Resistive Switching in Nano-Optoelectronic Devices: Towards an Optical Memristor
[eng] Resistive switching devices have been a topic of great interest in the last two decades, as they could lead the next generation of memories and processors. These devices present a behavior that allows them to modify their electrical resistance between two or more states and retain them without...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/189855 |
| Acceso en línea: | https://hdl.handle.net/2445/189855 http://hdl.handle.net/10803/675676 |
| Access Level: | acceso abierto |
| Palabra clave: | Semiconductors Fotoelectricitat Nanoelectrònica Dispositius optoelectrònics Photoelectricity Nanoelectronics Optoelectronic devices |
| Sumario: | [eng] Resistive switching devices have been a topic of great interest in the last two decades, as they could lead the next generation of memories and processors. These devices present a behavior that allows them to modify their electrical resistance between two or more states and retain them without the need for external energy. The possibility of having two resistance states (high resistance interpreted as 0 and low resistance as 1) already serves as a digital memory, with the advantage of faster switching speeds, lower dimensions for single devices and lower power consumption, when compared to current memories. Since their first physical realization in 2008, great advances have been made in terms of materials employed, device structure, modelling and integration and scaling into arrays and chips. In addition, the properties of resistive switching devices have opened the door for other applications beyond pure memory and the conventional von Neumann architecture. Within the context of resistive switching research, this Doctoral Thesis proposes one new field that can be benefited in the future by the inclusion of such devices: Optoelectronics. The main objective of this Doctoral Thesis is the development of a new concept of devices, which we have called optical memristors. Two types of devices have been attempted and realized: memristors with light emission or absorption. Notwithstanding, both had a particular requirement: transparent materials where necessary for light to be transmitted not only through the electrodes but also through the active layers of the devices. The first approach to light emitting memristors presented explores the possibilities of light emitting devices based on rare earth ions. These elements are commonly employed in displays for the fabrication of phosphorus layers that are excited by a blue emitting device. When properly used as dopants, these elements are optically active and can be electrically excited within a matrix of an oxide material. Thus, the emission of such devices based on Al/Tb/Al/SiO2 layers is studied. A reduction of emission efficiency is also identified with resistive switching capabilities of these devices, though a low number of cycles is possible. A second approach starts from an already transparent conductive oxide (TCO) that has shown resistive switching properties in the literature: ZnO. This material presents advantages when compared to the most employed TCO, ITO, in the form of a non-toxic and abundant compound. In addition, it can be doped with rare earth ions that are optically active. In the same way as the previous approach, resistive switching of these devices is possible, but the inclusion of rare earth ions highly diminishes their endurance. Finally, a different strategy allows for the objective results to be achieved. Silicon oxide is employed as an already reported material with resistive switching properties, where Si nanocrystals (NCs) are embedded as luminescent centers. Their combination results optimal for the target application, yielding durable devices with differentiated emissions dependent on the resistance state and that avoid its overwriting when read. Furthermore, the range of optical properties that become available to these devices through the presence of Si NCs is extended to that of light absorption. The devices become optically-readable taking profit of the photovoltaic effect of their tandem solar cell structure, distinguishing high and low current extractions dependent on the resistance state. Last, the effect of resistive switching and the presence of conductive filaments in these solar cells is explored, achieving increased efficiencies when compared to pristine devices. |
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