the proof of concept of these devices has been established, their optimization requires a deeper understanding of their electronic and optical features to engineer their optoelectronic properties accurately. Though PbS NCs have been extensively investigated, the complex optical index of PbS NC thin films remains mostly unknown. Some previous works have unveiled the optical index for this type of material optimized for solar cells (excitonic peak at 940 nm), but longer wavelengths remain scarce and surface chemistry effects, which are known to be of central importance for layer doping, are simply unexplored. Here, we conduct a systematic investigation of the complex optical index of PbS NC thin films using broadband spectrally resolved ellipsometry. The obtained results are then compared with simulations combining tight-binding (TB) modeling at the NC level and the Bruggeman model to expand the results to the film scale. While TB calculation gives the NC optical indices, we extract the key NC film parameters such as the NC volume fraction and ligand indices by fitting the Bruggeman formula to ellipsometry measurements. We also bring evidence that this joint modeling method can be conducted without the need for ellipsometry data while preserving the main feature of the experimental results. Finally, the unveiled optical indices are used to model the absorption of short-wave infrared diode stacks based on PbS NCs and are relevant for state-of-the-art devices. Our electromagnetic modeling shows that the absorption within the contact is now a major limitation of the current device operated at the telecom wavelength.

Egalitarianism and Sexual Prejudice: the Role of Ingroup Distinctiveness Motives.

The present research examined the hypothesis that heterosexual men's motivation to differentiate their ingroup from gay men moderates the link between egalitarianism and sexual prejudice. In two experiments conducted in Switzerland (N = 74) and Ecuador (N = 104), we assessed heterosexual men's endorsement of egalitarian values and experimentally manipulated scientific evidence supporting or refuting the existence of biological differences between heterosexual and gay men (the biological theory). The main dependent variable was attitude towards homosexuality. As predicted, the interaction between egalitarianism and the biological theory was significant in both experiments, t(67) = 3.18, p = .002, ηp 2 = .13, and t(100) = 2.26, p = .026, ηp 2 = .04, respectively. Egalitarianism increased positive attitudes towards homosexuality only when science supported the existence of biological differences between heterosexual and gay men. We discuss the relevance of this finding to intergroup relations.

The student-institution fit at university: interactive effects of academic competition and social class on achievement goals.

As compared to continuing-generation students, first-generation students are struggling more at university. In the present article, we question the unconditional nature of such a phenomenon and argue that it depends on structural competition. Indeed, most academic departments use harsh selection procedure all throughout the curriculum, fostering between-student competition. In these departments, first-generation students tend to suffer from a lack of student-institution fit, that is, inconsistencies with the competitive institution's culture, practices, and identity. However, one might contend that in less competitive academic departments continuing-generation students might be the ones experiencing a lack of fit. Using a cross-sectional design, we investigated the consequences of such a context- and category-dependent lack of fit on the endorsement of scholastically adaptive goals. We surveyed N = 378 first- and continuing-generation students from either a more competitive or a less competitive department in their first or final year of bachelor's study. In the more competitive department, first-to-third year decrease of mastery goals (i.e., the desire to learn) was found to be steeper for first- than for continuing-generation students. In the less competitive department, the reversed pattern was found. Moreover, first-to-third year decrease of performance goals (i.e., the desire to outperform others) was found to be steeper within the less competitive department but did not depend on social class. This single-site preliminary research highlights the need to take the academic context into account when studying the social class graduation gap.

Egalitarianism and sexual prejudice: the role of ingroup distinctiveness motives

The present research examined the hypothesis that heterosexual men's motivation to differentiate their ingroup from gay men moderates the link between egalitarianism and sexual prejudice. In two experiments conducted in Switzerland (N = 74) and Ecuador (N = 104), we assessed heterosexual men's endorsement of egalitarian values and experimentally manipulated scientific evidence supporting or refuting the existence of biological differences between heterosexual and gay men (the biological theory). The main dependent variable was attitude towards homosexuality. As predicted, the interaction between egalitarianism and the biological theory was significant in both experiments, t(67) = 3.18, p = .002, ηp 2 = .13, and t(100) = 2.26, p = .026, ηp 2 = .04, respectively. Egalitarianism increased positive attitudes towards homosexuality only when science supported the existence of biological differences between heterosexual and gay men. We discuss the relevance of this finding to intergroup relations (AU)

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Performance goals in conflictual social interactions: towards the distinction between two modes of relational conflict regulation.

Socio-cognitive conflict has been defined as a situation of confrontation with a disagreeing other. Previous research suggests that individuals can regulate conflict in a relational way, namely by focusing on social comparison between relative levels of competences. Relational conflict regulation has been described as yielding particularly negative effects on social interactions and learning, but has been understudied. The present research addresses the question of the origin of relational conflict regulation by introducing a fundamental distinction between two types of regulation, one based on the affirmation of one's own point of view and the invalidation of the other's (i.e., 'competitive' regulation), the other corresponding to the protection of self-competence via compliance (i.e., 'protective' regulation). Three studies show that these modes of relational conflict regulation result from the endorsement of distinct performance goals, respectively, performance-approach goals (trying to outperform others) and performance-avoidance goals (avoiding performing more poorly than others). Theoretical implications for the literature on both conflict regulation and achievement goals are discussed.

