In our studies of nanowire properties, we pay special attention to phenomena that are a direct consequence of the peculiar wire-like shape and nanometric size and are independent of the material the nanowires consist of. For example, the high surface-to-volume ratio of nanowires has several important consequences. In particular, lattice-mismatched axial heterostructures relax their strain elastically at the free sidewalls, and the formation of dislocations is avoided. For radial heterostructures, a new type of structure only possible due to the nanowire geometry, the strain is shared between core and shell. In both cases, the strain distribution is very complex. Since many semiconductor properties depend sensitively on strain, the dedicated investigation of strain in nanowires is crucial for an understanding of their optoelectronic properties.

Another consequence of sidewall surfaces are radial electric fields induced by surface states. The strength of these fields depends on the doping density in the nanowire and may be large enough to dissociate excitons. Electric fields and doping crucially affect device design and are thus important topics of investigation.

Furthermore, nanowires are not ideal single crystals but exhibit structural defects. Some of these defects, such as twin boundaries, stacking faults, and inversion domain boundaries, act as two-dimensional radiative defects that may dominate luminescence. Others, such as dislocations created by the coalescence of nanowires in close vicinity, act as nonradiative defects. Nonradiative recombination also occurs at the free surface or interfaces and at point defects. Investigations of the microstructure and internal quantum efficiency are thus essential to elucidate the actual potential of group III-V nanowires for optoelectronic applications.


Selected publications

Author: C. Sinito , P. Corfdir , C. Pfüller , G. Gao , J. Bartolomé , S. Kölling , A. Rodil Doblado , U. Jahn , J. Lähnemann , T. Auzelle , J. K. Zettler , T. Flissikowski , P. Koenraad , H. T. Grahn , L. Geelhaar , S. Fernández-Garrido , O. Brandt
Title: Absence of quantum-confined Stark effect in GaN quantum disks embedded in (Al,Ga)N nanowires grown by molecular beam epitaxy
Source: Nano Lett. , 19 , 5938 ( 2019 )
DOI: 10.1021/acs.nanolett.9b01521

Author: J. Lähnemann , M. O. Hill , J. Herranz , O. Marquardt , G. Gao , A. Al Hassan , A. Davtyan , S. O. Hruszkewycz , M. V. Holt , C. Huang , I. Calvo-Almazán , U. Jahn , U. Pietsch , L. J. Lauhon , L. Geelhaar
Title: Correlated nanoscale analysis of the emission from wurtzite versus zincblende (In,Ga)As/GaAs nanowire core-shell quantum wells
Source: Nano Lett. , 19 , 4448 ( 2019 )
DOI: 10.1021/acs.nanolett.9b01241

Author: F. Feix , T. Flissikowski , K. K. Sabelfeld , V. M. Kaganer , M. Wölz , L. Geelhaar , H. T. Grahn , O. Brandt
Title: Ga-Polar (In,Ga)N/GaN Quantum Wells Versus N-Polar (In,Ga)N Quantum Disks in GaN Nanowires: A Comparative Analysis of Carrier Recombination, Diffusion, and Radiative Efficiency
Source: Phys. Rev. Appl. , 8 , 014032 ( 2017 )
DOI: 10.1103/PhysRevApplied.8.014032

Author: J. Kamimura , P. Bogdanoff , M. Ramsteiner , P. Corfdir , F. Feix , L. Geelhaar , H. Riechert
Title: p-type doping of GaN nanowires characterized by photoelectrochemical measurements
Source: Nano Lett. , 17 , 1529 ( 2017 )
DOI: 10.1021/acs.nanolett.6b04560

Author: J. Lähnemann , P. Corfdir , F. Feix , J. Kamimura , T. Flissikowski , H. T. Grahn , L. Geelhaar , O. Brandt
Title: Radial Stark effect in (In,Ga)N nanowires
Source: Nano Lett. , 16 , 917 ( 2016 )
DOI: 10.1021/acs.nanolett.5b03748