Characterization of single InP Nanowire-based Avalanche Photodetectors

Nanoscience is an emerging field of technology where the bottom-up fabrication techniques are utilized instead of the traditional top-down approaches for enhancing the performance of di erent optoelectronic devices. One such material is a semicon- ductor nanowire (NW) which holds immense potential in nanophotonic applications, such as solar cells, LEDs, lasers, sensors and photodetectors. In particular, detec- tion of infrared (IR) radiation emitted by all bodies has wide applications in medical imaging, environmental monitoring, surveillance, security and optical communica- tion. This Bachelor’s thesis fits in the purpose of developing novel devices which is part of a bigger project, aiming towards the fabrication and integration of e cient InP/InAsP NW Avalanche Photodetectors (APD). The NWs are designed with a Separate Absorption Multiplication (SAM) geometry in a vertical array pattern, but for a fundamental understanding single NWs are contacted in lateral geometry and characterized individually. The characterization setup used is a Cascade 11000B probe station equipped with a Keithley 4200 semiconductor characterization module. Our e orts were focused on determining experimentally the breakdown voltage for two di erent samples of NW APDs, as an initial step of establishing the dependance of the breakdown voltage with the temperature. A study of the contacts was also addressed in order to provide more data to the design of an optimized ohmic contact in the p-segment of the NWs. We could demonstrate that growing NWs with longer p-segments overcome the contacting issues previously reported. Additionally, we could recognize the influence on our results of the Schottky barrier present in the contact with the p+-segment, especially in the values obtained for the ideality factor (n = 1.2 ± 0.1 and n = 1.53 ± 0.12). Therefore, we conclude that optimizing the p-segment contact should be prioritized on further research. Finally, regarding the avalanche processes, the measurements performed were successful and in agreement with previous research on other materials. Nevertheless, the values obtained for the breakdown voltage (Vbr ≥ ≠45V on average) should be complemented with more measurements within the same samples, and with analysis on devices with di erent dopping profiles, in order to have a more reliable result and a trend in our data.NANO, THE FUTURE OF TECHNOLOGY? A deeper look on Nano-photodetectors. Photodetectors are like the transmission of a formula one car; they are not as fancy as the aerodynamics design, or not as famous as the engine, but they are crucial for the car performance. So, what are photodetectors and why should we care about them? This are devices capable to detect electromagnetic radiation and convert it into an electric signal. What make them interesting and useful is that we are capable to make them detect a specific radiation, like infrared light for example, so their applications can range from simple devices that automatically open supermarket doors and receivers on TV remote controls, to photodiodes in fiberoptic connections or in Integrated Circuits, which are present in virtually all electronic equipment that we use today. Modern technology is pursuing the challenge to do smaller, lighter and more efficient components, and nanotechnology is proving to be the way to do it. When we talk about nanodevices, we have to think about how the size of a typical nanoparticle is to that formula one car as the car is to the Earth, and at that size things do not work the way we are used to; it is the territory of Quantum physics, and materials present a whole new set of characteristics that we can use to improve our technology. In the case of photodetectors, it is theoretically possible that nanowire arrays reach 100% light absorption. This could make the creation of 100% efficient solar panels possible (the actual performance of a solar cell is around 30%). However, in order to reach all these applications and improve the present technology, a better knowledge of the behavior of these nanowire-based devices has to be reached. This will be the aim of this thesis: we are going to characterize a specific configuration for an indium phosphide nanowire-based photodetector. By determining its behavior under different voltages and temperatures and comparing two different configurations, we want to reach a basic knowledge of this devices, which will set a starting point on the pursue of a more efficient photodetector design