Structure of ll- VI Lattice Mismatched Epilayers used for Blue-Green Lasers for Underwater Communication

Critical thickness (hc) is calculated for capped and uncapped lattice mismatched II-VIsemiconductor epilayers. Both the old equilibrium theory and the improved theory have been used.The calculated values are compared with the experimental data on epilayers of several II-VIsemiconductors and alloys. The observed values of hc are larger than the calculated values. Howeverthe discrepancy is much smaller than that found in InGaAs/GaAs and GeSilSi layers. Moreover ascompared to InGaAs/GaA.s:a nd GeSilSi layers, the experimental data show a much smaller scatter andcan be fitted with one curve. Strain relaxation in layers with thickness h > hc is also calculated. Strainrelaxation in ZnSe layers grown on (100) GaAs shows good agreement with the equilibrium theory. Inother cases the observed relaxation is sluggish, the residual strain is larger than its calculated value.Thick highly mismatched layers behave differently. The residual strain agrees with theory anddislocations are distributed periodically, A model to interpret these observations is suggested.Implications of this study on the stability of 11V- I strained layers are discussed

Fracture model with variable range of interaction

We introduce a fiber bundle model where the interaction among fibers is modeled by an adjustable stress-transfer function which can interpolate between the two limiting cases of load redistribution, the global and the local load sharing schemes. By varying the range of interaction several features of the model are numerically studied and a crossover from mean field to short range behavior is obtained. The properties of the two regimes and the emergence of the crossover in between are explored by numerically studying the dependence of the ultimate strength of the material on the system size, the distribution of avalanches of breakings, and of the cluster sizes of broken fibers. Finally, we analyze the moments of the cluster size distributions to accurately determine the value at which the crossover is observed.Comment: 8 pages, 8 figures. Two columns revtex format. Final version to be published in Phys. Rev.

ANALYSIS OF HOT CARRIER DEGRADATION IN AC STRESSED N-CHANNEL MOS TRANSISTORS USING THE CHARGE PUMPING TECHNIQUE

La dégradation par porteurs chauds (hot carriers) de transistors nMOS, induite lors de l'application de tensions alternatives (AC-stress) a été évaluée en utilisant la technique Charge Pumping et les résultats ont été comparés à ceux d'une contrainte sous tension continue. En outre d'une composante de dégradation uniquement dépendante du temps de vieillissement, une composante additionnelle a été observé qui est proportionnelle au nombre d'impulsions appliquées (fréquence * temps). La dégradation s'avère fortement dépendante de la forme de l'impulsion à la grille. En effet, nos expériences prouvent d'une part que le temps de descente de l'impulsion de grille est beaucoup plus important que le temps de montée, et d'autre part que la largeur de l'impulsion de grille détermine le degré de compensation de la charge positive piégé durant la période de tension basse à la grille, par des électrons injectés durant la période de tension haute.Hot carrier degradation induced during AC-stressing of NMOS transistors is evaluated using the charge pumping technique and the results are compared with those from DC-stress. Besides a degradation component that is only dependent on stress time, an additional component is observed that is proportional to the number of applied pulses (frequency * time). A strong dependency of the degradation on the shape of the gate pulse is demonstrated. The falling edge of the gate pulse is shown to be much more important than the rising edge and the width of the gate pulse determines the amount of compensation of the trapped positive charge by injected electrons

Switching quality of thin-film PZT ferroelectric capacitors

The switching quality of PZT thin-film ferroelectric capacitors was studied, using hysteresis and pulse switching measurements. The ferroelectric properties of epitaxial Pt/PZT/LSCO/MgO capacitors are strongly affected by the LSCO material. A strong deviation between hysteresis and pulse measurements has been observed for one type of LSCO, corresponding to a strong relaxation of (oxygen-vacancy) space charge polarization. On the other hand, polycrystalline Pt/PZT/Pt show very rectangular hysteresis loops with high Pr and pulse measurements reveal high speed switching and absence of rapid depolarization effects. These results prove the very high switching quality of Pt/PZT/Pt capacitors, required for their application as non-volatile memory elements