We have investigated single GaAs NWs by micro-photoluminescence and spatially resolved cathodoluminescence spectroscopy. The luminescence spectrum of GaAs NWs consisting of WZ and ZB segments is spread over a wide spectral range (cf. Fig. 1), where the optical emission occurs either predominantly above or below the energy gap of ZB GaAs (EgZB) depending on the growth conditions. These results are explained by means of a qualitative model assuming that EgWZ is larger than EgZB and that GaAs NWs with alternating ZB and WZ segments along the wire axis establish a type-II band alignment, where electrons captured within the ZB segments recombine with holes of the neighboring WZ segments. Thus, the corresponding transition energy depends on the degree of confinement of the electrons, i.e., on the thickness of the ZB segments and exceeds EgZB only for very thin ZB insertions. At low temperatures, the incorporation of carbon acceptors plays a major role in determining the spectral profile, as these can effectively bind holes in the ZB segments. Our results clarify why in some previous investigations a luminescence signal was only observed for energies below EgZB, while in other studies a luminescence signal was also observed above the energy gap of ZB GaAs. From the cathodoluminescence measurements of single GaAs NWs performed at 300 K, we deduce a lower bound of 55 meV for the difference between the corresponding energy gaps, i.e.EgWZ-EgZB (cf. Fig. 2).
|1||Author||U. Jahn , J. Lähnemann , C. Pfüller , O. Brandt , S. Breuer , B. Jenichen , M. Ramsteiner , L. Geelhaar , H. Riechert|
Luminescence of GaAs nanowires consisting of wurtzite and zinc-blende segments
|Source||Phys. Rev. B , 85 , 045323 ( 2012 )|
: 10.1103/PhysRevB.85.045323 |
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