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Accueil du site > Vie du laboratoire > Congrès / Colloques / Conférences > Optical Properties of Individual Nanowires and Quantum Dots in High Magnetic Field, Septembre 2014 > Programme du workshop > Abstract : Magneto-photoluminescence studies of wurtzite III-V nanowires

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Abstract : Magneto-photoluminescence studies of wurtzite III-V nanowires

Magneto-photoluminescence studies of wurtzite III-V nanowires

A.Polimeni

Dipartimento di Fisica, Sapienza Università di Roma, Roma, Italy

 

The possibility of growing semiconductor nanowires (NWs) in the zincblende (ZB) and/or wurtzite (WZ) crystal phase widens the potential applications of these nanostructures. This is particularly true in technologically relevant III-V compounds, such as GaAs, InAs, and InP, for which WZ is not available in bulk form. Although the WZ band structure of many III-V NWs has been widely studied, the transport (i. e., carrier effective mass) and spin (i. e., carrier g-factor) properties are almost experimentally unknown. These are key parameters that need to be understood, if the WZ NWs and their crystal-phase homostructures are to be utilised in novel optical and electronic applications.

In our work, photoluminescence (PL) spectroscopy was used to study the effects of very intense magnetic fields (Bup to 28 T) on the electronic properties of WZ NWs. The focus of this talk will be on InP, mainly. Indeed, InP NWs can be used as a good model system for this study, since the interplay between structural and electronic properties of WZ InP has already been widely investigated.

First, power- and temperature-dependent PL, as well as time-resolved PL measurements were used to disentangle impurity-related transitions and free-exciton recombination. Then, magneto-PL was performed at 4.2 K and 77 K to emphasize the spectral contributions due to impurities and free-excitons, respectively. Finally, the magnetic field was applied parallel and orthogonal to the WZ ĉ-axis in order to highlight possible anisotropies in the diamagnetic shifts and Zeeman splittings that are inherent to the NW crystal symmetry.

We find a sizable increase in the exciton effective mass in WZ InP NWs as compared to ZB InP bulk and a dependence of this fundamental parameter on the motion direction with respect to the NW main axis. Magneto-PL at low temperature reveals Landau levels associated to bands involving free-carrier to impurity recombination that should help separating the contribution of electrons and holes to the exciton reduced mass. Finally, markedly different values of Zeeman splitting (namely, carrier g-factor) and field-induced circular dichroism of emitted light are observed for different Bdirections. A comparison with results obtained in other III-V WZ NWs will be presented.

All these findings are related to the main features of the conduction and valence band of WZ NWsand may guide the design of devices based on the unique properties of these nanostructures.