Abstract
This thesis aims at the investigation of novel semiconductor materials by using non-destructive optical and electrical spectroscopic measurement techniques and a comparison of the results with theoretical models. Chapter one will give a brief introduction into the topic of optical communication and explain the motivation behind this thesis. The second chapter will then summarise the theory necessary to understand the photo-voltage (PV), photo- and electro-luminescence (PL and EL), reflectance (R), modulation spectroscopy (MS), and modulation bandwidth experiments, which is illustrated with some examples. The third chapter will then describe the utilised experimental set-ups. The fourth chapter will discuss GaAsSb quantum wells (QWs), which are thought to be suitable as emitters in VCSELs emitting at 1. 3um for future fibre-to-the-home applications. Here especially the GaAsSb/GaAs band alignment will be studied using PL and MS experiments in comparison to a simple QW model, thus inferring a weak type-II alignment. It will also show how the uncertainty is reduced, by a direct comparison of measured electroabsorption (EA) spectra with calculated EA spectra, which are obtained by collaborators using a detailed microscopic model. Thus, it will describe how the comparison leads to a value of 40meV +/-20meV type-II for the GaAsSb/GaAs conduction band offset. The fifth chapter will then present results of MS and EL of a full fledged VCSEL structure with GaAsSb QWs. Here the main focus will be on the investigation of the alignment of energy positions of the QW and the cavity mode, and a comparison of the results to parallel device measurements by collaborators. The sixth chapter deals with the new GaNPAs material grown on GaP, which has potential to lead to integrated optics in Si. It will give preliminary PL and MS results of edge-emitter structures and compare them to a simple QW model. The seventh chapter will then look at GaN-based AlGalnN RCLEDs aimed at plastic-optical fibre based bus systems for automobile and avionic applications. It comprises a study of the built-in electric field of the QW, using a comparison between electroreflectance measurements and a simple QW model; as well as studies of the EL and the carrier lifetimes in comparison to existing AlGalnP RCLEDs. The eighth and last chapter contains a summary of the conclusions and some future perspectives.