Planar Gunn diodes on In 0.53 Ga 0.47 As with lengths between 2 and 5 µm have been fabricated and characterized in a temperature range of 10 to 300 K. Two different oscillation regimes are observed depending on temperature. At the higher values, the frequency of the oscillations decreases as the bias increases, as expected for a well-established transit-time domain mode. But below approximately 75 K, the behavior is the opposite, the frequency of the Gunn oscillations increases with the bias. This fact, together with a much lower amplitude of the oscillations, indicate the possible switch to a different oscillation mode in which the domains are not able to attain their complete maturation before reaching the anode.

Second harmonic light generation (SHG) was observed from as-deposited silica glass thin films suitable for waveguiding, without the need for an inversion symmetrybreaking poling treatment. Thin film stacks of up to 16 layers of alternating 2% phosphorusdoped and undoped silica glass on silica substrates were prepared and probed with a pulsed Nd:YAG laser at 1064 nm. We observed that even though these structures were not poled, they possess a net second order non-linearity with a value of the order of 0.03 pm/V. The SHG increased with the number of layers (total thicknesses between 4 and 9.6 µm have been tested) and also depended on the thickness ratio between the doped and undoped layers. Annealing at 800°C for 4 hours removed the nonlinearity completely.

Cuando Albert Einstein concibió la energía láser en el año 1919, no podía imaginar los múltiples usos que iba a tener en el futuro. Hoy el láser sirve a la industria electroquímica, alas comunicaciones y, no de menos, a la de cirugía, habiendo hecho posible una verdadera revolución dentro de este campo. La palabra es una abreviatura en inglés, ligh amplification by stimulated emision of radiation, es decir, luz amplificada por la emisión estimulada de la radiación. Lo que determina laspropiedades del rayo láser y determina su poder enérgico y amplitud de onda, es un cristal, un líquido o un gas que al estar contenido en una cavidad óptica su moléculas son estimuladaspor una fuente de electricidad y luego al regresar a su estado basal emite unos fotones, partículas de luz, llamada rayo láser.Este rayo difiere de la luz que todos conocemos; por ejemplo, la emitida por un bombillo es desordenada, en direcciones y colores múltiples; en cambio el láser posee propiedadesespecíficas que son la coherencia, organización y monocromicidad (un solo color). Es el conocimiento de estas características y su interacción con los tejidos lo que ha permitidouna aplicación orientada y precisa como herramientamédica.

The responsivity of AlGaN/GaN high-electron mobility transistors (HEMTs) when operating as zero-bias RF detectors in the subthreshold regime exhibits different behaviors depending on the operating temperature and gate length of the transistors. We have characterized in temperature (8–400 K) the detection performance of HEMTs with different gate lengths (75–250 nm). The detection results at 1 GHz can be reproduced by a quasi-static model, which allows us to interpret them by inspection of the output ID − VDS curves of the transistors. We explain the different behaviors observed in terms of the presence or absence of a shift in the zero-current operating point originating from the existence of the gate-leakage current jointly with temperature effects related to the ionization of bulk traps.

No abstract