Scanning probe techniques as an investigation tool for semiconductor nanostructures and devices

Abstract: Semiconductor nanostructure based devices provide new opportunities for contributing to a sustainable energy usage. This includes harvesting of energy (solar cells) and saving of energy, e.g. in lighting (light-emitting diodes, LEDs) and transfer of energy (power devices). However, development and improvement of nanostructure devices requires thorough characterization and understanding on a single nanostructure level. At nanometer dimensions, surface effects start dominating device performance. Therefore, macroscopic bulk characterization techniques are insufficient, and surface-sensitive tools are needed. Here, I used various types of scanning probe microscopy to investigate and manipulate surface and material properties of nanostructure devices that are relevant for energy saving and harvesting.In(Ga)P nanowire diodes are promising candidates for photovoltaic applications. Kelvin probe microscopy (KPM) and scanning tunneling microscopy (STM) were used to investigate surface band alignment of a nanowire p-n junction. In addition, a novel method for optoelectronic characterization of individual nanowires without any processing steps is demonstrated. STM was utilized to both image and contact individual upright standing InGaP nanowires, obtaining current-voltage characteristics and solar cell figures of merits in dark and under illumination, for as-grown nanowires and after in-situ surface modification.InGaN nanostructures are attractive for LEDs, because the luminescence of InGaN alloys could potentially cover the entire visible range by tuning the In content. The nanowire geometry allows combination of lattice mismatched materials. Nanowire-based InGaN platelet LEDs with varying In content as well as In quantum dots were studied by atomic force microscope (AFM), correlating surface corrugation with optical properties and investigating nucleation of surface facets.GaN offers principally superior material properties for power electronic devices compared to the currently used Si and SiC, but a reduction of the defect density is required. We investigated low-defect GaN planar layers formed by reformation of GaN nanowire arrays. AFM, conductive-AFM, KPM, and scanning capacitance microscopy were utilized to investigate formation and distribution of different types of defects and their influence on GaN electrical properties. Furthermore, the revelation of defect-related conductive paths through AFM-induced anodic oxidation was explored.