STM-based characterization of single GaInP photovoltaic nanowires

Abstract: The I-V and photovoltaic properties of III-V semiconducting GaInP nanowires have been studied using a scanning tunneling microscope (STM) in evaluation for usage as a potential "sub cell" in a nanowire based tandem solar cell configuration. This evaluation required precise I-V characterization and photo response measurements of individual nanowires. Such measurements usually involve rigorous sample preparation, establishing metal contacts on both ends of the nanowire, which might have an inhibiting effect on the measured currents. In this work another approach has been employed allowing reproducible measurements on single upright standing nanowires. Using a standard STM, Ohmic contacts have been established with the Au seed particles of the GaInP nanowires. This reduced negative effects from the metal-semiconductor interfaces and required no sample preparation. In this way successful I-V characterization was conducted with currents in the µA range resulting in an average ideality factor of 2.04±0.08. Through laser illumination photocurrents of 19.3 pA were reached and a maximum open circuit voltage (Voc) of 0.98 V. Furthermore, this thesis presents measurements of the band gap (1.95 eV) and atomic imaging of the surface structure of GaInP nanowires which have not yet been reported in literature. These results could be useful in the creation of a nanowire based tandem solar cell with GaInP (with a large measured band gap of 1.95 eV) as a potential top cell in a tandem configuration with InP (1.34 eV) which has been studied to a great extent in the past. The attained results could also be of interest for further studies of GaInP nanowires in other purposes.