Three-dimensional multiple-order twinning of self-catalyzed GaAs nanowires on Si substrates.

In this paper we introduce a new paradigm for nanowire growth that explains the unwanted appearance of parasitic nonvertical nanowires. With a crystal structure polarization analysis of the initial stages of GaAs nanowire growth on Si substrates, we demonstrate that secondary seeds form due to a three-dimensional twinning phenomenon. We derive the geometrical rules that underlie the multiple growth directions observed experimentally. These rules help optimizing nanowire array devices such as solar or water splitting cells or of more complex hierarchical branched nanowire devices.

Social influence and threat in confrontations between competent peers.

Five studies investigated social influence processes in confrontations between competent peers and showed a default absence of influence of a competent source on an equally competent target. This default lack of influence is attributed to the representation that competent targets give to the influence encounter, in which different answers from competent peers are incompatible, the error of the source thus being the sine qua non condition of targets' correctness. However, an influence appeared when the representation of the task was modified via a decentering procedure (Study 1), even when controlling for alternative explanations (Study 2). Study 3 demonstrated that this liberating effect of decentering did not appear when the source was incompetent. Study 4 also examined social comparison processes and showed that independence of judgments produced the same liberating effect as decentering. Finally, Study 5 showed that the default lack of influence in confrontations between competent peers is due to the presence of a threat to the self. Indeed, the reduction of threat through a procedure of self-affirmation modified the representation of the task and allowed influence to appear.

"I'm not gay. . . . I'm a real man!": Heterosexual Men's Gender Self-Esteem and Sexual Prejudice.

Five studies examined the hypothesis that heterosexual men, but not heterosexual women, endorse negative attitudes toward homosexuality (i.e., sexual prejudice) in order to maintain a positive gender-related identity that is unambiguously different from a homosexual identity. Studies 1 and 2 showed that men's (but not women's) gender self-esteem (but not personal self-esteem) was positively related to sexual prejudice: The more positive heterosexual men's gender self-esteem, the more negative their attitude toward homosexuality. Studies 3 and 4 showed that this link appears specifically among men motivated to maintain psychological distance from gay men. Study 5 experimentally manipulated the perceived biological differences between homosexual and heterosexual men. The previously observed link between men's gender self-esteem and sexual prejudice appeared in the control and no-differences conditions but disappeared in the differences condition. These findings are discussed in terms of men's attitudes as a defensive function against threat to masculinity.

The coordination of problem solving strategies: when low competence sources exert more influence on task processing than high competence sources.

Previous research has shown that low competence sources, compared to highly competent sources, can exert influence in aptitudes tasks in as much as they induce people to focus on the task and to solve it more deeply. Two experiments aimed at testing the coordination between self and source's problem solving strategies as a main explanation of such a difference in influence. The influence of a low versus high competence source has been examined in an anagram task that allows for distinguishing between three response strategies, including one that corresponds to the coordination between the source's strategy and participants' own strategy. In Study 1 the strategy suggested by the source was either relevant and useful or irrelevant and useless for solving the task. Results indicated that participants used the coordination strategy in a larger extend when they had been confronted to a low competence rather than a highly competent source but only when the source displayed a strategy that was useful to solve the task. In Study 2 the source's strategy was always relevant and useful, but a decentring procedure was introduced for half of the participants. This procedure induced participants to consider other points of view than their own. Results replicated the difference observed in Study 1 when no decentring was introduced. The difference however disappeared when decentring was induced, because of an increase of the high competence source's influence. These results highlight coordination of strategies as one mechanism underlying influence from low competence sources.

Being similar versus being equal: intergroup similarity moderates the influence of in-group norms on discrimination and prejudice.

In two studies, we examined the influence of in-group norms of anti- and pro-discrimination on prejudice and discrimination as a function of intergroup similarity (Studies 1 and 2) and in-group identification (Study 2). In a condition where there was no information about intergroup similarity (Study 1) or intergroup similarity was low (Study 2), prejudice and discrimination were lower when norms prescribe anti-discrimination compared to pro-discrimination. In contrast, when intergroup similarity was high, prejudice and discrimination were higher when the in-group norm represents anti-discrimination compared to pro-discrimination. This pattern was most apparent among highly identified in-group members (Study 2). The paradoxical effect of the anti-discrimination norm in the high similarity condition is interpreted as a response to the threat this situation introduces to in-group distinctiveness.

Performance-approach and performance-avoidance goals: when uncertainty makes a difference.

Performance-avoidance goals (the desire to avoid performing more poorly than others do) have been shown to have consistently deleterious effects on performance but the effects of performance-approach goals (trying to outperform others) are more complex. Two studies examine uncertainty as a moderator of the effect of performance-approach goals on performance. Experiment 1 shows that manipulated performance-approach goals lead to better performance than do performance-avoidance goals in the absence of uncertainty about performance but when participants learn that a coactor disagreed with them about problem solutions, creating uncertainty, performance-approach goals do not differ from performance-avoidance goals in their effect on performance. Experiment 2 shows that uncertainty also moderates the effects of self-set performance-approach goals. Moreover, the same dynamic occurs with another kind of uncertainty: negative competence feedback.