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Surfactant-free CO2-based microemulsion-like systems

Surfactant-free CO2-based microemulsion-like systems

                                                         Robert F. Hankel, Paula E. Rojas, Mary Cano-Sarabia, Santi Sala, Jaume Veciana, Andreas Braeuer* and Nora Ventosa* Chem. Commun., 2014,50, 8215-8218

Intraband Absorption in Self-Assembled Ge-Doped GaN/AlN Nanowire Heterostructures

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nl-2014-002247 0008

M. BeelerP. HilleJ. SchörmannJ. TeubertM. de la MataJ. ArbiolM. Eickhoff, and E. Monroy*

Nano Lett., Article ASAP

DOI: 10.1021/nl5002247

We report the observation of transverse-magnetic-polarized infrared absorption assigned to the s–pz intraband transition in Ge-doped GaN/AlN nanodisks (NDs) in self-assembled GaN nanowires (NWs). The s–pz absorption line experiences a blue shift with increasing ND Ge concentration and a red shift with increasing ND thickness. The experimental results in terms of interband and intraband spectroscopy are compared to theoretical calculations of the band diagram and electronic structure of GaN/AlN heterostructured NWs, accounting for their three-dimensional strain distribution and the presence of surface states. From the theoretical analysis, we conclude that the formation of an AlN shell during the heterostructure growth applies a uniaxial compressive strain which blue shifts the interband optical transitions but has little influence on the intraband transitions. The presence of surface states with density levels expected for m-GaN plane charge-deplete the base of the NWs but is insufficient to screen the polarization-induced internal electric field in the heterostructures. Simulations show that the free-carrier screening of the polarization-induced internal electric field in the NDs is critical to predicting the photoluminescence behavior. The intraband transitions, on the other hand, are blue-shifted due to many-body effects, namely, the exchange interaction and depolarization shift, which exceed the red shift induced by carrier screening.

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