Author: CARLOS ZUÑIGA ISLAS

Study of fluorescence of yttrium doped zinc sulfide nanoparticles

VALENTIN LOPEZ GAYOU CARLOS ZUÑIGA ISLAS (2010)

Doped ZnS nanocrystals have attracted attention since 1994. Previous results suggest that doped semiconductor nanocrystals form a new class of luminescent materials, which have a wide range of applications in displays, lighting, sensors and lasers. In this work we synthesized Y3+ doped ZnS nanoparticles by a chemical precipitation method. The reaction was performed with ZnSO4, Na2S, phosphates and Yttrium acetate in aqueous solution. Fluorescence (FL) studies of these nanoparticles have been carried out. FL analysis reveals that the incorporation of Yttrium and phosphates to colloidal solution of ZnS nanoparticles enhances the FL signal by 6-7 times of magnitude compared with uncapped ZnS nanoparticles.

Article

Nanoparticles Zinc sulfide Yttrium Fluorescence CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

Arreglo de microelectrodos planares con procesos CMOS estándar (Semiconductor Complementario Metal-Oxido)

BLANCA SUSANA SOTO CRUZ CARLOS ZUÑIGA ISLAS (2011)

Se presenta el diseño e integración en el mismo substrato, de un arreglo de microelectrodos planares y el circuito de lectura implementado en un proceso comercial estándar CMOS (Semiconductor Complementario Metal-Oxido), de 0.6 μm. El diseño incluye el blindaje alrededor del arreglo de microelectrodos y el control del filtro pasabanda a través de la compuerta de transmisión CMOS operando en la región de subumbral. Esto se logra variando el voltaje de compuerta en un rango de 400 a 800 mV para un rango de frecuencia de corte bajo de 1 hasta 1 KHz. El funcionamiento del circuito con polarización de ± 1.5 V dio una ganancia de 40 dB, PSRR (razón de rechazo de la potencia aplicada) de 44 dB y CMRR (razón de rechazo de señales comunes) de 87 dB en un área 0.014 mm2 haciéndolo un buen prospecto para la aplicación biológica.

The design and the on-chip integration of planar microelectronic array and the read-out circuit implemented by 0.6 μm CMOS process (Complementary Metal–Oxide–Semiconductor), is presented. The design includes a shielding ring around the microelectrode array and a control for a tunable low pass filter, which are made with a CMOS transmission gate operating in subthreshold region. This is achieved by varying the gate voltage in a range from 400 to 800 mV for a frequency range of 1 to 1KHz. The performance of the circuit with a voltage supply ± 1.5 V was 40dB gain, 44 dB PSRR (power supply rejection ratio) and 87 dB CMRR (common-mode rejection ratio), in an area of 0.014mm2, showing that the system is a good alternative for biological applications.

Article

CMOS Microelectrodo Compuerta de transmisión Bipotenciales Filtro pasabanda Microelectrode Transmission gate Biopotentials Passband filter CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

Digital output silicon optical sensors

OLEKSANDR MALIK FRANCISCO JAVIER DE LA HIDALGA WADE CARLOS ZUÑIGA ISLAS (2008)

For the first time, a detailed description of lowcost newintelligent (or smart) two-terminal optoelectronic devices without any on-chip circuitry for signal processing is presented. The design of the devices is based on the intelligent integration of micro-sized diodes and metal-oxide-semiconductor (MOS) capacitors. By combining physical processes and a functional voltage bias, such optical sensors transform the received analog input nonmodulated optical signal directly into a pulse-width modulated electrical signal; the duty of the signal depends on the irradiation level, and the whole process is conducted without any integrated or external analog-to-digital converter. When the optical sensors operate under a pulsed irradiation synchronized with the functional voltage bias, unconventional logic properties are obtained that can be used to identify the emission from two equal LEDs.

Article

Silicon Optical sensor Intelligent sensor Digital output CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Pulse characteristics of silicon double barrier optical sensors with signal amplification

OLEKSANDR MALIK FRANCISCO JAVIER DE LA HIDALGA WADE CARLOS ZUÑIGA ISLAS (2008)

The pulse characteristics of optical sensors with double potential barriers formed on the opposite sides of a high-resistivity (v) silicon substrate have been studied. The first barrier is formed by multiple micro-sized Ti–vSi contact barriers surrounded by Ti–SiO2–vSi MOS structures. The second one is the v–n+ potential barrier formed at the bottom of the wafer. The structure presents signal amplification for both polarities of the applied voltage. Under negative bias applied to the semi-transparent Ti-electrode, the reason of the current gain is the change in the transport mechanism of carriers through the potential barrier of the Schottky barrier along its perimeter, which is due to the strong electric field originated by the photogenerated minority carriers forming an inversion layer at the silicon-oxide interface. Under positive bias, the current gain is due to the operation of the v–n+ potential barrier, which was studied earlier, and in this work it is used for comparison purposes.

