We study the semiclassical and quantum transport properties of the two-dimensional electron system in GaAs/AlGaAs semiconductor heterostructures under a perpendicular magnetic field. We studied two different samples, A and B under different experimental frameworks. For sample A, we mainly probe the applicable range of the Shubnikov-de Haas (SdH) theory when the thermal damping is reduced with decreasing temperature. We found the applicable range of the SdH theory can be extended, and the positive magneto-resistance and the disorder-induced damping play important roles. In the experiment of sample B, we removed the influence of thermal resistance by measuring forward and backward currents. We found the semiclassical Lifshitz-Kosevich formula in the SdH theory is more robust in describing the magneto-oscillations. Surprisingly, we found the existence of the mobility gap, which indicates the quantum Hall effect. The semiclassical behavior is attributed to the electrons away from the tails of Landau bands. Our study hints that we shall consider the quantum diffusion model to modify the Dingle term.

We have studied the electronic properties of InGaAs/AlInAs nano wire by using Shubnikov-de Hass (SdH)measurement at 0.3K.In order to study the effect of the channel width on the 2DEG,we made the nanometer-scaled 2DEG channels varied with different widths from 700 nm to 1400 nm by focus ion beam. On the AlGaAs/AlInAs nanowires we have studied I-V characteristics with gate-voltage and observed the work range from -3 V to 3 V. After illuminating at 0.3 K, the carrier density of the sample InGaAs-1400 nm increased and observed the persistent photoconductivity effect. After SdH measurement at 0.3 K, we found saturation current of these samples at 77 K but did not observe change with different gate voltage.

We have fabricated the device of High Electron Mobility Transistor(HEMT) on Al0.18Ga0.82N/GaN heterostructures. The mobility of 2DEG of the AlGaN/GaN is 9328 cm2/Vs and carrier concentration is 7.917 1012 cm-2 obtained by conventional van der pauw Hall measurement at temperature of 77 K. We made the conducting channel of nanometer wires on the AlGaN/GaN heterostructures for researching low-dimensional transport of two-Dimensional Electron Gas by gate controlled. From the SdH measurement, we can clearly observe the SdH oscillations and obtain the SdH frequencies. For the sample of 0922GaN-200 nm and 0922GaN-100 nm at 0.39 K,two constituted peaks of Gauss¡¦s function were fitted by Non-linear Curve and Two SdH oscillations beat each other, probably due to spin-splitting. However, we can¡¦t discover any trend in the experiment of gate controlled. In the future, we will try to improve the quality and discover the suitable depth of SiO2.

In this thesis, we study the magnetro-transport properties of Fe-doped AlxGa1-xN/GaN heterostructure with different Al content by Shubnikov-de Haas measurements. On the samples KTH640(x=0.294)¡BKTH643(x=0.344)¡BKTH642(x=0.390)¡BKTH644 (x=0.397), we find that the electron have occupied the lowest two subbands, and the energy separation for each sample before illumination is 98 meV¡B107 meV¡B111 meV¡B119 meV. On the samples KTH641(x= 0.216)¡BKTH640(x= 0.294)¡BKTH642(x= 0.390)¡BKTH644(x= 0.394), we observe the electrons have spin splitting phenomenon, and the highest spin splitting energy separation¡¦s value in our experiments is 10.6 meV. For all six samples have persistent photoconductivity effect¡¦s behavior after illumination.

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High efficiency components are key elements of solid-state amplifiers for wireless application. We used HEMT (high-electron-mobility transistor) to obtain high mobility 2DEGs. AlGaN makes itself an attractive material for high frequency devices, and the system is particularly good for the investigation of quantum Hall effect. We studied the electronic properties of AlxGa1-xN/GaN heterostructures by using Shubnikov-de Haas (SdH) measurement. The T-dependent Hall measurement (from 4.2 K to 300K) was performed at the magnetic field 0.3T and the B-dependent Hall measurement (from 0.02T to 0.8 T) at constant temperature. From the field-dependent Hall measurements, we are able to calculate the individual mobility and carrier concentration for the two-subband-populated AlxGa1-xN/GaN heterostructures. Then, we can use T-dependent Hall effect measurement to calculate the binding energy of the deep-level trap Ed,which is a measure of the energy constant for the ionization of deep-level trap in thermal equilibrium.

We have studied the electronic properties of AlxGa1-xN/GaN heterostructures by using Shubnikov¡Vde Haas(SdH) measurement. Two SdH oscillations were detected on the sample of x=0.31, due to the population of the first two subbands with the energy separations of 94.2 meV. For the samples of x=0.22 and x=0.23, two SdH oscillations beat each other, probably due to a finite zero-field spin splitting. The spin-splitting energies are equal to 1.4~5.3 and 4.5 meV . The samples also showed a persistent photoconductivity effect after illuminating by blue light-emitting diode.

