IVC17 / ICSS13 and ICN+T 2007

Optical studies on chemical and core-shell surface-passivation techniques of InP and GaAs nanowires
Muench, Steffen¹; Reitzenstein, Stephan¹; Hofmann, Carolin¹; Skold, Niklas²; Tragardh, Johanna²; Crankshaw, Shanna³; Chang-Hasnain, Connie³; Samuelson, Lars²; Forchel, Alfred¹ ¹Germany; ²Sweden; ³United States

We report on the optical characterization of chemical and core-shell passivation techniques applied to III-V nanowires. In particular, standard and time resolved micro photoluminescence spectroscopy was employed to investigate the effect of surface passivation on GaAs and InP nanowires. Surface passivation is an important issue in the design and fabrication of high performance nanowire devices due to the large surface-to-volume ratio. In case of GaAs nanowires the surface passivation is of particular interest due to the large surface recombination velocity inherent to this material system. We compared chemical and core-shell passivation techniques applied to GaAs nanowires grown on a (111)B GaAs substrate using Au as catalysts. The core-shell nanowires were realized by overgrowing a GaAs core in a MOVPE reactor with a 50 nm thick Al0.5In0.5P shell. Surface treatment results in an enhancement of free excitonic emission by a factor of about 40 and 110 for sulfur passivated and core-shell NWs, respectively, in comparison to as-grown GaAs NWs. The effect of surface passivation is reflected in a strong reduction of the surface recombination velocity S to 2.5 x 104cm/s for the core-shell NWs (at low temperature) compared to typical values of about 1 x 106cm/s reported for untreated GaAs NWs. In addition, chemical surface passivation of InP NWs by means of hydrofluoric acid was investigated. This etchant not only removes a thin oxide layer surrounding the InP NWs, but also passivates the surface by a thin hydrogen surface-layer inhibiting the formation of surface states. The significantly lower number of nonradiative surface states in the InP material system is reflected in a very low surface recombination velocity of S = 300 cm/s even for the as-grown NWs. Applying HF passivation further reduces nonradiative surface states and leads to a (almost) negligible non-radiative surface recombination associated with a monoexponential decay of the free carrier concentration.

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