Article

Optical sensors Silicon Signal amplification Double barrier structures CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Optimization of the contact resistance in the interface structure of n-type Al/a-SiC:H by thermal annealing for optoelectronics applications

ROBERTO AMBROSIO ALFONSO TORRES JACOME CARLOS ZUÑIGA ISLAS MARIO MORENO MORENO JOSE MIRELES JR. GARCIA (2010)

The presented work meets the requirements for integration of amorphous silicon carbon films with silicon technology in order to obtain a complete optoelectronic system such as light emitting diodes and its electronic readout circuits. The key enabler for this integration scheme is the low temperature of deposition of a‐SiC:H films and an ohmic behavior in the interface metal/a‐SiC:H. In this work, the optimization of the interface Al/a‐SiC:H films are performed by means of thermal annealing timing. The a‐SiC:H films were deposited by enhanced chemical vapor deposition from CH4/SiH4 and C2H2/SiH4 mixtures. The structural and optical properties of the deposited films are presented. An implantation phosphorous dose was used for doping before fabrication of patterned aluminum contacts. The implanted films were electrically characterized by the transfer length method (TLM) measuring a sheet resistance value as low as 171 MΩ/square. The Schottky behavior was improved to ohmic behavior after several hours in thermal annealing treatments at 350 °C, which allows to obtain a reasonable contact resistance values in the range from 8.6 to 26.8 kΩ.

Article

Annealing Contact resistance Electrical properties Interface formation LEDs PECVD SiC Structure CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

UV-sensitive optical sensors based on ITO-gallium phosphide heterojunctions

OLEKSANDR MALIK FRANCISCO JAVIER DE LA HIDALGA WADE CARLOS ZUÑIGA ISLAS JESUS HUMBERTO ABUNDIS PATIÑO (2010)

Design and characteristics of wide-band UV sensors based on ITO/GaP heterostructures are discussed. Such sensors have perfect electrical parameters and high UV-visible sensitivity in comparison with surface-barrier structures using a semitransparent thin metal film as an electrode. Many applications require UV sensors with an effective rejection of visible radiation and a wide temperature operating interval. For this aim, the theoretical modelling of extreme selective optical sensors with a double Ag/ITO thin film on the GaP surface, in which the thin silver film serves as a narrow bandpass filter at 320 nm, has been conducted. With this modelling the optimal thickness combination for the silver and ITO films was found for the maximum rejection of the sensitivity to visible radiation.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

IR sensors based on silicon–germanium–boron alloys deposited by plasma: Fabrication and characterization

ANDREY KOSAREV MARIO MORENO MORENO ALFONSO TORRES JACOME CARLOS ZUÑIGA ISLAS (2008)

We report the study of a fabrication process and characterization of a thermal IR sensor based on silicon–germanium–boron alloys (a-SixGeyBz:H) deposited by plasma at low temperature. The sensor is an un-cooled micro-bolometer fabricated with surface micromachining techniques and is fully compatible with the CMOS technology. The temperature dependence of conductivity δ(T) was measured in the sensor in order to calculate the activation energy, Ea, the temperature coefficient of resistance, TCR and the room temperature conductivity, δRT. Current–voltage characteristics, I(U), in darkness and under IR radiation were measured in the device in order to calculate its current responsivity, RI. Spectral noise density was measured and the micro-bolometer detectivity, D* was calculated. The thermal time constant of the micro-bolometer was also measured.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Efficient ITO–Si solar cells and power modules fabricated with a low temperature technology: Results and perspectives

OLEKSANDR MALIK FRANCISCO JAVIER DE LA HIDALGA WADE CARLOS ZUÑIGA ISLAS GUILLERMO RUIZ TABOADA (2008)

ITO–SiOx–nSi semiconductor–insulator–semiconductor (SIS) structures have been produced with a simple spraying technique. It is shown that the structures obtained in such a way may be considered as an induced p–n diode, in which the polycrystalline tin–doped indium oxide (ITO) layer spray deposited on the preliminary treated silicon surface leads to an inversion p-layer at the interface. Solar cells with an active area of 1–4 cm2 have been fabricated based on ITO–SiOx–nSi structures and studied. Under AM0 illumination conditions, the efficiency is nearly 11%, whereas it exceeds 12% for AM1.5 illumination conditions. The theoretical analysis provided in this work shows a good agreement with experimental results and allows for predicting the efficiency of the cells depending on the silicon electro-physical properties.

