1,721,039 research outputs found
Porous Silicon Microcavities as Optical and Electrical Chemical Sensors
No full textThe optical and electrical properties of porous silicon microcavities are strongly dependent on the environment. For highly luminescent samples both the luminescence intensity and the peak position are affected by organic substances, which also strongly modify the electrical conductivity, giving the possibility to obtain a multi-parametric optical/electrical sensor. The peak position depends on the refractive index of the organic compound, whereas the luminescence intensity depends on its low frequency dielectric constant. Electrical properties depend on the dipole moment of the molecules. This allows discriminating between different organic substances
CMOS fabrication of a light emitting diode based on silicon/porous silicon heterojunction
No full textThe fabrication in a standard CMO line of a light emitting diode (LED) based on silicon/porous silicon heterojunction is discussed. To fabricate the LED in a CMOS line, the porous silicon formation must be performed either as the last or as an intermediate step. The former option requires a masking layer to protect the metallization level of the CMOS devices from the electrochemical solution for the porous silicon formation, whereas the latter forces an interruption in the process. Experimental test on several materials, routinely used in CMOS processes, show that no standard mask is suitable to fully protect the CMOS from the electrochemical etch. Hence porous silicon formation should be performed as an intermediate ste
Vapor control of resonant Zener tunneling of light in a photonic crystal
No full textWe show a vapor controlled one-dimensional photonic crystal built with a silicon-based dielectric mesoporous material, in which the refractive index can be continuously tuned by flowing organic vapors through the pores. Exposure of the crystal to vapors induces an inhomogeneous change in the refractive index through the depth and results in a tilted photonic band structure. We drive the photonic crystal to the optical Zener breakdown condition, introducing an enhanced transmission channel through the crystal.
This phenomenon closely resembles the electronic Zener breakdown in a reverse-biased p–n junction. The effect is reversible and opens new perspectives for physics in photonic crystals and novel device concepts based on sensing, switching and processing of light
CMOS compatible Si/SiO2 multilayers for Light Emitting Diodes
No full textWe report photoluminescence and electroluminescence at room temperature in diodes based on Si/SiO2 multilayers. The multilayers are fabricated by alternating Si and SiO2 layers, whose thickness is, respectively, 3.5 and 5 nanometers. In photoluminescence, a single band is observed, centered at 800 nm, which is due to electron-hole pair recombination under quantuum confinement. on the other hand, in electroluminescence, two bands are reported. The first band is in the infrared spectrum, and is blackbody radiation. The second band is visible, and is originated by relaxation of a single type of electrical carrier (electrons), as suggested by a fast decay time (less than 0.1 s). Possible mechanisms can be hot-electron relaxation or coupling with surface plasmon-polariton
Visible light emission from a new material system: Si/SiO2 superlattices in optical microcavities
No full textIn order to add optical functionalities to silicon based microelectronics, we decided to develop Si/SiO2 superlattices where quantum confinement effects should drive Si to become a good emitter. A further improvement is possible when one couples the beneficial effects of low dimensional electronic systems (as in Si superlattices) with the enhancement of the spontaneous emission rate that occurs in an optical microcavity. Not to lose the fundamental goal to add optical functionality to electronic circuits we have performed the growth of this material in an industrial environment by using standard CMOS equipments. In this paper we will present the status of our researc
Porous Silicon
No full textThis article deals with generalities and definitions of porous silicon (PSi): fabrication techniques, structural properties, chemical properties, electronic properties, electrical properties, optical properties, and actual or potential applications of PSi. Optical properties include light transport, photoluminescence, and electroluminescenc
Light Emitting diodes based on anodically oxidized silicon/porous silicon heterojunction
No full textAn improved test device, based on the light emitting device (LED) presented in the following article (L. Pavesi, R. Guardini, P. Bellutti, Thin Solid Films 297 (1997) 272) is reported. The whole processing of the diode is CMOS compatible and the porous Si (PS) formation is at the end of the run. The idea of the LED is to exploit the doping selectivity of the silicon anodization by forming n+ -type doped crystalline Si stripes floating over the porous silicon layer. Electrical injectionis through the n+ stripes into the PS, i.e. through a SI/PS heterojunction. Here, the electrical and optical properties of the electochemically oxidized LED are characterized. Anodic oxidation improves the LED performance both in terms of stability (more than 8 days under CW excitation) and efficiency (a factor 3 or higher with respect to the as-grown LED
Monitoring penetration of ethanol in a porous silicon microcavity by photoluminescence interferometry
No full textA photoluminescent porous silicon microcavity is exposed to saturated vapor of ethanol. The ethanol substitutes the air inside the pores giving rise to a progressive monotonic redshift of the interference pattern of the photoluminescence spectrum. On the other hand, the photoluminescence intensity of the cavity peak oscillates in time. Both effects can be explained in terms of a very simple model based on the progressive change of the effective refractive index of single layers of the cavity. The change is due to the difference between the index of refraction of air and ethanol. The result suggests that a porous silicon microcavity can be a tool to study the dynamics of gas penetration into porous silicon since it allows a monitoring of the depth reached by the ethanol at any given time
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