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IrOx–carbon nanotube hybrids: A nanostructured material for electrodes with increased charge capacity in neural systems

IrOx–carbon nanotube hybrids: A nanostructured material for electrodes with increased charge capacity in neural systems

Acta Biomaterialia, Volume 10, Issue 10, October 2014, Pages 4548–4558.     Nina M. Carretero, Mathieu P. Lichtenstein, Estela Pérez, Laura Cabana, Cristina Suñol, Nieves Casañ-Pastor

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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