Nanodispositivos de GaN para generación de señales de THz. Simulación Monte Carlo y análisis experimental
[EN] OBJECTIVES The overall aim of this PhD Thesis is the numerical analysis (through simulation Monte Carlo, MC) and experimental (fabrication and characterization) of GaN-based nanodevices able to generate signals in the THz band. First, and by means of MC simulations, is to analyze the possibility of very high frequency oscillations by OPTTR in n + nn + diodes of GaN. It will investigate the conditions under which this phenomenon occurs and the influence of multiple parameters in achieving these oscillations, their frequency, amplitude and spectral purity. Second, in the scenario that provides excellent participation in a European project such as ROOTHz be studied intensively GaN SSDs for obtaining THz signals at room temperature by Gunn oscillations. Collaboration with other experimental groups, in this particular case the IEMN of Lille (France), will make it possible in this area, as well as MC simulations us dispose of fabrication and characterization of the devices studied, which should enable us to refine the models and contribute to the optimal design of SSDs to work as THz emitters. METHODOLOGY AND EXPERIMENTAL DESIGN The main tool used for the study that will take place in this thesis is the MC simulation of electronic devices based on a code entirely developed by the Research Group Semiconductor Devices, University of Salamanca. The first task of this work has been the adaptation of such a code in order to approach the study of GaN devices under this project. Although most of the results come from MC simulations, we also note that the result of collaboration with IEMN will present information on the fabrication and characterization of SSDs CONCLUSIONS OPTTR in n + nn + diodes of GaN When the operating temperature T is sufficiently low that the most likely mechanism of scattering in the network is the polar optical phonon emission, the dynamics of the electron transport through the active region of the diode consists of free flight of length l0, accelerated by the electric field, truncated by sudden slowdowns at the time of issuing the phonon. Along its cathode to the anode, electrons emitted phonon a number which depends on the potential applied to accelerate. The characteristic frequency of this phenomenon fE, reverse flight time between the emission of phonons, is proportional to the applied bias. The cyclic process stops and accelerations of all carriers resulting in charge accumulation in the braking zone. This will have an active region having a sequence of alternative accumulations positive and negative charge. The natural frequency of oscillation of such a charge density is the plasma frequency fp. If the frequency is close to fp fE, plasma oscillations are powered by quasi-synchronous input from electron charge buildup, and this gives rise to oscillations of high frequency current, next to, through the device . For this to occur, it is also necessary that the spacing between the charge accumulations, l0, is much greater than the Debye length. Gunn oscillations in GaN-based SSDs As other III-V materials, the GaN has, from a field threshold around 200 kV / cm, an area of negative incremental mobility. Their origin is the transfer of electrons from the valley to valley U 1, which gives them a greater effective mass and, therefore, slows them down, may form charge accumulations that propagate through the material to the saturation velocity. Known as Gunn effect, this phenomenon can be exploited to obtain oscillations in the current. The fact that the present GaN high values on the one hand, the threshold field and the breakdown field and, secondly, the saturation velocity, makes it a promising element of power devices and high frequency that exploit Gunn effect. The simple geometry of the diodes SSD, transport devices where ditches insulating planar L-shaped break channel asymmetry is favorable for the emission of signals by effect Gunn THz at room temperature. Increased noise at low frequency as an indicator of the oscillations Since experimental techniques at frequencies of hundreds of GHz are still remarkably complicated, there is the need for alternative methods for detecting the presence of oscillations in the THz range or sub-THz MC predicting simulations. The kinks associated with the onset of instabilities, which in some cases are detected in the oscillator device IV curves indicating the transition from a passive state to a state of generation, in the diodes studied in this work are unclear (in n diodes + nn + for OPTTR) or even absent (in SSDs). However, MC simulation results for the spectral density of the noise in a low frequency current IS (0) show that it presents a very marked increase in the potential applied when approaching the threshold for the appearance of the oscillations
Academic dissertations, Semiconductors, Diodes, Semiconductor, Microelectronics, Monte Carlo method, GaN, Tesis y disertaciones académicas, Universidad de Salamanca (España), Tesis Doctoral, Semiconductores, Diodos semiconductores, Microelectrónica, Monte-Carlo, Método de, Nitruro de galio
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