| AVS 65th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Wednesday Sessions |
| Session EM+AN+MI+SS-WeM |
| Session: | Surface and Interface Challenges in Electronics and Photonics |
| Presenter: | Rainer Timm, Lund University, Sweden |
| Authors: | J. Colvin, Lund University, Sweden A. Troian, Lund University, Sweden O. Persson, Lund University, Sweden 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. We have previously studied surfaces and surface oxides of semiconductor NWs by scanning tunneling microscopy and spectroscopy (STM/S) [3] as well as X-ray photoemission spectroscopy [4]. Here, we will correlate the surface properties of InAs and InP NW heterostructures with their electrical and photovoltaic behavior, which has been measured for individual upright-standing NWs using the STM tip as local nanoprobe [5].
InP and GaInP pin-junction NWs have been cleaned from their native oxide by annealing under atomic hydrogen background and re-oxidized by exposure to ambient conditions. By illuminating the InP NWs that were contacted by the STM nanoprobe, we observed a decrease of the open-circuit voltage from 0.75 V to 0.70 V upon native oxide removal and an increase back to 0.76 V upon re-oxidation, confirming the need of surface passivation for improving InP solar cells. However, the ideality factor of the NW pin-diodes remained constant at n = 1.82 upon oxide removal, but improved to n = 1.67 upon re-oxidation. Furthermore, our XPS results indicate the outdiffusion of Zn dopants from the p-doped NW segments, forming a Zn-rich shell around the NW.
A more significant effect of the presence of native surface oxide was found for InAs NWs which consist of one segment of wurtzite and one segment of zincblende crystal structure. Upon removal of the native surface oxide, we obtained an increase in conductivity of these NWs by two orders of magnitude, while reference NWs with pure wurtzite structure showed a slight decrease in conductivity with the same surface treatment. This effect can be explained by a staggered type-II surface band alignment at the wurtzite/zincblende interface of oxidized NWs, which turned into flat-band conditions upon oxide removal, as confirmed by nano-focus XPS measurements.
[1] E. Lind et al., IEEE J. El. Dev. Soc. 3, 96 (2015).
[2] J. Wallentin et al., Science 339, 1057 (2013).
[3] M. Hjort et al., ACS Nano 8, 12346 (2014).
[4] R. Timm et al., Appl. Phys. Lett. 99, 222907 (2011); J. Webb et al., Nano Lett. 15, 4865 (2015).
[5] R. Timm et al., Nano Lett. 13, 5182 (2013).