Surface modification of optoelectonic devices with gallium nanoparticles

Resumen

This work aimed to the investigation and develop material surface modification procedures with the use of gallium nanoparticles (Ga NPs). Firstly, a new method to produce Ga colloids in different solvents was designed. The NPs were thermally evaporated on an aluminium zinc oxide (AZO) expendable layer to be transferred later to the solvent such as tetrahydrofuran (THF), deionized water (DIW) or ethanol (EtOH). The sample allowed to investigate the characteristic surface and bulk plasmonic absorptions of the growth NPs. Once determined the intrinsic optical property of the Ga nanostructures, the thesis work focused on the study of plasma and chemical treatment for shaping and tuning NPs arrays. By means of dry etching process, nanocone structures were obtained. The reshaping process was based on the height/diameter (h/d) ratio figure of merit. Comparing to the unmodified NPs, the smaller the h/d, the higher the light absorbed value as also confirmed by far field simulations. Further analytic calculation of different h/d ratios demonstrated up to two fold enhancement of the near field around the modified structure. Additionally, the Ga NPs were also used to fabricate Si nanocolumns with a Ga cap. The exotic shape guaranteed remarkable antireflective coating property, especially in the near infrared range. Since the surface modification strongly depends on the NPs coverage density, our study found that chloridric acid wet etching – a compatible method with many microelectronic processes - can easily control this parameter. Finally, Ga NPs were applied on an InGaAs/InAlAs avalanche photodiode surface jointly to a polymethylmethacrylate (PMMA) passivation layer. The latter helped as a buffer layer between the Ga and the mesa to stop conduction phenomena and reducing the leakage current contribution. Additionally, samples were thermally treated to tune the NPs layer physical composition, hence their effective permittivity. The treatment led to almost 30 % enhancement of the device light current generation. This thesis received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 641899.