Article

Silicon Solar cells Photovoltaics Indium tin oxide and other transparent conductors CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Electrical characterization of a-C:H as a dielectric material in metal/insulator/metal structures

CARLOS ZUÑIGA ISLAS ANDREY KOSAREV ALFONSO TORRES JACOME PEDRO ROSALES QUINTERO WILFRIDO CALLEJA ARRIAGA FRANCISCO JAVIER DE LA HIDALGA WADE OLEKSANDR MALIK (2010)

The fabrication and electrical characterization of Metal- Insulator-Metal (MIM) structures, using a-C:H films as the insulating material, are presented in this work. These PECVD carbon films show a very low dielectric constant and a very high resistivity. The current conduction mechanisms were analyzed before and after the post deposition annealing in pure argon ambient at 400°C. For as-deposited films, the experimental J-U curves showed that under low biasing regime (|U| < 8 V) the space charge limited current conduction is the main transport mechanism, whereas under higher biasing regime (|U| > 8 V)) the current transport is dominated by the Schottky mechanism. For annealed structures, under low and high biasing the ohmic and Schottky mechanisms were identified as the main processes for the electrical transport. Finally, we found that both parameters, the dielectric constant and resistivity, decrease slightly after the thermal annealing.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

Impact of the base doping concentration on the transport mechanisms in n-type a-SiGe:H/p-type c-Silicon Heterojunctions

Pedro Rosales Quintero MARIO MORENO MORENO ALFONSO TORRES JACOME FRANCISCO JAVIER DE LA HIDALGA WADE Joel Molina Reyes Wilfrido Calleja Arriaga CARLOS ZUÑIGA ISLAS (2011)

The charge transport mechanisms occurring in n-type a-SiGe:H on p-type c-Si heterojunctions were determined by analyzing the temperature dependence of the current-voltage characteristics in structures with four different peak base doping concentrations (NB = 1x10^15, 7x10^16, 7x10^17 and 5x10^18 cm-3). From the experimental results, we observed that at low forward bias (V< 0.45V) the current is determined by electron diffusion from the n-type amorphous film to the p-type c-Si for the heterojunction with NB = 1x10^15cm-3, whereas the Multi- Tunneling Capture Emission (MTCE) was identified as the main transport mechanism for the other base doping concentrations. On the other hand, at high forward bias (V> 0.45V), the space charge limited current effect became the dominant transport mechanism for all the measured devices. Under reverse bias the transport mechanisms depends on the peak base doping, going from carrier generation inside the space charge region for the lowest doping, to hopping and thermionic field emission as the base doping concentration is increased.

Heterouniones de a-SiGe:H tipo-n sobre silicio cristalino tipo-p con cuatro diferentes concentraciones pico en la base (1x10^15, 7x10^16, 7x10^17 y 5x10^18 cm-3) fueron fabricadas y caracterizadas. Los mecanismos de transporte se determinaron por medio de sus curvas características de corriente vs voltaje en función de la temperatura. El análisis de los resultados muestra que a bajos voltajes de polarización directa (V< 0.45V) en la heterounión con la menor concentración pico la corriente es determinada por la difusión de electrones del a-SiGe:H tipo-n hacia el silicio cristalino tipo-p. Mientras que el multituneleo captura-emisión (MTCE) es el principal mecanismo de transporte en las otras heterouniones. A altos voltajes de polarización directa (V> 0.45V) el efecto de corriente limitada por carga espacial (SCLC) es el mecanismo de transporte dominante en todos los dispositivos caracterizados. El incremento en la concentración de dopantes en la base, además, causa un aumento en la corriente inversa.

Article

Amorphous semiconductors Heterojunction diodes Transport mechanisms Base doping concentration Semiconductores amorfos Heterouniones Mecanismos de transporte Concentración de dopantes en la base CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA