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Metal contacts on GaSb substrates and GaInAsSb epilayers for infrared detector applications

JOSE LUIS HERRERA CELIS (2012)

Any electronic device requires ohmic contacts for interconnection with the outside. In this case, a manufacturing process of ohmic contacts on GaSb substrates and GaInAsSb epilayers was tested as part of the manufacture of an infrared detector for monitoring environmental aromatic pollutants. The process includes seven steps: cleaning, surface passivation, thermal annealing premetallization, photolithography, metallization, lift-off and thermal annealing after metallization. In order to validate the process and to know the effects of each step, a series of tests were carried out using GaSb substrates. Those tests show mainly the effects of the passivation and the thermal annealing on contact parameters. In GaInAsSb epilayers, the cleaning procedure and the metal layers deposited were changed taking into account the previous results and the composition of the epilayers.

Through the complete process and depositing Pd/In/Pd/Au-Ge/Pd/Au on GaSb, ohmic contacts with a linear current-voltage characteristic have been obtained. Moreover, Schottky barriers have been the result of applying the process on GaInAsSb epilayers. Thus, taking into account the effects of the carrier concentration in the height and width of the barrier, tests on GaInAsSb epilayers doped in the range of 5×1015−8×1017 𝑐𝑚−3 have been carried out. I-V measurements show the domain of the field emission mechanism on the thermionic emission mechanism as the doping density increases.

Todo dispositivo electrónico requiere contactos óhmicos para interconectarse con el exterior. En este caso, un proceso de fabricación de contactos óhmicos (sobre sustratos de GaSb y películas cuaternarias de GaInAsSb) ha sido probado como parte de la fabricación de un detector infrarrojo para el monitoreo de contaminantes ambientales de tipo aromático. El proceso contempla siete pasos: limpieza, pasivación de la superficie, recocido térmico antes de la metalización, fotolitografía, metalización, lift-off y recocido térmico después de la metalización. Para validar el proceso y conocer los efectos de cada paso se llevaron a cabo una serie de pruebas empleando sustratos de GaSb. Estas pruebas revelan principalmente los efectos de la pasivación y los recocidos térmicos sobre los parámetros de contacto. En las películas de GaInAsSb, el procedimiento de limpieza y las capas de los metales depositados fue modificado teniendo en cuenta los resultados preliminares y su composición.

Con el proceso completo y depositando Pd/In/Pd/Au-Ge/Pd/Au sobre GaSb, se obtuvieron contactos óhmicos con una característica corriente-voltaje lineal. Por otra parte, barreras Schottky han sido el resultado de aplicar el proceso a muestras de GaInAsSb. Por ende, teniendo en cuenta los efectos de la concentración de portadores en el alto y ancho de la barrera, se llevaron a cabo pruebas sobre películas de GaInAsSb dopadas en el rango de 5.0×1015−8.0×1017 𝑐𝑚−3. Las mediciones I-V revelan el dominio del mecanismo de conducción de efecto de campo sobre el mecanismo de conducción de emisión termoiónico a medida que la concentración de portadores aumenta.

Master thesis

Contact resistance Semiconductor epitaxial layers Rapid thermal processing Passivation CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Estudio fotocatalítico de Ti02 modificado con Etilendiamina, acoplado aBivo4 e Invo4 en reacciones de oxidación y reducción de compuestos orgánicos inducidas por luz visible

SANDRA CIPAGAUTA DIAZ (2017)

El presente trabajo de investigación comprende la elaboración de fotocatalizadores de dióxido de titanio modificado con nitrógeno (TiEN); TiEN acoplado a BiVO4 (TNB) y TiEN acoplado a InVO4 (TNI) haciendo uso del método hidrotérmico. La serie de materiales TNB y TNI se sintetizaron al 1, 3 y 5 % en peso de BiVO4 e InVO4, respectivamente. En una primera etapa los materiales fueron ampliamente caracterizados por diversas técnicas estructurales, morfológicas y ópticas, con el objetivo de estudiar las propiedades de los sólidos y su correlación con la actividad fotocatalítica. La segunda etapa comprendió la evaluación de la actividad fotocatalítica en luz visible en oxidación y reducción de moléculas orgánicas contaminantes. La serie de catalizadores TNB fue probada en la eliminación de Ofloxacina (OFX) y Naproxeno sódico (NPX). Así mismo, esta última molécula, fue empleada, para evaluar la degradación de los materiales TiEN. El sólido TiEN*5 presentó mejor actividad fotocatalítica que Degussa P25 y TiO2 sol gel bajo radiación de luz visible debido principalmente a una óptima cantidad de nitrógeno sustituido en la red. La serie de materiales TNB presentaron mejores propiedades de absorción en el intervalo de luz visible debido principalmente a un efecto sinérgico del material TiEN y BiVO4. El material TNB-1 presentó una mayor eficiencia en la mineralización de los contaminantes OFX y NPX comparado con el material TiEN. Los estudios de reciclado demuestran la estabilidad y eficiencia del material TNB-1 en la fotodegradación de contaminantes orgánicos. El acoplamiento de InVO4 en TiEN permitió la fabricación de materiales TNI con mejores propiedades fotocatalíticas, debido a una mejor respuesta a la luz visible. Los catalizadores TNI se evaluaron en la reducción fotocatalítica de la molécula 4-Nitrofenol (NF) a 4- Aminofenol (4-AF), en 9 Sandra Cipagauta Díaz presencia de sulfito sódico como agente de sacrificio, utilizando luz visible como fuente de radiación. Esta mejora en las propiedades está determinada por los efectos sinérgicos de las características morfológica, químicas y ópticas de los materiales TiEN e InVO4. El material TNI-3 fue el que presento mayor actividad. Finalmente, las pruebas de reciclado mostraron que después de 3 ciclos, el material TNI-3 mantiene su fotoactividad en el proceso de reducción de 4-NP. Los resultados obtenidos, mostraron que el dopaje de TiO2 con Nitrógeno y su acoplamiento con BiVO4 e InVO4 contribuyen al conocimiento de investigaciones realizadas para el mejoramiento del TiO2 para aplicaciones fotocatalíticas en la degradación y reducción de contaminantes orgánicos en luz visible.

Doctoral thesis

Compuestos orgánicos Ecología marina Dióxido de titanio Semiconductor BIOLOGÍA Y QUÍMICA

A reconfigurable multimode interference splitter for sensing applications

DANIEL ALBERTO MAY ARRIOJA JOSE JAVIER SANCHEZ MONDRAGON ROMEO DE JESUS SELVAS AGUILAR ISMAEL TORRES GOMEZ (2007)

A reconfigurable multimode interference (MMI) coupler is demonstrated.

The device operates by modifying the phase of the multiple images that are

formed around the midpoint of the MMI section. This modifies the

properties of the following set of images, and light can be directed to a

specific output waveguide, which is therefore ideal to develop a

reconfigurable MMI coupler. In our device the phase change is achieved by

current injection, and therefore minimizing current spreading is crucial for

optimal operation. A zinc in-diffusion process has been implemented to

selectively define p–n regions and effectively regulate current spreading by

controlling the depth of the zinc doping. Using this process, a

reconfigurable 3 dB MMI coupler has been fabricated. Our experimental

results revealed that the device can be easily set to a perfect 3 dB splitter

using only 0.7 mA of current injection. In addition, the device can be

adjusted all the way from a 90:10 to a 30:70 splitting ratio. The results are

very encouraging since, to our knowledge, this degree of tuning of the

optical power has never been experimentally demonstrated in MMI devices.

Furthermore, this concept can easily be applied to a wide variety of

semiconductor photonic switches that operate on MMI effects.

Article

Sensors MMI Multimode interference Tunable coupler Integrated sensor Integrated optics Semiconductor Quantum-well devices CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA

Diseño Molecular Asistido por Computadora: Aplicación al Diseño de Cúmulos Mixtos de Silicio-Germanio

ZEFERINO GOMEZ SANDOVAL JUVENCIO ROBLES GARCIA (2012)

In this work, electronic structure calculations have been performed to obtain the minimum potential energy structures of pure and mixed silicon-germanium clusters (cluster size within 2-6 atoms). Furthermore the electronic structure and various physical and chemical properties are studied. Properties useful for electronics applications, like heat of formation, ionization potentials, electron affinity, absolute hardness, electronegativity, hybridization, vibrational frequencies, fragmentation and bond dissociation energy of these silicon-germanium clusters are discussed. Thereafter, the evolution of the mixed clusters geometries with increasing germanium composition is also discussed. The most stable mixed silicon-germanium clusters are predicted for four and six atoms components and some with nuclearity equal to five such as SiGe4, Si2Ge3, and Si3Ge2.

