| AVS 64th International Symposium & Exhibition | |
| Novel Trends in Synchrotron and FEL-Based Analysis Focus Topic | Tuesday Sessions |
| Session SA+AS+HC+SS-TuA |
| Session: | Frontiers of Photoelectron Spectroscopy: Surface & Interface Processes with Variable Depth Probe, High Spatial or Temporal Resolution |
| Presenter: | Andrea Troian, Lund University, Sweden |
| Authors: | S. McKibbin, Lund University, Sweden A. Troian, Lund University, Sweden S. Yngman, Lund University, Sweden H. Sezen, Elettra-Sincrotrone Trieste, Italy M. Amati, Elettra-Sincrotrone Trieste, Italy L. Gregoratti, Elettra-Sincrotrone Trieste, Italy A. Mikkelsen, Lund University, Sweden R. Timm, Lund University, Sweden |
| Correspondent: | Click to Email |
III-V semiconductor nanowires (NWs) have a large technological potential within electronics, optoelectronics, and energy harvesting [1,2], mainly due to their flexibility in creating heterostructures by axial stacking during epitaxial growth. Because of their small diameter and their very large surface-to-volume-ratio, the performance of NW devices is strongly determined by surface properties. X-ray photoemission spectroscopy (XPS) has been proven highly suitable for studying surface composition and electronic properties of homogeneous NWs [3]. However, in order to better understand NW device performance, it is essential to also investigate NW heterostructures, with nm-scale lateral resolution and during device operation.
Here, we will present nano-focus XPS results from material and doping heterostructures in InP and GaInP NWs intended for photovoltaic application [2]. We used scanning photoemission microscopy (SPEM) at the ESCAMicroscopy beamline of the ELETTRA synchrotron, providing a lateral resolution of about 120 nm, for imaging individual NWs. In addition, we revealed the change in local surface potential across (Ga)InP pn-junctions and InP/GaP tunnel junctions, obtained from In 3d, In 4d, and P 2p XP spectra acquired along the heterostructure NW. Electrical contacts were provided to both ends of the investigated NW, allowing to vary the source-drain bias along the NW during SPEM characterization. We will present detailed results on the influence of built-in potential and external forward and backward bias on the surface potential distribution across NW interfaces.
In another approach, we aim at revealing in-situ the interplay of surface chemical composition and local electronic properties. As a model system, we chose InAs NWs consisting of several segments of wurtzite and zincblende crystal structure [4]. At the interface between such segments, we confirmed a staggered type-II electronic band alignment, obtained from nano-focus XP spectra along externally biased NWs. After removing the native oxide from the NW surface by atomic hydrogen annealing [4] in the XPS UHV chamber, the same NW instead showed flat-band conditions, which is preferential for electronic application [1]. We will discuss future plans of using the dynamic high pressure option of the ESCAMicroscopy beamline for changing the surface chemistry of NWs while simultaneously investigating them with SPEM and nm-scale spectroscopy.
[1] E. Lind et al., IEEE J. El. Dev. Soc. 3, 96 (2015).
[2] J. Wallentin et al., Science 339, 1057 (2013).
[3] R. Timm et al., Appl. Phys. Lett. 99, 222907 (2011); J. Webb et al., Nano Lett. 15, 4865 (2015).
[4] M. Hjort et al., ACS Nano 8, 12346 (2014).