L'exploitation et l'amélioration des propriétés optiques et électriques du germanium pour la conception et la réalisation de dispositifs de mesures optoélectroniques

Abstract

Based on current energy context, the requirements regarding the accuracy of radiometric instruments are becoming increasingly critical and the materials needed for devices converting energy into an electric current gives rise to numerous research and development. All this, implies that these materials should be more efficient from the point of view sensitivity to temperature change and light radiation. The sensitivity of a device for radiometric measurements is the ratio between the output which is the electric current and the input which is the incident light power. The latter is also expressed in terms of the material’s reflection coefficient and the quantum efficiency. This project was carried out with the aim of improving these two parameters by exploiting the structural properties of Germanium to first improve its optical characteristics and for the potential improvement of its electrical ones. Most of the project was devoted to the optical reflectance of this material. Indeed, research has been conducted with the aim of establishing an original and low cost-effective method of etching allowing the porosification of the device active surface and thus increasing the surface to air ratio to trap the incident photons and create more electron-hole pairs. Different treatments have been tested which are all chemical-solution based baths. The treatment that encouraged us to do further investigation is the aqua-regia treatment since the observation of its results under the Scanning Electron Microscopy (SEM) showed homogeneous and shallow V-shaped nanotextured pit arrays. A more precise topographic analysis by studying the influence of the bath time using an Atomic Force Microscope (AFM), a crystallographic analysis using the XRay Diffraction technique (XRD) and analysis of optical reflection using the UV-VIS-NIR spectroscopy have been conducted in order to understand the nature and the behavior of the etched surface. The conclusion of this analyzes was that the aqua regia treatment allowed not only the porosification of the surface in a controllable way while maintaining its crystalline structure but also showed that rapid treatment of 5min immersion could reduce the reflection by 12-14% compared to bulk Ge and a one-hour treatment could reduce reflection under 14%. Another part of the project focuses on the design and the implementation of a Germanium photodiode PN-junction based. This step was carried out with the aim of identifying all the points to be considered and to be checked during the realization process of a PN junction photodiode and with the aim of commenting on the anomalies detected in this first embodiment in order to be able to improve them in the future. To facilitate the collection of the generated electrons by the external circuit and to prevent the recombination of the charged carriers to improve the quantum efficiency, the implantation parameters of the doped layer for the formation of the PN junction were chosen in the basis of the simulation and the bibliography allowing the upper layer of the device to be highly doped and close to the surface. The quality of the realized implantation was then discussed. Also, the choice of metals for electrodes deposition has been made in such a way to make possible, an ohmic contact formation. On the other hand, the upper electrode must meet the requirements of transparency and conductivity, which has led to a study of the shape of the upper electrode. The realization of the crude Gebased photodiode with this configuration will allow us later, after the characterization of the porous layer, to make another similar photodiode, but based on porous Ge. The definition of the Germanium PN junction photodiode’s configuration with all its parameters and the characterization of the porous layer allow us to select the appropriate engraving parameters to propose the integration of this porosity on the front face of the Germanium photodiode.

Date	24 Jul 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Sylvain G. Cloutier (Supervisor) & Oualid Touayar (Co-supervisor)