Article

INGENIERÍA Y TECNOLOGÍA Silicon Germanium Cluster Semiconductor Computational chemistry

The deposition and control of self assembled silicon nano islands on crystalline silicon

ZHENRUI YU MARIANO ACEVES MIJARES (2008)

The formation of nano sized Si structures during the annealing of silicon rich oxide (SRO) films was investigated. These films were synthesized by low pressure chemical vapor deposition (LPCVD) and used as precursors, a post-deposition thermal annealing leads to the formation of Si nano crystals in the SiO2 matrix and Si nano islands (Si nI) at c-Si/SRO interface. The influences of the excess Si concentration, the incorporation of N in the SRO precursors, and the presence of a Si concentration gradient on the Si nI formation were studied. Additionally the influence of pre-deposition substrate surface treatments on the island formation was investigated. Therefore, the substrate surface was mechanical scratched, producing high density of net-like scratches on the surface. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize the synthesized nano islands. Results show that above mentioned parameters have significant influences on the Si nIs. High density nanosized Si islands can epitaxially grow from the c-Si substrate. The reported method is very simple and completely compatible with Si integrated circuit technology.

Article

Si nano islands Self assembly Epitaxial growth Silicon-rich oxide Photoluminescence CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Enlarged sheet of ZnS(en)0.5 hybrid semiconductors with photocatalytic activity

Agileo Hernández Gordillo VICENTE RODRIGUEZ GONZALEZ ETEL MAYA FLORES (2015)

"Sheets of ZnS(en)0.5 hybrid semiconductors were prepared by the precipitation method in an ethylenediamine–water solution and it was enlarged by varying the aging at a long period time. The characterization of the hybrid material was carried out by different techniques such as FTIR, DRS-UV–vis spectroscopies and scanning electron microscopy (SEM). The number of intercalated ZnS layers in a ZnS(en)0.5 hybrid semiconductor was proposed to be determined by XRD. The photocatalytic activity of the enlarged sheet of ZnS(en)0.5 hybrid was investigated in the photoreduction of 4-nitrophenol to 4-aminophenol in the presence of hydrazine under UV light irradiation. The intrinsic photocatalytic activity of the ZnS(en)0.5 semiconductor sheets was associated with the number of intercalated ZnS layers, and possible mechanism of the electron transfer process was discussed."

Article

Enlarged sheets ZnS(en)0.5 hybrid Intercalated layers 4-nitrophenol photoreduction CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA FÍSICA

Antireflective embedded MSM photodetector: An architectural optimization

GUILLERMO FERNANDO CAMACHO GONZALEZ (2015)

Photodetectors are essential elements in optoelectronics because they are the

communication via between light and electronics. There are several kinds of photodetectors but

nowadays the most used are semiconductor photodetectors due to its versatility when detecting

light of specific wavelengths efficiently and with fast response velocity.

Most semiconductor photodetectors are fabricated with striped interdigitated electrodes

over a semiconductor substrate (MSM photodetectors), in order that we have periodicity between

metallic electrodes and semiconductor regions on top photodetector surface. These kind of

photodetectors are widely used in communications due to its faster response compared to other

photodetector structures1’2’3 and they are a very good for UV detection4’5. Light is detected when it

reaches the semiconductor region by creating charge carriers (holes and electrons) that are then

transported to the electrodes due to an applied voltage difference6. Interdigitated electrodes are

used to increase the active region area (semiconductor) while optimizing the electric fields between

electrodes for carrier collection meaning high velocity response and sensitivity, but unfortunately it

also provokes that certain amount of light get back reflected by the electrodes surfaces. Many

methods to compensate this loss have been proposed, some examples are: using metallic gratings

Master thesis

Photodetectors Antireflection layers Metallic electrodes CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA

Effect of Boriding on the Mechanical Properties of AISI 1045 Steel

GERMAN ANIBAL RODRIGUEZ CASTRO IVAN ENRIQUE CAMPOS SILVA José Francisco Martínez Trinidad Ulises Figueroa López LUIS DANTE MELENDEZ MORALES JESUS VARGAS HERNANDEZ (2009)

Efecto en las propiedades mecánicas de un acero borurado 1045.

Some mechanical properties of AISI 1045 borided steels were estimated in the present work. The boriding process was carried out by the powder pack method at 950°C with 8 h of treatment. The fatigue strength on borided notched specimens was evaluated with rotating bending tests (R=1) considering a stress concentration factor (Kt) of 2.53. Likewise, the presence of residual stresses in boride layers was established by the XRD technique. The Daimler-Benz Rockwell C test was used, also, to estimate the strength adhesion of the coated system. The results show a decrease in the fatigue strength of AISI borided steels due to the presence of high porosity in the layers. Finally, the Rockwell-C adhesion test showed no coating failure for the boride layer.

