This project is concerned with the identification and localization of the causes for the limitation of the optoelectronic performance data of semiconductor nanowire structures. The aim is to achieve an intensive correlation of macroscopic device data with spatially very high resolution microscopy data. The devices feature axial and coaxial nanowire homo- and hetero-contacts for charge separation, consisting of GaAs- and InGaP-based pn-contacts, which are fabricated by MOVPE. The relationship between interface formations and recombination paths will be determined by a combination of in-system four-point measurements, scanning probe microscopy and optical methods. The current-voltage characteristics of upright axial versus radial nanowire structures as well as high-resolution scanning tunnelling microscopy will be measured locally. The investigation of the optoelectronic properties is performed with a streak camera system. The metrological detection and localization encounters inherent limitations in nano-devices, which are therefore processed for physical modeling using the simulation software package Silvaco Atlas. The performance data for the determination of conversion efficiencies are determined taking into account generation and recombination mechanisms as well as minority and tunnel transport across homo- and hetero-junctions.
The project goal is to determine the qualitative and quantitative relationship between nanowire growth, device design, interface formation and surface passivation with respect to the quality of charge-separating pn-junctions in nanowires. From this, concepts are to be presented and tested which allow a significant increase in optoelectronic performance characteristics in light-nanowire interaction.