We discussed the electronic properties in AlxGa1-xN/GaN heterostructures. There are six different samples of AlxGa1-xN/GaN we prepared for this experiment, three of them are undoped AlxGa1-xN/GaN with different x values which is 0.17, 0.29 and 0.33, respectively. The others are Fe-doped AlxGa1-xN/GaN which the x value is 0.18, 0.19 and 0.21 for each sample. Comparing these two types¡¦ materials¡¦ results, we tried to confirm the impurity¡¦s characteristic in our samples. From the Hall measurement results, carrier concentration of Fe-doped AlxGa1-xN/GaN were pretty lower than undoped AlxGa1-xN/GaN, and the mobility at 4.2 K are almost two times to undoped AlxGa1-xN/GaN. At the same time, we performed Shubnikov-de Hass measurement, and two subbands of the 2DEG were populated on the samples for x value is 0.29 and 0.33. The energy separation for first two subbands is 109meV. We also observed obvious beat pattern in the SdH oscillations due to the spin splitting on the samples and the greatest spin-splitting energy is 5.96meV in our measurement. Furthermore, we observed evident PPC effect on the samples of Fe-doped AlxGa1-xN/GaN, the carrier concentrations increased at least 23% after illumination. Meanwhile the samples of undoped AlxGa1-xN/GaN can just produce 10.7% increment at most.

We have studied the electronic properties of InxGa1-xAs/ In0.52Al0.48As quantum wells by using Shubnickove-de Hass (SdH) measurement. The indium composition (x) of well layers was varied from 0.5 to 0.56 whit different structures, such as sample A is simply ¡§In0.53Ga0.47As¡¨, sample B is a step-well like¡§In0.56Ga0.44As/In0.53Ga0.47As/In0.5Ga0.47As¡¨,sample C is linearly graded well is a opposite way¡§In0.56Ga0.44As down to In0.5Ga0.5As, and sample D is linearly graded well ¡§In0.5Ga0.5As up to In0.56Ga0.44As.¡¨ It was found that the two SdH oscillations beat each other due to the population of the lowest two subbands in these samples. In order to investigate the electronic properties of the two subbands, we have done the Ven der Pauw Hall measurement . From SdH and Hall measurement, we are able to determine the individual mobility and carrier concentrations for two-subband-populated samples.

Las empresas operadoras están enfrentando cambios radicales en el modelo de negocio. Sus clientes ya no contratan enlaces a redes porque ellos buscan servicios. Actualmente, los grandes sistemas de transporte digital, tanto urbanos como de larga distancia e internacionales, se basan en SDH (Synchronous Digital Hierarchy), las cuales son optimas para tráfico de voz pues están diseñadas para conmutar circuitos. Sin embargo, la conmutación de paquetes es la que ha experimentado un crecimiento exponencial y las empresas deben hacer frente a este proceso. El protocolo IP ha sido sin dudas el gran gestor de sistemas de valor agregado, mostrándose en franca consolidación y expansión. En respuesta a lo anterior, las plataformas actuales, compuestas por tecnologías variadas y muchas veces propietarias, deben evolucionar hacia estructuras más flexibles, dinámicas y, sobre todo, integradas y optimizadas para manejo robusto de tráfico paquetizado. El objetivo principal de este trabajo es proponer una tecnología de transporte digital que permita llevar a efecto la evolución de las tecnologías de transporte rentabilizando los recursos, migrando los servicios de manera transparente, y permitiendo la escalabilidad para soportar las nuevas demandas de ancho de banda y prestaciones. Otro de los objetivos es mejorar la operación, simplificando las tareas de gestión, habilitación, provisión y mantenimiento. Las etapas para lograr lo planteado son cuatro: estudio teórico de la recomendación G.ASON (Automatic Switched Optical Network) de la ITU (International Telecommunication Union) y del estándar GMPLS (Generalized Multiprotocol Label Switching) de IETF (Internet Engineering Task Force); análisis técnico de las redes y protocolos en operación para voz, datos y otros servicios; especificación y propuesta de prototipo a escala de la solución; y, ejecución práctica e implementación de la maqueta de prueba para validar su funcionamiento. Este trabajo demuestra la aplicabilidad de ASON/GMPLS como nuevo estándar de transporte digital porque resuelve la problemática presente y capacidad para abordar los retos futuros: aumento drástico y escalable del ancho de banda; soporte de los servicios de manera transparente ya que es compatible con elementos multiservicios; fuerte crecimiento de los indicadores de disponibilidad de la red; simplificación de la provisión, habilitación, gestión y mantenimiento pues muchas de estas tareas son facilitadas por el plano de control distribuido de la tecnología ASON; y, explotación de la capacidad ociosa de enlaces, sin afectar la calidad de servicio comprometida. Además, este proyecto de título entrega un modelo conceptual, teórico y práctico para la implementación de ASON, aporta al conocimiento operativo de los dispositivos tecnológicos, contribuye a la creación de un plan de migración de las redes existentes y define requerimientos a exigir de los proveedores de equipos. La tendencia futura apunta hacia aplicaciones IP. En el núcleo de red de transporte, ASON basado en SDH mantendrá la supremacía. Esta tecnología será fortalecida con sistemas de gestión altamente inteligentes que permitirán inventario, provisión y reorganización de circuitos de manera totalmente automatizada.