Article

Boriding Boride Layers Fatigue strength Adhesion Residual stresses Porosity INGENIERÍA Y TECNOLOGÍA

Nanopartículas de HfO2 embebidas en una matriz de óxido spin-on-glass como capa de atrapamiento de carga para dispositivos de memoria

RAFAEL ORTEGA HERNANDEZ (2012)

The technological progress and the scaling down of electronic devices have

carried out to new research in nonvolatile memory industry. The typical

silicon-oxide-nitride-oxide-silicon (SONOS) charge trapping-based nonvolatile

memories have been widely studied in past years. The main problem of

SONOS devices is the high leakage current due to scaling down of ONO

layers. There are a wide variety of films with higher dielectric constant values

(κ) other than SiO2 which seems to solve the leakage current problem. At this

time, interest is centered on films such as HfO2 with κ value of 25 which

appears to be a promising candidate to replace Si3N4 films as the charge

trapping layer of SONOS-type memory devices. These high-κ materials lead

to a new type of memory structure Metal/Oxide/High-κ oxide/Oxide/Silicon

(MOHOS) memory.

In this thesis we present the use of HfO2 nanoparticles (np-HfO2) embedded

in a spin-on glass oxide matrix as an active charge trapping layer for

MOHOS-type memory structures. The deposition of charge-trapping layer is

performed by the sol-gel technique and it is characterized at different np-HfO2

concentrations. Fourier Transform Infrared Spectroscopy (FTIR) in

absorbance mode is used to observe the presence of chemical bonding

presented in the high-κ layer. Also, different annealing temperatures are

experimented for final curing of this film. The top oxide of the structure is also

deposited by the sol-gel method. For this layer, the same spin-on glass that

was used for embedding np-HfO2 is used. For these reasons, the MOHOStype

structure is obtained by a very simple and low-cost deposition method.

Finally, figures of merit like programming (writing/erasing) times and retention

time are presented and correlated to obtain the general performance of the

MOHOS-type memory devices.

El progreso tecnológico y el escalamiento de los dispositivos electrónicos han

llevado a la investigación en nuevas áreas en la industria de dispositivos de

memorias no volátiles. La memoria no volátil de atrapamiento de carga silicio-xido-nitruro-óxido-silicio (SONOS) ha sido ampliamente investigada en años

anteriores. Sin embargo, el principal problema de los dispositivos de memoria

SONOS son las corrientes de fuga debido a la reducción en el espesor de la

estructura ONO. Existe una amplia variedad de materiales con una constante

dieléctrica (κ) mayor que la del dióxido de silicio (SiO2) que pueden resolver

el problema de corrientes de fuga. Por el momento, nuestro interés se centra

en el óxido de hafnio (HfO2), con un valor de constante dieléctrica κ≈25, el

cual parece ser un posible material para reemplazar la capa de nitruro de

silicio (Si3N4) como la capa de atrapamiento de carga en dispositivos de

memoria SONOS. Estos materiales de alta constante dieléctrica dan lugar a

un nuevo tipo de dispositivos de memoria Metal/Oxido/Oxido de alta

κ/Oxido/Silicio (MOHOS).

En esta tesis, se presenta el uso de nanopartículas de HfO2 (np-HfO2)

embebidas en óxido spin-on glass como carga de atrapamiento de carga en

estructuras de memoria tipo MOHOS. El depósito de la capa de atrapamiento

de carga se realiza mediante la técnica sol-gel y se experimenta con

diferentes concentraciones de np-HfO2. El estudio de composición química

de esta capa se lleva a cabo a través de Espectroscopia de Transformada de

Fourier en Infrarrojo (FTIR). También, se experimenta con diferentes

temperaturas de curado de la capa de alta constante dieléctrica. El óxido de

bloqueo se deposita por el método de sol-gel. De esta forma, la obtención de

la estructura tipo MOHOS se lleva a cabo de una manera sencilla y a bajo

costo. Finalmente, las figuras de mérito como el tiempo de programación

(escritura/borrado) y el tiempo de retención se presentan para obtener el

rendimiento de estos dispositivos de memoria.

Master thesis

Nanoparticles High-k dielectric thin films Semiconductor storage CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Strong and stable photoluminescence from the semiconducting inner tubes within double walled carbon nanotubes

Hiroyuki Muramatsu MAURICIO TERRONES MALDONADO Dresselhaus Mildred (2009)

"We examined the optical features of single wall carbon nanotubes (SWNTs) and the inner tubes within double walled carbon nanotubes (DWNTs) having the same (n,m) chirality. The brighter and more stable photoluminescence signals as well as the larger absorbance were observed for the semiconducting inner tubes within DWNTs and not for SWNTs. The outer layers of DWNTs maintain the high structural integrity of the inner tubes during both oxidative purification and strong sonication steps and are responsible in increasing the dielectric screening (due to weaker Coulomb interaction); thus leading to a redshift of the E(11)(S) and E(22)(S) excitonic transitions."

Article

Carbon nanotubes Chirality Elemental semiconductors Excitons Photoluminescence; Red shift Semiconductor nanotubes CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA