Ultrafast optoelectronics in III-V semiconductor nanowires

In this thesis, we investigate the ultrafast photocurrent response of semiconductor nanowires to advance the development of ultrafast and small nanowire photo-switches. Semiconductor nanowires have gained a great amount of attention in research as they are suitable building blocks for future optoelectronic and highly integrated devices such as an optical computer. In order to enable applications in optoelectronics, we investigate the photocurrents in III-V semiconductor nanowires using a THz-time domain photocurrent spectroscopy. Using this technique we measure the photocurrents in single nanowires with a picosecond time resolution. We examine the photocurrents in p-doped GaAs nanowires and in intrinsic InAs nanowires. Moreover, we study the optoelectronic response in two nanowire heterostructures. The first one consists of a n-type InGaN nanowire with a linearly graded In content along the nanowire axis. The second one comprises a AlGaAs/GaAs quantum well nanowire containing a 2 nm GaAs quantum well in the AlGaAs shell. All four investigated nanowire geometries exhibit an ultra-fast photocurrent response with a FWHM of (1 − 3) ps. Therefore, these nano- wires are suitable as functional parts of ultrafast photo-switches. We observe that single InAs nanowires emit THz radiation after pulsed laser excitation due to a photo-Dember effect. Therefore InAs nanowires are good candidates for nano- THz sources in integrated devices. Finally, we find a new photocurrent behavior for linearly graded InGaN nanowires which we name “negative differential photocurrent.” The unique band alignment within these InGaN nanowires leads to a sign change in the photocurrent, if the exciting laser power is increased. Our findings contribute to a better understanding of the optoelectronic properties of semiconductor nanowires.